So I got this Sony PC monitor from 1992 that didn't work when I picked it up. I went ahead and tested all the caps and replaced anything bad. There was a absolute ton of caps that had gone high ESR (we are talking 300kOhms high) and there is one board in particular, the DA board, that used surface mount caps which had leaked all over the place.

On the DA board, I removed all the caps and clean it thoroughly with white vinegar and let it sit until it stopped foaming. I cleaned that off and then soaked it with 99% IPA and dried it off with compressed air and let it sit for days to make sure it was dry. The DA board is almost all surface mount, and there are no transformers or anything that might get messed up by being wet. I sprayed all the pots with deoxit and fiddled them a bit to make sure they didn't harbor salts or crust from the whole process.

I also inspected the DA board under a microscope and tested continuity on any areas that seemed more corroded. There didn't appear to be any such issues, and the traces didn't seem to be broken, only exposed in some areas. I suppose it's possible that something under an IC is bad, or a via got damaged because it's a multi-layered board with components on the back side. There is absolutely no apparent damage to the back side.

When I got everything back together, I turned on and I got HV, but the image was vertically collapsed. It's only a few pixels high, but it's there enough that I can actually make out the colors in the line and it reflects what should be seen on the screen. For example, I can see where the Windows logo starts and stops on boot, and I can see the proper colors change on the raster horizontally (for example a SMPTE bar image will reflect the bars color across the screen). I can also successfully shift the image horizontally with the screen controls.

My first thought was that the bad caps on the D board might have blown the Vertical Output IC before I got it, as I have run into that issue a number of times. I bought a handful of the ICs pretty cheaply, but replacing it didn't help or apparently change anything. I thought maybe the replacement could be bad, but a thorough check of the original IC revealed no shorts on the IC, and diode tests between pins seem to make sense for a working IC. I don't believe the original IC was bad at all. I suppose it's still not impossible, but I think it's okay. Anytime this has happened to me in the past, the IC had shorts or low resistance between GND and Vcc or some other pin(s).

So I'm kind of lost here just checking random things. It's extremely difficult to test voltages on this monitor because the portion of the case that holds the CRT is extremely thin and can't be supported by it's structure alone. The only way I could get it to stand up and make adjustments on the inside was to prop it up leaning forward on a towel and balance it that way. Doing this it's not possible to access the bottom of the PCB to take readings. So I disassembled the chassis again and I'm just looking more closely at the DA board in hopes that I can find a culprit.

There are a number of small ICs on the DA board that handle all the V and H stuff, and choosing the resolution, I assume based on the frequency of the incoming signal.

Can someone help me to identify which components or areas can cause this condition?

Again this is:

-General Vertical Collapse

-There are still a couple of pixels present, enough to match what you are displaying to those few lines as the input changes

-Horizontal seems to be okay in that it spans the whole screen and it is movable with controls

-High Voltage appears to be present as I'm getting the whine and the static on the screen

-Area around the Vertical output IC on the PCB is dark from heat, but none of the component are visually burned or bad and testing a couple so far they looked perfect.

Here is a link to the three pages of the schematic on imgur. I didn't want to put them in-line as they are 11x17 size and would be too big here. If you open the image links and then view them in another tab, you can expand them to see details.

D board:
https://i.imgur.com/WPsfh6y.png

DA board:
https://i.imgur.com/cd66Twn.png

Neck board:
https://i.imgur.com/sW2mfuv.png

TIA

I did some more work on this project and was able to get things balanced in such a way that I could take some readings with my scope.

What I found was that I am getting what appear to be correct waveforms on the DA board when I have a standard 31kHz VGA signal plugged into the monitor.

I tested several TPs, but specifically I was able to confirm that I'm getting both proper Vertical deflection signals in from the VGA cable, and that the Vertical Deflection signal looks exactly as the SM says it should when it leaves the DA board.

I'm not sure if this means I can rule out the DA board completely, but I am more suspecting that the Vertical Deflection just isn't spinning up at all.

I already replaced the Vert output IC, and replaced the caps around it (and every other bad cap on the board), so I don't know what to try next.

Also have checked the windings on the yoke and they seem to read what I would expect in both cases.

Any ideas?

So I isolated the 24VDC rail to the Vertical output IC as the culprit and traced the issue back to a fusible resistor at the transformer. It most likely blew as a result of bad caps in the power supply that I have replaced, so it's getting Vertical deflection now.

Unfortunately, I'm still having some issues with the Geometry. I can't seem to get the Pin Amp controls to straighten the sides out.

After much tweaking around with the various controls, I think it's got to be some component in the Pin Amp section of the DA board that is wrong.

Any ideas on what to focus on?

This is the section of the schematic that contains the Pin Amp stuff, and you can see the whole thing in my first post via the imgur links.

https://i.imgur.com/ElXADDR.png

I think you probably missed a cap in there. Caps are high fail in these. Then there's the vertical output IC also.

I think you probably missed a cap in there. Caps are high fail in these. Then there's the vertical output IC also.

Nope. Didn't miss any caps. Especially not on the DA board. It's a tiny board that was mostly surface mount caps. Took em all off and all the through hole caps as well.

As I said in my last post, the Vertical is working now, unless you think the Vertical output IC could have an effect on the Pin Amp circuit on the DA board?

I did replace the Vertical IC with an NOS part, so there could be something wrong with the new one, but I don't think it's specifically handling the East West stuff, that's on the DA board.

It's using a TEA2031A for the geometry adjustments, and when I spray the thing with cold spray it gets wiggly and it looks like it's pulling the sides in. So I'm suspecting that one. I can get it cheap so I just got one coming regardless.

Attached is the datasheet

Indeed it can be the IC, but you changed also the low value electros in this area?

Indeed it can be the IC, but you changed also the low value electros in this area?

Yes, I had to change all the low value eletros. All the surface mounts spilled their guts, and the few through hole caps were quite bad. I checked the orientation of the caps many times, I didn't make any mistakes.


I tested the Pin Amp IC:

Pin 5) correct. 20 Vpkpk square wave @ 31.15kHz

Pin 6) correct 20VDC on it

Pin 7)14VDC offset from schematic is present, but the 0.5Vp-p waveform is screwy and wrong. It looks more like a sawtooth than what the schematic shows, and it's only about 250mV, not 500

Pin 8) 3.4 V pkpk sawtooth. Very close to the 3.6V pkpk shown in the service manual.

So from this I can conclude that something is fishy around the chip or inside the chip. Pin 7 is connected to ground through a 150k resistor, but in this set, it's also connected to the rest of the circuit through a 470k resistor with a cap to ground between them. I have no idea why it's done, but I can guess that maybe it's some kind of DC restoration to bring the level of the chip up to the rest of the circuit on pin 7 or possibly to enable some of the other geometry controls in some way.

Pin 7 is connected to Pin 5 through the one resistor, and the waveform on Pin 5 looks correct, so therefore, I'd basically assume that there's either something wrong with the chip, or with one of the components going to ground between the Pins.

R376- 150k - to GND from Pin 7

C340- 0.0015 - to GND from Pin 7

R375- 470k - between Pin 7 and Pin 5

Does this result say anything to you about the circuit or the failure I'm seeing; it's like something in the circuit is bring down the 500mVpkpk parabola I'm supposed to see to ~280mV and squishing the top down into noise

I attached the expected waveforms from Pins 5,7 and 8 of the Pin Amp IC, Pin 6 is the supply is supposed to be 20 V and it is.

Yes, I had to change all the low value eletros. All the surface mounts spilled their guts, and the few through hole caps were quite bad. I checked the orientation of the caps many times, I didn't make any mistakes.


I tested the Pin Amp IC:

Pin 5) correct. 20 Vpkpk square wave @ 31.15kHz

Pin 6) correct 20VDC on it

Pin 7)14VDC offset from schematic is present, but the 0.5Vp-p waveform is screwy and wrong. It looks more like a sawtooth than what the schematic shows, and it's only about 250mV, not 500

Pin 8) 3.4 V pkpk sawtooth. Very close to the 3.6V pkpk shown in the service manual.

So from this I can conclude that something is fishy around the chip or inside the chip. Pin 7 is connected to ground through a 150k resistor, but in this set, it's also connected to the rest of the circuit through a 470k resistor with a cap to ground between them. I have no idea why it's done, but I can guess that maybe it's some kind of DC restoration to bring the level of the chip up to the rest of the circuit on pin 7 or possibly to enable some of the other geometry controls in some way.

Pin 7 is connected to Pin 5 through the one resistor, and the waveform on Pin 5 looks correct, so therefore, I'd basically assume that there's either something wrong with the chip, or with one of the components going to ground between the Pins.

R376- 150k - to GND from Pin 7

C340- 0.0015 - to GND from Pin 7

R375- 470k - between Pin 7 and Pin 5

Does this result say anything to you about the circuit or the failure I'm seeing; it's like something in the circuit is bring down the 500mVpkpk parabola I'm supposed to see to ~280mV and squishing the top down into noise

I attached the expected waveforms from Pins 5,7 and 8 of the Pin Amp IC, Pin 6 is the supply is supposed to be 20 V and it is.

Makes all sense. We can imagine the waveforms differing a little according with CRT variances, but certainly not a radical difference. At least with my experiences with modern TV when I repairing it (and monitors), is that the waveforms always resemble the originals when it are working well. Besides the suspicious DC voltages.

Makes all sense. We can imagine the waveforms differing a little according with CRT variances, but certainly not a radical difference. At least with my experiences with modern TV when I repairing it (and monitors), is that the waveforms always resemble the originals when it are working well. Besides the suspicious DC voltages.

Thanks. I went ahead and probed Pins 1 and 2 of the Pin Amp IC, and it seems like the AC component that's supposed to vary the parabola on the IC's output is not properly varying when I adjust the Pin Amp potentiometers.

I am now thinking it's most likely the fault of the IC, but also maybe it's some other component in the circuit holding the IC down at the input or output.

Does anything jump out to check?

Be sure the V out is getting + 24 VDC. I hate shot gunning BUT if
it has @24 V change the IC & all related 'lytic caps, ALL at once.
While things are removed do resistant tests. That will fix 95% of them.

Zeno:smoke:
LFOD !

Be sure the V out is getting + 24 VDC. I hate shot gunning BUT if
it has @24 V change the IC & all related 'lytic caps, ALL at once.
While things are removed do resistant tests. That will fix 95% of them.

Zeno:smoke:
LFOD !

Yes, it's getting 24V out of the transformer now. I also scoped Pin 6 on IC303 (East West IC) and it has the indicated 20.5V supply. In fact, all of the Pins around IC303 look hunky dory except Pin 7, which is suppose to be the parabola.

I changed all the caps on the DA board already because they were the early surface mount kind and were all dead. So unfortunately I can't do resistance tests with them out of circuit.

I've got a new East West IC coming on monday, so I'll try my luck with that and cross my fingers. Otherwise, I might have to remove the caps and start looking for an open resistor or something.

I replaced IC303 and I still have the weird Side Pin issue. I've been checking resistors all over the board, pulling stuff out when I have to, but I'm still not seeing any issues.

If anyone has an idea of what would maybe cause this to narrow my search I would be grateful.

So this is the output of Pin 5 on IC303. I realize now that the top of it is the key to understanding the pincushion adjustment output. If you look at the top of the waveform, it's supposed to have a flat top that extends past the edges of the square wave evenly on both sides.

This waveform is incorrect as it has the top portion skewed all the way to the left. The waveform wiggles around in a manner that perfectly reflects when I tweak the Pincushion pots, and it snaps back to the left as the sides of the raster similarly refuse to be corrected.

https://i.imgur.com/cGyMb8O.jpg

Now I can see why it's displaying incorrectly, but I don't know why or where the problem lies. I've already spent a long time checking voltages, and nothing really seems wrong so far. I've more or less confirmed the values of all resistors, and I checked the ICs that control the mode selection.

Where should I focus my attention?

To add to the last post. This waveform is shown in the Service Manual here, and it shows that it's supposed to have a symmetrical top portion. Also of note is that the DC voltage on the output of Pin 5 is called out as 4.6V in the SM, but it measures 8VDC with a DMM.

The output of Pin 7 is also incorrect; it's a smooshed sawtooth looking thing and nothing like what it is supposed to be. I have to assume something is wrong either on the input side (Pins 1&2) or the output side (between Pins 7 and 5, or further downstream from 5).

I see the basically correct symmetrical 6.4VDC on pins 1&2 (SM says 6.5, but that's pretty close I think), but the parabola is driven by current and not voltage, so I'm not sure if just having those two correct voltages is enough, and I'm not sure how to tell if there is imbalance in the current draw (or what to do with that information if I had it).

I've followed the output as far as the last set of transistors in the Pincushion circuit (which control the Pin Balance), and the voltages at those transistors appears to be correct.

https://i.imgur.com/O6M2OaQ.pnghttps://i.imgur.com/7bxIy2I.png

I am still bewildered by the Pincushion issue, but I found an area of the circuit that seems to be a little amiss.

There's some readings that are what I would call "shaky," or that they bounce up and down a bit on the scope and are hard to lock in with the trigger.

Also there are some areas that the voltages are a little bit off; nothing is extremely off, but there are some spots that look about 1V or so off.

The "worst" of these spots is around Q312, which is supposed to be 9V on the collector, but it's a little above 10V and bounces around up and down. The base is supposed to be 3.9V, but it's 3.3, and the emitter is supposed to be 3.2V and it's 2.7V.

Normally, this wouldn't look like a smoking gun to me (and it doesn't really), but I'm not seeing anything else much wrong still, and it's right in the "Side Pin" circuit, which is a prime area that looks to be malfunctioning.

I'm sure I am measuring the circuit with the correct conditions (31kHz, color bars), and everything else on the DA board is almost dead-nuts under these conditions, so I believe I have it right.

So I ordered up some 2SC1632's and I'll start off by replacing Q312 and see if that helps. If it does nothing, I can try Q311, 314, and 315 as the are all in the same circuit and all have a tiny bit of voltage variation from the SM, but none of them are more than Q312 is.

This is my readings. Green is dead-nuts, Yellow is slightly off in some way. The yellow circled resistor values are all in circuit, so I expect them to be off. Of course, if any of those looks weird, then please let me know. Sorry it's so messy, but that's how I've been keeping track of things.


https://i.imgur.com/9K2n3LJ.png

If it bounces in a undetermined random time, some R, C or some transistor (like the ones you will replace) must be with some issue. Some internal corrosion etc.

If it bounces in a undetermined random time, some R, C or some transistor (like the ones you will replace) must be with some issue. Some internal corrosion etc.

I figured as much. I can't imagine the ceramic chip caps or the resistors are at fault because they are such simple devices, and at least the resistors are basically reading the correct values (I haven't tried to remove and test all the little caps).

The transistors and maybe diode seem to be more suspect because they are more complicated devices that could be partially effected by some small amount of internal corrosion. I tested the diodes in the area for leakage and they seem good too, so I feel like I'm left with one or more marginal transistors creating sneaky havoc

Yes, the best bet is the semiconductors. Yet, if all are good, don't give up:
https://www.worldphaco.com/uploads/RESTORING_THE_SONY_MICRO.pdf
In this example, the restorer found a 100R noisy R in the AFC circuit.

Yes, the best bet is the semiconductors. Yet, if all are good, don't give up:
https://www.worldphaco.com/uploads/RESTORING_THE_SONY_MICRO.pdf
In this example, the restorer found a 100R noisy R in the AFC circuit.

True it's always possible. Probably a lot less so with 90s resistors than with the resistors in that early 60s Sony set.

I won't give up, at least not anytime soon. I fixed a shortwave radio once that took me years. I had to put it aside for awhile and the when I came back to it fresh it kind of clicked and I figured it out.

Although, this is looking pretty much like I'll have to brute force things to some extent.

All I have currently is some slightly wrong voltages, so I'll start there.

True it's always possible. Probably a lot less so with 90s resistors than with the resistors in that early 60s Sony set.

I won't give up, at least not anytime soon. I fixed a shortwave radio once that took me years. I had to put it aside for awhile and the when I came back to it fresh it kind of clicked and I figured it out.

Although, this is looking pretty much like I'll have to brute force things to some extent.

All I have currently is some slightly wrong voltages, so I'll start there.

This long time occurred to me more than one time. Last time, was with a delta-gun TV, with a jittery unstable vertical only half a minute in a 2 hours interval (absolutely random); and after the hiccup, the vertical changed linearity a little (sometimes a lot). When I stomped in a convergence pot, finally I discovered the trouble... of course, vertical output is CCS, so a variation of the convergence resulting impedance will distort the vertical due to load variation. Took me 2 years to discover it... I cleaned the offending pot, and the problem never returned.
Also time to dedicate to it are short, so I used it as-is when symptoms are more light, until it become worst.

I replaced the IC303 with another part, and the other transistors in the 300 range, which are largely related to the Pincushion circuit. After getting it back together, I checked voltages and found that some of them are correct now that were slightly off before, but I have one new issue that I didn't have before.

I found that I have lost width control, and there is some kind of short or something going on that I have not been able to track down the cause of at all.

The Pincushion IC is connected to the Vert position circuit through Q255, the collector of which is connected to Pin 2 on IC303. It is supposed to be 2.2V at the Collector of Q255, and then end up at 6.5V at Pin 2 of IC303.

Basically what's happening now is that the voltage at Pin 2 of IC303 changes with the Vertical Position pot, which is obviously wrong. I've checked all the transistors and diodes in the area and can't find an issue. I also checked IC205 for shorts between pins and found nothing.

There is 22V at the Emitter of Q254, which will change the voltage present at the bottom of D257, and then raise the voltage at the base of Q255, which finally raises the voltage at the collector of Q255 and that voltage shows up on Pin 2 of IC303.

It's also possible that something in the switching section of the circuit is functioning incorrectly as perhaps if the various diode arrays were getting the wrong input somewhere, it might lead to a weird mixed outcome for the cumulative output. The connection between the Vertical position circuit also is impacted by the switch which goes between the presets and the external V/H size and position controls. The switch is not a simple on/off, but a ground/not ground signal sent to the anode of D609, which turns Q615 on or off.

FYI, the service manual wants me to take all voltages and waveforms with a 640x400 70Hz color bars pattern, which is what I have been doing.


I replaced Q254 and Q255 with brand new exact replacement transistors (all of the SMD transistors and diodes are still available cheap for this PCB thankfully), and I tested D257 and it looks like a working diode. It's a Diode package that has one anode and two cathodes.

The junction betwen D257 and Q254 is 22V when it should be 7.7V and I really can't figure out what's causing it at all.

Any ideas?

https://i.imgur.com/YOEec95.png

I replaced the IC303 with another part, and the other transistors in the 300 range, which are largely related to the Pincushion circuit. After getting it back together, I checked voltages and found that some of them are correct now that were slightly off before, but I have one new issue that I didn't have before.

I found that I have lost width control, and there is some kind of short or something going on that I have not been able to track down the cause of at all.

The Pincushion IC is connected to the Vert position circuit through Q255, the collector of which is connected to Pin 2 on IC303. It is supposed to be 2.2V at the Collector of Q255, and then end up at 6.5V at Pin 2 of IC303.

Basically what's happening now is that the voltage at Pin 2 of IC303 changes with the Vertical Position pot, which is obviously wrong. I've checked all the transistors and diodes in the area and can't find an issue. I also checked IC205 for shorts between pins and found nothing.

There is 22V at the Emitter of Q254, which will change the voltage present at the bottom of D257, and then raise the voltage at the base of Q255, which finally raises the voltage at the collector of Q255 and that voltage shows up on Pin 2 of IC303.

It's also possible that something in the switching section of the circuit is functioning incorrectly as perhaps if the various diode arrays were getting the wrong input somewhere, it might lead to a weird mixed outcome for the cumulative output. The connection between the Vertical position circuit also is impacted by the switch which goes between the presets and the external V/H size and position controls. The switch is not a simple on/off, but a ground/not ground signal sent to the anode of D609, which turns Q615 on or off.

FYI, the service manual wants me to take all voltages and waveforms with a 640x400 70Hz color bars pattern, which is what I have been doing.


I replaced Q254 and Q255 with brand new exact replacement transistors (all of the SMD transistors and diodes are still available cheap for this PCB thankfully), and I tested D257 and it looks like a working diode. It's a Diode package that has one anode and two cathodes.

The junction betwen D257 and Q254 is 22V when it should be 7.7V and I really can't figure out what's causing it at all.

Any ideas?

https://i.imgur.com/YOEec95.png

Hmmm... multiscan monitor... a lot of things to see...

22V? The IC are responding ok to the logic on it's inputs (the IC250)? Or, if something ahead the P302 are throwing this voltage (eg. with RV257 closed)?

Likely, some cascade of events can occur.

Hmmm... multiscan monitor... a lot of things to see...

22V? The IC are responding ok to the logic on it's inputs (the IC250)? Or, if something ahead the P302 are throwing this voltage (eg. with RV257 closed)?

Likely, some cascade of events can occur.


I'm not sure how to check if there's an issue with IC250. I checked for shorts, and there's no shorts between any of the pins; all pins are no connection to each other.

From the datasheet, there doesn't seem to be a way that 20+ volts is produced by Pin 10 unless there is some internal short?

This is why I though the 20+ volts is coming from somewhere else further down.

Transistor arrays are new to me. This one looks this way on the inside:

https://i.imgur.com/N5uVcGq.png

An array is a simple form of IC not having power supply sometimes, so rarely have any processing. Basically the cause can be external to it (sometime trowing 20V there).
Anyway, the pin 9 must have higher voltage than the others, or the internal diode conducts.
The problem must be with any of the outputs if it don't reacts with the input.

An array is a simple form of IC not having power supply sometimes, so rarely have any processing. Basically the cause can be external to it (sometime trowing 20V there).
Anyway, the pin 9 must have higher voltage than the others, or the internal diode conducts.
The problem must be with any of the outputs if it don't reacts with the input.

And so I measured the logic circuit approaching IC250 and I found a problem with inputs on IC604, which directly feeds the network of transistors leading to the inputs of IC250.

Pin 1 of IC604 is LOW when it should be HIGH. This is causing Pin 5 to be LOW when it should be HIGH.

I traced the input for Pin 1 IC604 back, and it's connected to the collector of Q613, and also to the 12V line through some resistors.

The Base of Q613 is connected to the output of D609.

D609 is switched on and off by the Auto/Manual switch for the horizontal and vertical size and position. The switch goes between GND and Open Circuit.

D609 measures correct on it's other side (toward Q615), but it reads 2.7V on the side towards Q613 when it should read 0V.

I can see that the input of Pin 1 on IC604 being wrong will cause certain problems, but I can't tell if this problem is because D609 give incorrect voltage, or because the 6.5V which should be present on the other side of Q613 is not there for some other reason.

I also cannot see why this possible "cascade" problem would create 24V on Pin 10 of IC250. If I had to make a guess, I would tend to believe there is an issue creating the 24V on Pin 10 of IC250 and that is leading to, or also causing the loss of 6.5V on other side of IC250.

I measured all other logic ICs in this circuit (IC601, 602, 603, 605, 606) and I found that all voltages were correct on all pins of all ICs.

I replaced Q613 with a new part of the exact same transistor (they are still available) and that didn't fix it. The old transistor measured to be a bit weak and measured different from new part, so I thought it was worth a try.

I have replacement ICs for logic coming in the mail, luckily they are all also available and very cheap.

This is what I am seeing, with incorrect voltages in red:


https://i.imgur.com/IecusN1.png
https://i.imgur.com/DQFelQo.png

So, the AUTO switch, connected to GND, can extinguish Q615 and Q613, unless have some fail in this line.
The IC 604, it follow the truth table in the datasheet? Too busy at moment to analyze it but, a question: perhaps 0V in the pin 1 causes 0V in the outputs?

The IC 604, it follow the truth table in the datasheet? Too busy at moment to analyze it but, a question: perhaps 0V in the pin 1 causes 0V in the outputs?

Yes, IC304 definitely follows the truth table of its datasheet. The incorrect voltage on Pin 1 causes 0V on Pin 5 output.

https://i.imgur.com/pxbhIdS.png

Pin 1 should be HIGH, and the 4 outputs it controls should all be HIGH, instead it becomes HLHH

So the 2.7V on base of Q613 maybe is the problem. Or possibly the lack of 6.5V on the collector of Q613 causes the 2.7V to appear on the base.

I don't know the chicken or the egg unfortunately


Edit: I'd like to add that I isolated IC250, Pin 10 to try and see where the 23V is coming from that shouldn't be there, and without Pin 10 connected to the rest of the circuit, it no longer has the 23V on it, but I still see 23V all over Q254 and the Vertical Position potentiometer. Not sure why it's wrong, but I also can't see how it's connected to the issue with IC604.

Also makes wonder if D608 are not resistive or open, or some trouble with this line (the circuit/switch for the AUTO/Manual are inoperative?). Certainly one function corresponds (the one making GND connection) to basically near 0V on the cathode of D608. Then the cathode of D609 will presents very low voltage I suppose. Unless...
The cathode of D609 is connected to another thing in the circuit, or is only to Q613?

Also makes wonder if D608 are not resistive or open, or some trouble with this line (the circuit/switch for the AUTO/Manual are inoperative?). Certainly one function corresponds (the one making GND connection) to basically near 0V on the cathode of D608. Then the cathode of D609 will presents very low voltage I suppose. Unless...
The cathode of D609 is connected to another thing in the circuit, or is only to Q613?


I can say at least that switching Auto/Manual control does indeed still switch the control mode. The horizontal size doesn't work at all, but the position controls all work somewhat. The vertical position "works," but it shows up in the wrong spot (too far down).

The cathode of D609 (right side) goes only to the base of Q613, nowhere else. It's at 2.7V. The collector of Q613 is supposed to be 6.5V, but it's 0V, the emitter of Q613 is grounded.

The other cathode touches Q615 and IC602/604, but that voltage is correct.

The anode goes to the switch between GND/Open and the two resistors that connect it to the 5.5V rail.

The main problem I'm seeing is the lack of 6.5V on Pin 1 of IC604. That bad logic sees the circuit between it and the other two diode arrays, IC250 and IC302 incorrect. But I don't know if the problem comes from D609 side or IC250/IC302 side. Can bad voltage(s) on output side of those ICs cause cascade failure back towards D609?

You can see that lack of 6.5V on the circuit to the right of IC604 has a lot of problems for the logic. It flips the logic level on 5 Darlington pairs inside IC250 and 4 pairs inside IC302.

https://i.imgur.com/APQxtke.jpg

A little more troubleshooting has ended with my now losing the raster mostly. If I turn up the G2 a bit I can see something, but it's all messed up.

If I display something with color it doesn't seem to come up, it's just a murky white raster, but it will sync to a black and white image a little bit if i tweak the free running horizontal frequency to match it

I pulled IC250 and IC320 and they test normally and identical to a new part, so I think they are okay. Pretty much every part I test is okay, and yet things are still wacky over by those two ICs.

I did notice that the voltage on Q317 is also very off, I'm assuming because of Pin 10 of IC302, and that it's connected to a relay on the D boards. Although I don't see how that would effect things, I can tell there's some switching problem with the Multiscan circuit because it's not kicking thing into gear correctly.

The only other lead I can think of is that I had to replace Q310 twice already before things went totally south. It's now acting just fine I believe, so perhaps whatever is wrong now is somehow related to Q310 blowing previously.

Q310 was involved with this area where I thought there was an 18V zener diode missing (but it turned out after looking at photos that it was unpopulated). Once I replaced Q310 the voltages in this area all started looking good, but then it developed this new (seemingly worse) issue.


https://i.imgur.com/SJEU1xF.png

So the multiscan not operates correctly? We presume then the wrong auto setted voltages as a result.
What is the scan rate detector, a µcontroller or a bunch of logic IC's?

So the multiscan not operates correctly? We presume then the wrong auto setted voltages as a result.
What is the scan rate detector, a µcontroller or a bunch of logic IC's?

A bunch of logic ICs and discrete components.

The Horizontal and Vertical Sync signals come in directly from the VGA cable to the Multisync PCB, while the color information is sent directly to the Neck PCB.


EDIT:

Ok, I managed to get the raster back to what I had last week where I can see the image, but I do not have (much) Vertical Position control. I have Vertical Size, Horizontal Size, and Horizontal Position, but Vertical Position is just a tiny little bit, and it's always basically too low down on the raster. I have no Pincushion controls (even less than when I first started).

I removed IC604, IC250 and IC302 and replaced them with new parts and just kind of did my best to reflow anything I had reworked and that made the raster come back.


I still have the problem with Zero Volts in the area beyond Pin 5 of IC604.

I switched the resolution to 1024x768 to see how that would change things, and I am seeing 18V on the base of Q317, which I don't think should be there. This connects to a Relay on the D PCB, so I thought maybe it's a problem on the D board, but I measured the Pin on the connector that goes out to the RELAY and it's around 4.3V while the Base of Q317 is 20V. It interacts with Q616, so I measured the Base of that and it's at it's correct 5.5V, so I don't think this is a problem over there.

I guess it must be all coming from the other side of the circuit?

Okay, I maybe tracked down a possible cause, but I'm not sure exactly what might be wrong.

I followed bad voltages around on the board, and I found one that I can trace back to the D PCB through the Vertical Position Signal (which seems to be what's FUBAR).

The Base of Q255 connects to D257 and to the D PCB through Pin 19 of P302. This should be at 8.3V but it's 1.3V. This has got to be wrong I'm thinking.

This 8.3V is supposed to be driven by Q202 and Q203. I actually did think that this might have been contributing sometime a couple weeks ago, so I pulled these two transistors and they tested okay with a simple diode test out of circuit.

I measured the voltages on Q202, and the other two voltages are pretty close to correct, so something here is amiss.

Again, I still don't really understand this stuff totally, so for all I know, the 1.2V is being pulled down from the other side where D257 and Q255 live.

This is what the area looks like:
https://i.imgur.com/pIyNfiv.png

https://i.imgur.com/4s7KRMN.png

With 0V on pin 11 of these IC, indeed we can have low voltage in the V_POSI.
So the command for this IC can be wrong (like wrong scan detect or some fault, or false protection detection maybe). If the IC is good.
But then, Q203 must follow it and then this emmiter voltage needs to be low, or it is inoperative.

With 0V on pin 11 of these IC, indeed we can have low voltage in the V_POSI.
So the command for this IC can be wrong (like wrong scan detect or some fault, or false protection detection maybe). If the IC is good.
But then, Q203 must follow it and then this emmiter voltage needs to be low, or it is inoperative.

Thanks Alex

I measured Q202,203 and I found that the Base-Emitter was very higher, like 1.5V which is way to high, so I assume it's toasted and that would explain the lack of 8.3V.

I am wondering if this situation can be responsible for the lack of 6.5V on Pin 1 of IC604?

There's supposed to be 25V on Pin 11 of IC250. This is missing because the 8.3V is missing on the Base of Q255 and the Anode of D257.

Maybe the 25V on Pin 11 of IC250 closes the transistor input at Pin 6 (of IC250) and bring it to zero. That closes anodes of D255 and then zero volts appears at Collector of Q612. This causes 6.5V to flow through Base of Q612 and to the collector of Q613 and Pin 1 of IC604. Possibly make sense?

In this explanation I am suggesting that the input of IC250 (Pin 6) is being pulled high because of the lack of voltage on its output (Pin 11)

I traced out the voltage path to look at how it's flowing and maybe how it should flow:

https://i.imgur.com/I6hMbrT.jpg

The pins 2 and 3 of IC604 are with proper correct levels? I presume these being from the scan rate detector section.

The pins 2 and 3 of IC604 are with proper correct levels? I presume these being from the scan rate detector section.

Yes they are correct. Pin 2 is at 5.2V (supposed to be 5.5, but seems close enough), and Pin 3 is at 0 volts. All Pins on IC604 are correct except Pin 1 and Pin 5.

I spoke a little with someone who has suggested to me that the 2.7V on the Base of Q613 is probably correct, and it's because the Service Manual must use the "Manual" setting on the Auto/Manual control which grounds out the D609/D608 OR Gate switch.

I had been assuming that the switch was supposed to be set to "Auto" for schematic voltages because Service Manual mentions to use "Auto" setting for setting up voltages and frequency potentiometers on the board in the setup instructions, but it doesn't actually ever say what setting that switch should be at for the schematic voltages.

So doing the math, this person was able to figure out that 2.7V is the correct voltage for that spot when the Cathode of D609 is biased towards the Base of Q613.

So that 2.7V is a red-herring and the whole Auto/Manual switch area is fine. The problem is all on the Collector side of Q613.

I think pretty certainly that Q203 is the cause of the missing 6.5V on Pin 1 of IC604.

This is still not clear if it will fix the problems with the Pincushion circuit that I started with though. I am hoping that it will because I can see that the missing 25V on Pin 11 of IC250 is both the cause of the missing 6.5V, and it also connects to Q255, which is connected directly to Pin 2 of the Pincushion IC303. Pin 1 and 2 of IC303 are responsible for creating the parabola which effects Pincushion control, so if a bad voltage on Collector of Q255 effects the current present on its Base, then it could be the whole source of the problem.

I think the determination will be if Q203 is newly broken, or if it was already starting to fail before I got to the monitor. I think there is a case to be made that the 24V line might have damaged Q203 because it's connected to that supply. There was some failure on the 24V line before I started working on it which I fixed by replacing the fusible resistor. Probably caused by all the bad capacitors inside.

I ordered a couple replacement transistors which seems to be close enough to the ones that came out, but I won't get them until probably Monday.

I got my replacement transistors and installed them. I now have all the correct voltages on those places I was concerned about.

I also now have my parabola on Pin 7 of IC303, but it's not right. The voltage is something like 2X what the SM calls out, and it looks all messed up, especially if I try to tweak any of the Pincushion controls.

Not sure what would be specifically responsible for the parabola being too big; the voltage at this point is basically correct, so it's more like something in the current generation I guess. I think the issue must be in the controls for the Side Pin or near it. Nothing I can find from Service Manual voltages.

https://i.imgur.com/kCjS9WI.jpg

https://i.imgur.com/bJfs9P3.png

Yes, this is current-driven and/or generated.
this TEA IC are "class D" output (chopped), so a interference here is nrmal. But, if parabola is larger and image is ok, is nothing to worry (for example). Assuming image are distorted, something in the current path are wrong (good to re-check the TEA datasheet). For trying to reduce the parabola amplitude or gain.

Yes, this is current-driven and/or generated.
this TEA IC are "class D" output (chopped), so a interference here is nrmal. But, if parabola is larger and image is ok, is nothing to worry (for example). Assuming image are distorted, something in the current path are wrong (good to re-check the TEA datasheet). For trying to reduce the parabola amplitude or gain.


So I found that IC304, which generates the Horizontal Width Voltage, was regulating 22.5V and it wasn't changing with the potentiometer RV314. I swapped it for a new one and now I have most of my Pincushion controls back. It's definitely still a little hampered, but all the controls are now clearly doing something. There's still some kind of issue with the Side Pin controls as they jump around too much and too quickly. It's like when you have a bad potentiometer and you skip across dirty, broken carbon traces.

Except I know the pots are all fine because I removed all of them from circuit and tested them carefully for smooth continuity to the wipers from both sides.

I don't know what is possibly left to swap out. I have a new IC301, but the signals coming out of that IC seem fine. I also have new logic ICs for the switching stuff but, again, the switching seems fine.

I suppose that maybe it's just something sinking a little current and pulling down on the parabola a bit, so the ICs wouldn't have to be totally bad to cause an issue?

The main remaining issues is the Side Pin controls really. They don't quite work completely as expected.

The area I fixed:

https://i.imgur.com/ocWvzos.png

I removed IC301 and IC303, put in sockets and put in NOS ICs. That made the Pincushion controls just better enough that I can almost dial it in.

I found that the yoke is misaligned. It was twisted a little bit, so I went in and twisted it only to find that it's now slightly pointing up, so I'll have to go in and fix that.

This Monitor has a replacement tube in it that was put in sometime later in its life, which is good, but it seems the Sony Service place didn't take too much care when they oriented the tube. It's clear that they tilted it somewhat and then performed static convergence with it tilted in place.

So a multitude of issues... too bad, s&¨%¨$ can happen in the life of equipment...

So a multitude of issues... too bad, s&¨%¨$ can happen in the life of equipment...

Hahahaha. Yep, it's a bit of a endless pit. Honestly though, it's fine.

All of the remaining problems seem to be of the setup and calibration nature, which are all doable with the correct procedure. I'm happy to spend the time dialing everything in now that I know the electronics are functioning.

I was much more frustrated about it when I wasn't sure if it would ever work correctly and it was taking up space on my bench.

I've got other projects to work on!

Well I went in and pulled all the yoke wedges and set it up the best I could. There's still a tiny bit of weirdness in the upper corners, but not sure what I can do about it. I think it looks pretty good in usage, and it tracks color very well.

https://i.imgur.com/ilElBDI.png

Fantastic! :banana: :banana: :banana:
Seems great, even with these small distortion I bet it can pass easy with normal usage (will not much noticed)...

So after a little while using this monitor, I have realized that the HV regulation seems funny. I noticed it was bouncing in and out a little bit on the sides when it's cold, and sometimes.

As a test, I use the HV Regulation Pattern, which is a white box that flashes inside the middle of the screen. With this I discovered that the raster is stretching pretty significantly in the horizontal direction during flashes.

I began looking for a problem in the Horizontal, and subsequently discovered there's some problem with the 160V source. I see 155V on the 160V line. There must something blown up in there?

There are a few diodes and such between them, but I am wondering if anyone see anything as a smoking gun?

https://i.imgur.com/W8Tj5Je.png

You need to look for some voltage that changes when the width jumps. A steady 155 volts may just be due to component tolerances and not something failing.

+1 for watching voltages.
I can add, if PSU caps are good, I fear about the pulse caps in the HOT. Some monitors have switching for different resolutions (adding more cap for lower resolutions=lines), for tuning the flyback, and perhaps one can be "added" at these flash times. But, the image will be dim if this occurs (at the moment).
Also, if image srhinks at that time, can be a failing pulse cap. This can indeed produce/induce a high output voltage from flyback and produces a flash somewhere (depending about the severity of the failing cap).
Investigate it only if voltages are all stable at the flash times.

You need to look for some voltage that changes when the width jumps. A steady 155 volts may just be due to component tolerances and not something failing.

+1 for watching voltages.

Okay, I took readings at the 60V chopped voltage with feeds Q403 and to the collector of Q402, which I believe imparts the horizontal drive signal.

I also watched the 155V (160V) during the flash test.

Voltage stayed fairly steady at 155V during flash test. Dipped down maybe 200mV at most.

Both waveforms (Q402,403) stayed completely steady during the flash test. No movement whatsoever.

What was more interesting is that the waveform #2 which is supposed to be 660Vpk is more like 1.1kVpk.

This seems excessive. Although someone else has told me that 1kV is probably normal for a color monitor, even though the SM says 660kV. I don't know what to think about it.

I had to use a 100X probe for the readings on my scope, but both readings were taken with the same scope and probe on the same settings, so unless the scope or probe is somehow going to start misbehaving at a higher voltage, it's accurate (or service manual is wrong).

https://i.imgur.com/Emear5L.png

https://i.imgur.com/DqSmqHk.jpg

https://i.imgur.com/xwlyrCk.jpg

https://i.imgur.com/Ba0wQ8G.png


I can add, if PSU caps are good, I fear about the pulse caps in the HOT. Some monitors have switching for different resolutions (adding more cap for lower resolutions=lines), for tuning the flyback, and perhaps one can be "added" at these flash times. But, the image will be dim if this occurs (at the moment).
Also, if image srhinks at that time, can be a failing pulse cap. This can indeed produce/induce a high output voltage from flyback and produces a flash somewhere (depending about the severity of the failing cap).
Investigate it only if voltages are all stable at the flash times.

I measured all the capacitors in the path of the horizontal yoke and it's related circuitry (basically about 15 or so large film caps between the collector of H OUT transistor and the H Yoke coils). All capacitors are perfect, one cap is 10% out, and the rest are within 1%.

After getting it back together, I see a slight reduction of the horizontal breathing during the flash test. I also saw that the Pincushion settings had changed a small but noticeable amount.

I believe that I must have stumbled on a poor solder joint or something that was causing a little bit of issues with the Horizontal, and reflowing a lot of that section helped.

It's still not "perfect" though. I'm seeing two remaining flaws.

1) the top of the raster is still a little pinched inward under optimal settings, on the upper left-hand corner. not sure how to fix it, but the "Pin Up" control is all the way down to get it to the best possible setting. I would assume that the default setting for the Pin Up potentiometer is center, but I have to turn it all the way down to achieve the best outcome. This seems suspect to me, and possibly indicative of another issue. I traced the signal from the Pin Up control, and it runs to Q201 on the D board. This is labeled V RAMP. The collector of Q201 measures 11V steady instead of 11.4V, so I just kind of let it pass, but maybe it's worth checking the other voltages? I have it closed up, so somewhat reluctant to open it again for a long shot.

https://i.imgur.com/cz5g5Qb.png

2) the brightest whites don't get as bright as would expect them to before I start to get color smearing. This only seems to happen with the red, and that seems to be par for the course with 90s VGA monitors. I understand that red takes the most juice to drive or something, so it tends to crap out before the other colors.
However, it's happening right at the edge of what the SM states this monitor can handle, and I've generally seen it be okay with some headroom.

SM states it can handle 96-106 Nits, and I think the last time I did a white balance, I got it about 100ish Nits before it started to smear red towards the right of the whitest whites. It's not exactly dim, but it seems a little skimpy.

So my question to all here is: can I do anything to help with the red smearing, or is that just a function of the phosphors and nothing I can do? I'm new enough to this, and I've heard enough conflicting information about it to not conclusively know if it's fixable or not.

For example, could upping the value (or lowering the value) of a cap somewhere tighten up the color resolution at higher voltages?

The red bleeding is probably the CRT is weak. If it gets better with warm up & looks better with the brite & contrast reduced, CRT is most likely the suspect.
Quick test: Usually there is a low ohm resistor ( typ 1 ohm, 1W +-) in series with
the filament. Jump it out & see if it improves. That will increase the filament
from 6.3 to @ 8V & heat up the cathodes more. There is a very small risk
to this, its a last ditch way to get more life.

73 Zeno :smoke:
LFOD !

The red bleeding is probably the CRT is weak. If it gets better with warm up & looks better with the brite & contrast reduced, CRT is most likely the suspect.

It doesn't change with warm-up, and brightness has zero effect on it. I only see this when I push the contrast up high. There's a certain point at which if I turn the contrast knob up, the white solid areas ghost red to their right. I can manage at least ~103 Nits, which is already in line with what the manual says it can do (it says to lock the contrast down to 96 Nits +\- 10).

If I turn up the contrast to just before it starts to bleed, and I crank the brightness, it does not bleed; it goes right on getting more washed out until I can see retrace lines.

I have read in some places that this effect can appear when you have too much length to you cables or use an extension and is thus a bandwidth issue. I don't have an extension though, this set has a built-in cable.

If you turn up contrast just to where it does bleed, and then turn brightness way down, does it go away?

I don't know, but it's possible it has a beam current limiter that works to turn down contrast as you turn up brightness, and that's why the brightness can't cause smearing. Or it could be something else peculiar to this chassis that I can't think of.

Anyway, the red smearing is most often an indication that the red video output stage is saturating (going to the lowest possible output voltage), often due to the setup voltages required with a tired tube.

On the red problem it may be bad filtering on the @200 V supply for the
video outs. This is a common problem on all brands ! Symptoms are:
Left side normal, right side too brite.
Streaking.
Shading.
Jail bars.
Pix too bright.
Retrace lines in some or all of pix.
Looks like bad CRT
+ more I cant remember !
Poor px, just dont look right.Any combination of above.

Usually its a 4.7mfd or 10 mfd on the @200 V.
G-2 setting must be right also. Be sure you can extinguish or nearly so
the raster & have NO retrace lines.
Now back to the @200 V. On most the neg goes to GND. On some
the neg goes to the main B+ then there is another 'lytic neg to GRD.
That can cause width & jail bars, plus all the above.

Time for a bier :beer:
Zeno
LFOD !

On the red problem it may be bad filtering on the @200 V supply for the
video outs. This is a common problem on all brands ! Symptoms are:
Left side normal, right side too brite.
Streaking.
Shading.
Jail bars.
Pix too bright.
Retrace lines in some or all of pix.
Looks like bad CRT
+ more I cant remember !
Poor px, just dont look right.Any combination of above.

Usually its a 4.7mfd or 10 mfd on the @200 V.
G-2 setting must be right also. Be sure you can extinguish or nearly so
the raster & have NO retrace lines.
Now back to the @200 V. On most the neg goes to GND. On some
the neg goes to the main B+ then there is another 'lytic neg to GRD.
That can cause width & jail bars, plus all the above.



I tested C421 (10uf on the 200V) when I did the whole set and it looked good, but maybe it's a sneaky failure?

In any case it was one of few that wasn't replaced. I guess I can try that.

One interesting thing I found is that the far right side of the raster has bright fringing on the edges when the G2 is on the edge of making the raster glow, and it seems that things get weird if I push the brightness past that point. It's a really fine line where I can just barely get the brightness up past a dead black background and the image gets a lot worse and there's weird (and irregular) bright fringing on the right edge.

If I keep the G2 at right around dead black, the fringing goes away and the picture cleans up a lot (meaning I can get more headroom out of the contrast with a sharper picture). After I got it to that point, I was able to use a colorimeter and software to create a color profile that gamma corrects the monitor, so now the white point is correct and the picture is ramping the brightness correctly across the board. Looks a whole lot better now than it has at all so far.




If you turn up contrast just to where it does bleed, and then turn brightness way down, does it go away?


No, the brightness doesn't seem to have an effect on the red ghosting/bleeding.


I don't know, but it's possible it has a beam current limiter that works to turn down contrast as you turn up brightness, and that's why the brightness can't cause smearing. Or it could be something else peculiar to this chassis that I can't think of.


That could be true. It's got an automatic contrast control knob that I am supposed to set in the white balance procedure. It wants me to start off with everything super maxxed out and then use the contrast limiter to adjust it down. But this doesn't seem to work out when I follow what they want me to do. It seems to look much better when I ignore the brightness limiter and just turn the G2 down and the sub contrast down until everything is reasonable.

]Anyway, the red smearing is most often an indication that the red video output stage is saturating (going to the lowest possible output voltage), often due to the setup voltages required with a tired tube.

It might be that, but also I might just be hitting some limits and it's a combination of things. As it stands now, it is plenty bright to use. I'm mostly now just concerned with the weird bright fringing on the right side of the screen. It might be worth replacing that 10uf cap on the 200V that measured good just in case.

Try to measure the DC voltages of the CRT cathodes. This can indirectly *sometimes* make a clue. If DC reading of the red cathode differs too much from others, something are ocurring. For example, a too low red cat. voltage can make the output stage saturating (on peaks/high luminance). More easy on monitors, since it have less dynamic range than a regular TV since it operates with lower voltages due to larger bandwidth (for not over dissipating).

Try to measure the DC voltages of the CRT cathodes. This can indirectly *sometimes* make a clue. If DC reading of the red cathode differs too much from others, something are ocurring. For example, a too low red cat. voltage can make the output stage saturating (on peaks/high luminance). More easy on monitors, since it have less dynamic range than a regular TV since it operates with lower voltages due to larger bandwidth (for not over dissipating).

Okay. I have done a number of different things.

I checked the cathodes, and they have a +50VDC offset. Not entirely sure why, but I think it might have something to do with the multisync nature of the monitor in that it operates the cathodes at a floating voltage. Perhaps it has something to do with the way that it overlays the video on top of the raster. Not sure, it's a little above my head at the moment.

But for whatever reason, it does float the voltage and it relies on the G2 to G1 to raise the pedestal of the image to the right level.

That means I could potentially push the whole voltage level down a bit and get more headroom.

I also bought a slightly higher bandwidth version of the video amp IC (it can do 100MHz vs 70MHz), and tried it out.

There were a couple takeaways from that. First, I had to install a green drive pot to match the red and blue because the new video amp has slightly different gain characteristics that don't work well with the existing circuit. I just matched the values of the other two and that seems to be okay.

Secondly, I started messing with the 33 ohm resistors on the TE pins of the video amp inputs. I understand that this is a HF compensation method and that it will alter how fast the video amp can function. However, changing these values also seems to have an effect on the clipping of the video amps.

You can see them on the right side of the video amp IC:

https://i.imgur.com/mnG4BK9.png

Raising the values of the red and blue channels, I am able to get more total brightness out of the raster without clipping from the video amp. I think there's something besides the total swing of the video signal on the amp that is contributing to the clipping. It seems like the TE pins are effecting the biasing of the IC as well.

The internal schematic of the Video Amp IC:

https://i.imgur.com/N7xjt0V.png

Unfortunately, the new amp doesn't seem to play nicely with the current circuit in other ways as it seems to have a different DC offset, and it ends up too dim when I adjust the G2 for proper black levels. Basically, I think it ends up with the pedestal too high up, and then the G2 has to be lowered a lot to compensate, which lowers the G1 G2 relationship and the overall luminance goes down.

I think after that, I realized something interesting the service manual. The color balance procedure has you max out the bias controls to start, and then to pull them down to balance. That means that you are effectively pulling the pedestal all the way down and then selectively pulling guns up to reduce their effect on the background. This IIRC is not how it's done in other monitors and TVs I've worked on; typically, they have you start in the middle or at the bottom and then work your way up. I have to assume that they are considering zero volts as the brightest possible bright, and this monitor expects that to be between 45-50V. Black levels are supposed to be about 90V and it's supposed to swing around 45V in the middle.


In any case, I'd love to figure out how to redesign the bias network to use the VPS10 (100MHz part) in this monitor. From my testing, it was much, much crisper of an image (at a similar level of brightness to the old video amp), even though it turned out dimmer with the present circuit.

This is the bias network circuit if anyone has any suggestions. I guess I would assume I would have to mess with these resistors in the voltage divider for the 180V to the bias controls. The new video amp looks like it maxes out at like 106V instead of 90V or something, so I'd need to lower the DC offset of the video signal by about that much. I'd still have the bias controls to do the fine tune, but it's apparently too far out.

https://i.imgur.com/Zf9NQtU.png

Okay. I have done a number of different things.

I checked the cathodes, and they have a +50VDC offset. Not entirely sure why, but I think it might have something to do with the multisync nature of the monitor in that it operates the cathodes at a floating voltage. Perhaps it has something to do with the way that it overlays the video on top of the raster. Not sure, it's a little above my head at the moment.

But for whatever reason, it does float the voltage and it relies on the G2 to G1 to raise the pedestal of the image to the right level.

That means I could potentially push the whole voltage level down a bit and get more headroom.

I also bought a slightly higher bandwidth version of the video amp IC (it can do 100MHz vs 70MHz), and tried it out.

There were a couple takeaways from that. First, I had to install a green drive pot to match the red and blue because the new video amp has slightly different gain characteristics that don't work well with the existing circuit. I just matched the values of the other two and that seems to be okay.

Secondly, I started messing with the 33 ohm resistors on the TE pins of the video amp inputs. I understand that this is a HF compensation method and that it will alter how fast the video amp can function. However, changing these values also seems to have an effect on the clipping of the video amps.

You can see them on the right side of the video amp IC:

https://i.imgur.com/mnG4BK9.png

Raising the values of the red and blue channels, I am able to get more total brightness out of the raster without clipping from the video amp. I think there's something besides the total swing of the video signal on the amp that is contributing to the clipping. It seems like the TE pins are effecting the biasing of the IC as well.

The internal schematic of the Video Amp IC:

https://i.imgur.com/N7xjt0V.png

Unfortunately, the new amp doesn't seem to play nicely with the current circuit in other ways as it seems to have a different DC offset, and it ends up too dim when I adjust the G2 for proper black levels. Basically, I think it ends up with the pedestal too high up, and then the G2 has to be lowered a lot to compensate, which lowers the G1 G2 relationship and the overall luminance goes down.

I think after that, I realized something interesting the service manual. The color balance procedure has you max out the bias controls to start, and then to pull them down to balance. That means that you are effectively pulling the pedestal all the way down and then selectively pulling guns up to reduce their effect on the background. This IIRC is not how it's done in other monitors and TVs I've worked on; typically, they have you start in the middle or at the bottom and then work your way up. I have to assume that they are considering zero volts as the brightest possible bright, and this monitor expects that to be between 45-50V. Black levels are supposed to be about 90V and it's supposed to swing around 45V in the middle.


In any case, I'd love to figure out how to redesign the bias network to use the VPS10 (100MHz part) in this monitor. From my testing, it was much, much crisper of an image (at a similar level of brightness to the old video amp), even though it turned out dimmer with the present circuit.

This is the bias network circuit if anyone has any suggestions. I guess I would assume I would have to mess with these resistors in the voltage divider for the 180V to the bias controls. The new video amp looks like it maxes out at like 106V instead of 90V or something, so I'd need to lower the DC offset of the video signal by about that much. I'd still have the bias controls to do the fine tune, but it's apparently too far out.

https://i.imgur.com/Zf9NQtU.png

Perhaps the VPS10 have less gain, setted internally. If is possible to raise the gain without altering the bias (perhaps a divider from the local supply to ground). But not entirely promising, since the IC have internal emitter R. Better is to provide more gain in the preamp.

About cathodes, ia relatively common to have this type of pedesta clamping, direct to the cathodes; the DC restoration being here and even in ultra hi-end and low end CRT monitors. What interesting, is like a return to the 1940's or suchlike (a simple diode DC restorer in the CRT section).

Perhaps the VPS10 have less gain, setted internally. If is possible to raise the gain without altering the bias (perhaps a divider from the local supply to ground). But not entirely promising, since the IC have internal emitter R. Better is to provide more gain in the preamp.


I took a couple of scope readings of the red cathode as a baseline, while viewing a color bars.

I started with VPS07T installed and got it as bright as possible with true black pedestal and no smearing caused by saturation of the amp.

The VPS07T was showing about 58Vpkpk with black slightly over 100V, and the whites at 45V.

Then I installed VPS10 and took the same measurement first without changing anything.

The VPS10 was showing about 48Vpkpk with the black at about 96V and the whites at about 50Vpkpk.

So at the same settings, the gain of the VPS10 swings a little lower, resulting in a lower voltage for black and higher peak voltage.

Then, I color balanced the monitor with VPS10 installed, and I was able to increase the swing all the way to 60Vpkpk, but to get it there, I have to peak the manual brightness control and lower the G2 such that the pedestal is still below the level of the VPS07T. It's not a huge difference, voltage-wise, but it seems to make a big difference in the overall brightness and the color linearity.

The final scope reading with the VPS10 tuned the best I can get it is about 97V for black, and 40V for whites. Any higher contrast than that and the colors start to clip and I get smearing.

So it seems that the black level (the pedestal) is about 6V lower for the VPS10 than the VPS07T, and that's what I'd have to find a way to shift.

Currently, the only thing I can do to shift the whole DC offset range is to lower the bias controls, but if I do that, then image smears at a much lower drive level. I think the output circuit is somehow designed to have the bias controls at the top of their travel, and the G2 is supposed to be set with the bias as high as possible. The Service Manual instructions state to do this, and it seems to be correct.

Aside from the Drive, Amp, and Bias sections, there is the preamp IC, but I don't have a datasheet for it, nor can I find one anywhere on the net. Its a CXA1209P, a Sony IC.

Perhaps the answer is to alter values to the blanking pins or something?

https://i.imgur.com/fR6MwId.png

The bright pin have a fixed divider. Perhaps the IC have a pedestal clamp, independent of the fact of it being clamped at the CRT? Perhaps it have, for having more defined levels to the vide out.
So, *perhaps* altering the bright pin voltage the pedestal will alter. Is worth investigating.

The bright pin have a fixed divider. Perhaps the IC have a pedestal clamp, independent of the fact of it being clamped at the CRT? Perhaps it have, for having more defined levels to the vide out.
So, *perhaps* altering the bright pin voltage the pedestal will alter. Is worth investigating.

Thanks. This does seem to agree with what I have seen. I get a better picture and more total contrast if I crank up the brightness knob on the front and I turn down the G2.

Probably the best solution is to build a -100V power supply and pull the G1 negative, but I don't have the parts for that right now. I am thinking about trying it though.

In the intervening time, I managed to tweak the resistors on the TE pins and eke more contrast out of the VPS10 IC. I now have it to about the same level of brightness as the VPS07T, but it's much, much crisper and there isn't any red smearing anymore like the VPS07T had.

Totally worth it.

Interesting. In my 29" TV, even having a AKB circuit feedback, I prefer the image with somewhat low g2 setting. Also with one of my low-end monitor.

BTW: If the pin #1 of the CXA not bring the desired range, or maxed out, perhaps adjusting the divider at the pin #2? Well suggestively labelled (BRIGHT)... If you already not played with this yet

Interesting. In my 29" TV, even having a AKB circuit feedback, I prefer the image with somewhat low g2 setting. Also with one of my low-end monitor.


At least in this particular monitor, when I change the bias controls or the brightness, it shifts the DC offset of the whole video signal up and down.

The G2 doesn't demonstrably effect the DC offset, it just makes everything brighter on the screen, including the black becoming grey.


In other TVs and monitors, it has been my experience that I get the clearest, brightest picture by turning the color bias controls and brightness control all the way down and cranking up the G2 to compensate. My understanding is that this pulls the video signal way up away from G1 and shrinks the spot size, resulting in a sharper image. But in this monitor, if I try to do this, I get blooming and smearing at a much lower total luminance than if I do it the other way around.

I think maybe the Automatic Contrast Limiter is having some effect in the circuit that prefers it to be set that way.



BTW: If the pin #1 of the CXA not bring the desired range, or maxed out, perhaps adjusting the divider at the pin #2? Well suggestively labelled (BRIGHT)... If you already not played with this yet

I haven't messed with the Bright pin yet, but it did seem simple enough to alter the divider there.

Honestly, I'm thinking my best gains might be to pull the G1 down to about -100V and see if I can shrink the spot size that way. That will also allow me to raise G2 and get more brightness without increasing the swing on the video amp

I'm working on a circuit I can use to convert the +180V B+ to -100V for the G1. It should be high enough impedance that the load won't be an issue I think.

Indeed a lot if not the majority of CRT can benefit from a different bias for the spot size (for a better one), but I believe some ones having already good focus, and it can be "too good" especially for normal resolution TV's.
I remeber old_tv-nut mentioning this issue in this thread: http://videokarma.org/showthread.php?t=276967
About normal TV having incredible focus/spot size for the given size of phosphours, is possible to saturate the center of the ones, if I understand well, generating different color saturation.

I tempted to make this with my Sony F99 chassis monitor (and it for sure will be benefited by), but the G2 in these are monitored and automatically controlled by the µcontroller and a AKB system, amplified by a HV low current transistor. It blanks the screen if one messes with the voltages too much.

Indeed a lot if not the majority of CRT can benefit from a different bias for the spot size (for a better one), but I believe some ones having already good focus, and it can be "too good" especially for normal resolution TV's.
I remeber old_tv-nut mentioning this issue in this thread: http://videokarma.org/showthread.php?t=276967
About normal TV having incredible focus/spot size for the given size of phosphours, is possible to saturate the center of the ones, if I understand well, generating different color saturation.


I think the general problem is that you get moiré patterns if your spot size is too small for the slot mask. It seems to be less of an issue for aperture grills.

I've never read about the phosphor issues, but I reading that thread you linked it sounds like they are talking about old Zenith's, which were using different phosphors and such. It's also possible to mitigate color linearity issues by tweaking the components controlling the gain for individual colors, if not a bit tedious.


I tempted to make this with my Sony F99 chassis monitor (and it for sure will be benefited by), but the G2 in these are monitored and automatically controlled by the µcontroller and a AKB system, amplified by a HV low current transistor. It blanks the screen if one messes with the voltages too much.

Sounds about right. The later Sony CRT PC monitors are extremely complex. It makes me sad to think how incredible they used to be and what they are doing now. Basically just the PlayStation and their CCD fabs.