First a little background. I got this set in about 1992, and used it sporadically for about 12 years before mothballing it in storage. It worked very well and had a bright tube when I got it, and I didn't put a lot of wear on it myself.

I got it out of storage recently for a project, and it needed to have basically all of the electrolytics replaced. Several of them had corroded away to nothing, and all but a few were way, way out of spec and drying out.

So I finished a full recap, and set it up as per the service manual a

nd the Sams.

It works okay, and is still pretty bright, but it's got a few lingering issues that I'm not sure what to do about.

1) In some material (not all), there is horizontal lines in the colors. This seems to be stronger when I turn down the brightness. So far, it only happens with one of the DVDs I tested. The lines are strongest in the Red, but I have also noticed them in Blue. I don't (or can't) see these lines in other things I have tested in the same DVD player (so far). The DVD that does show these lines seems fine on other TVs.

2) I followed the setup instructions, and it says I should set the BKG dials at halfway, the DRIVE dials at full, and adjust a crosshatch for best grey at the BKG dials. The BLUE crosshatch comes up first, but it's only the vertical lines, not the horizontal lines which take a lot more background to make appear. Red and Green do not appear to have the same issue, and the horizontal lines do appear as bright as the vertical lines. Because of this issue, I was unable to set the white balance this way, and I had to use a black background and just do the whole screen to grey. This eventually worked after a whole lot of back and forth and looking at greyscale images, but I can't help feeling like this issue with the Blue being much stronger vertically is a problem, especially since it doesn't effect the Green or Red.

I was thinking maybe I should try replacing the BKG and DRIVE transistors and see how that goes. I don't know what else I could try. This is the output section of the schematic:

https://i.imgur.com/3wZx4rK.jpg



3) The Sam's references a "Beat Pattern," when adjusting the 4mHz trap. It wants me to adjust the fine tuning on strong signal until I get a "beat pattern," and then turn a pot until that goes away. I don't know what a beat pattern is. Any help with that?

4) The Sam's also wants me to use a sweep generator for some of the setup stuff. I don't have one. I have a scope, a signal generator, and a pattern generator. Can I use the function generator in place of a sweep generator in this fashion?

https://i.imgur.com/HdQTo7V.jpg

5) The Horizontal Oscillator seems flakey. I followed the instructions, which is to ground the transistor on the Oscillator and adjust the control until the image stops floating, but I couldn't really get it to stop completely. I could get it right to the point when it starts to drift in the other direction, but it floats around enough that it will move back and forth by itself if I leave it alone. I don't know how much of an issue this is, but I thought if it was, I might need to replace a transistor, or maybe a pot with more turns will allow me to get it more accurate?

https://i.imgur.com/WA6aBtr.jpg


Thanks

1) Don't understand what "horizontal lines in the colors" means. Can you post a picture?
2) No idea why blue vertical lines are stronger than horizontal lines. Maybe a shorted coil?
3) A "beat pattern" means stripes or herringbone interference in the picture. If your signal has audio content, the pattern will move along with the audio content. You should easily recognize it as something that doesn't belong there.
4) If the setup requires a sweep generator, you must use a sweep generator. This is the case for IF alignment and color alignment if the service instructions say so. The good news is that these seldom change, especially not in solid state sets, as long as components have not failed, so the best bet is to skip alignment and see if the picture and sound are OK without it.
5) The H oscillator will float a bit normally just from random voltages in the chassis. The important thing is that it's not skewed entirely one way or the other. Going back and forth a bit is fine. When you remove the ground, it should lock up, and that's all you need.

Thanks for the reply

1) Don't understand what "horizontal lines in the colors" means. Can you post a picture?

This is the best I can do. The horizontal lines through the characters are what I'm talking about. They appear in different shades depending on the color they run through. It only (so far) happens with this DVD.

https://i.imgur.com/u5gjc2B.jpg


2) No idea why blue vertical lines are stronger than horizontal lines. Maybe a shorted coil?


That doesn't sound good. I wouldn't know how to test for that either.



3) A "beat pattern" means stripes or herringbone interference in the picture. If your signal has audio content, the pattern will move along with the audio content. You should easily recognize it as something that doesn't belong there.


Ok. I didn't see anything like that. The instructions say that such a pattern should appear as I use the fine tuning and move it away from the station. When I do that, it goes black and white counterclockwise, and turns to snow as I go clockwise. There doesn't seem to be much of a transition either way

4) If the setup requires a sweep generator, you must use a sweep generator. This is the case for IF alignment and color alignment if the service instructions say so. The good news is that these seldom change, especially not in solid state sets, as long as components have not failed, so the best bet is to skip alignment and see if the picture and sound are OK without it.



Well, I had to replace a lot of caps. I think this set runs pretty hot due to the small size and almost all of them were toast. So I guess it's okay, but I thought maybe replacing the caps would mess with the RF.


5) The H oscillator will float a bit normally just from random voltages in the chassis. The important thing is that it's not skewed entirely one way or the other. Going back and forth a bit is fine. When you remove the ground, it should lock up, and that's all you need.


Okay, thanks. It made it seem like in the Sams that there would be a spot that it locks as I mess with the pot. It's good to know it doesn't matter. I definitely got it so it isn't skewed at least.


I realized there was one other thing I was wondering about:

6) The focus on this set is handled by moving a jumper wire from a resistor to one of three positions. There's zero volts, something like 130V, and 530V. It seems like zero volts is too little, and 530V is too much, but 130V doesn't look to my eye to be quite right either. Is it crazy to just put a variable resistor between 530V and ground and just tune it in like I would on a set with a focus pot?

Thanks again!

A little at a time...... Make as good a B&W pic as you can. Forget
the color for now.

Be sure the cap on source #7 ( 4.7mfd ?) has been changed.
Put real content NOT a generator on it.
Turn off all auto color controls & color control all the way down.
Contrast & bright about 3/4 up.
Be sure you can turn the brite down all the way down to no pix or
very dim pix. If not turn down G-2 a little.
If it looks like it has bad convergence adj the H-STAT control.

Now go to manual & put R-B-G controls at the start point, Make the
pix as B&W as you can. Then we can take it from there.

BTW the lines you see are the phosphor stripes.
The CRT is a low focus type & moving the jumper seldom makes a difference.
You could use a pot but use a 1 watt & be sure it runs cool !

73 Zeno:smoke:
LFOD !

1) only happens with one DVD? Then it's the DVD. Looks to me like the DVD may be a copy of a videotape that had some defects.

2) Since there are similar coils in R,G, and B circuits, you can compare them. One way to detect a shorted coil would be with an ohmmeter, but the low resistance values may be hard to measure accurately. Another thing you could try is connecting a short wire across a coil in the red or green circuit and see if it gives the same effect as you see in the blue. If it does, then try shorting the corresponding blue coil to verify that the added short doesn't change the problem; in other words, the coil in the blue section was already shorted. Of course, I am only guessing about the possible cause, and you may find that the coils are OK and the problem is something else.

3) If you're not seeing a beat pattern, the best bet is that the adjustment is already optimum, so just leave it alone.

4) Caps that would affect the alignment are small pf values associated with IF coils/transformers, and seldom fail, so are not usually replaced when re-capping. Typically needing recapping are electrolytics and paper caps with much larger values, like nanofarads (thousands of picofarads) and upward to microfarads. If the picture and general operation of the set is OK, alignment is not needed, and is only an educational exercise.

A little at a time...... Make as good a B&W pic as you can. Forget
the color for now.

Be sure the cap on source #7 ( 4.7mfd ?) has been changed.
Put real content NOT a generator on it.
Turn off all auto color controls & color control all the way down.
Contrast & bright about 3/4 up.
Be sure you can turn the brite down all the way down to no pix or
very dim pix. If not turn down G-2 a little.
If it looks like it has bad convergence adj the H-STAT control.

Now go to manual & put R-B-G controls at the start point, Make the
pix as B&W as you can. Then we can take it from there.


Ok. I'll start over with it. The yoke got loose at some point while it was in storage so my purity was pooched and I had to mess with it. I got it to a "decent" place, but it could be a little better. It's sorta difficult when pretty much everything needed to be adjusted somewhat to know what to work on first.



The CRT is a low focus type & moving the jumper seldom makes a difference.


Yes, they didn't help, but the "middle" value, which is about 200V is the factory setting, and it's the closest to good focus out of the three. The higher voltage is about 500V, so I figured the most ideal spot would be somewhere between 200-500V, and pot would be useful.

You could use a pot but use a 1 watt & be sure it runs cool !


Does that mean I need to get a 500V, 1 watt pot? It's going to be pretty big, also expensive. Not sure this set is worth that, but it might be interesting as an experiment anyway. I found this one on mouser: https://www.mouser.com/ProductDetail/72-357B2102MAB251S22

1) only happens with one DVD? Then it's the DVD. Looks to me like the DVD may be a copy of a videotape that had some defects.

Good point.

2) Since there are similar coils in R,G, and B circuits, you can compare them. One way to detect a shorted coil would be with an ohmmeter, but the low resistance values may be hard to measure accurately. Another thing you could try is connecting a short wire across a coil in the red or green circuit and see if it gives the same effect as you see in the blue. If it does, then try shorting the corresponding blue coil to verify that the added short doesn't change the problem; in other words, the coil in the blue section was already shorted.

By coils, you're referring to the coils on the neck board attached to the RGB output transistors, correct? It's weird, but the service manual and the Sam's both give different values for them, so I'm not actually sure which they should be. I could pull them and measure them. I have an LCR meter. The Sam's says 1.5uH, the Sony manual says 8.2uH. Go figure.

I am only guessing about the possible cause, and you may find that the coils are OK and the problem is something else.


Yeah, that's why I was considering just getting a few new output transistors and replacing them. I'm sure I can find something beefier that will at least be more robust, even if it doesn't fix anything. Maybe a Motorola MPSU10 or something?

3) If you're not seeing a beat pattern, the best bet is that the adjustment is already optimum, so just leave it alone.


Makes sense.

4) Caps that would affect the alignment are small pf values associated with IF coils/transformers, and seldom fail, so are not usually replaced when re-capping. Typically needing recapping are electrolytics and paper caps with much larger values, like nanofarads (thousands of picofarads) and upward to microfarads. If the picture and general operation of the set is OK, alignment is not needed, and is only an educational exercise.

Yeah, the yoke moved around in storage and the purity was garbage. I had to move it around a bit, and then I realized it needed a bit of fine tuning. I'm tyring to sort out what might still be an electrical problem with what's just in need of adjustment.

Thanks everyone. I'm probably going to place another order to Mouser this week, so I'm trying to finalize if I need anything else for this particular project.

"By coils, you're referring to the coils on the neck board attached to the RGB output transistors, correct? It's weird, but the service manual and the Sam's both give different values for them, so I'm not actually sure which they should be. I could pull them and measure them. I have an LCR meter. The Sam's says 1.5uH, the Sony manual says 8.2uH. Go figure."

I mean any of the six coils that are the same in R,G, and B: L702, 703, 704, 302, 306, 307.

I just noticed that C701 (blue channel) is 560 pf and the correspong R and B caps are 390 pf. This could be making the difference, though I'm not sure why they would do that.

I just noticed that C701 (blue channel) is 560 pf and the correspong R and B caps are 390 pf. This could be making the difference, though I'm not sure why they would do that.

Well, thinking about it, the only difference I can see is that the RGB drive signals are all different voltage levels as they come out of demod. Red is 4V, Blue is 5.8V, and Green is 1.5V. I've seen this arrangement (not necessarily the exact same voltages) in other sets before, although I don't understand why it is. Perhaps related to that somehow?

Those differences in color difference signal levels with a rainbow generator are because the R-Y and B-Y signals in a normal video signal are scaled down before modulation on the color subcarrier to prevent overmodulation on particular colors. With a color signal of real color bars or program video, those differences in gain restore the final R, G, and B signals to the right level once the luminance signal is added. For example, full amplitude saturated green bar has luminance of 59% of white, so the G-Y only has to make up 41% to turn green on completely. (The final values of R, G, and B for white may not be equal due to differences in R, G, and B phosphor efficiency, plus NTSC sets typically had increased R-Y gain to make up for the yellowish modern green phosphor.) Since the rainbow pattern consists of constant amplitude subcarrier, it does not have prescaling depending on hue, and therefore the gain differences in the color difference demodulators show up.

It's the copyguard causing the issues, they insert a 180 phase inversion in so many horizontal lines to thwart the chroma AFC in the color under VCRs. Look at the signal on a pulse cross monitor and turn the color up. Your Sony is slow to respond to the phase inversion

Those differences in color difference signal levels with a rainbow generator are because the R-Y and B-Y signals in a normal video signal are scaled down before modulation on the color subcarrier to prevent overmodulation on particular colors. With a color signal of real color bars or program video, those differences in gain restore the final R, G, and B signals to the right level once the luminance signal is added. For example, full amplitude saturated green bar has luminance of 59% of white, so the G-Y only has to make up 41% to turn green on completely. (The final values of R, G, and B for white may not be equal due to differences in R, G, and B phosphor efficiency, plus NTSC sets typically had increased R-Y gain to make up for the yellowish modern green phosphor.) Since the rainbow pattern consists of constant amplitude subcarrier, it does not have prescaling depending on hue, and therefore the gain differences in the color difference demodulators show up.

Ok thanks. So those voltages are assuming an NTSC test pattern. I'm sure it says that in the Sam's and I forgot. There's a lot to remember

It's the copyguard causing the issues, they insert a 180 phase inversion in so many horizontal lines to thwart the chroma AFC in the color under VCRs. Look at the signal on a pulse cross monitor and turn the color up. Your Sony is slow to respond to the phase inversion

I see. That's really interesting. It's good to know what was causing that. Interesting also that it only shows up one DVD out of all that I've tried. It's not nearly the newest DVD I have either.

But actually, that was a separate issue. old_tv_nut was trying to help me figure out why the Blue vertical lines seem to be so much stronger than the Blue horizontal lines when displaying a crosshatch pattern from a B&K pattern generator. The Red and Green seem to come up in equal intensity.

He was suggesting that the capacitor in the Blue area seems to be a different value for some reason and that might be why.

I'm also still trying to figure out what I should order if I wanted to bodge a focus pot into the set. The optimal focus seems to fall somewhere in between the 200V setting and the 500V setting, so I wanted to get a pot and see how good I can get it. It was recommended I get a 1 watt pot, but 500V 1 watt pots are *huge*. The best I can find is like this https://www.mouser.com/ProductDetail/Vishay-Spectrol/357B2202MAB251S22?qs=IpR5h64PZJlrJ4hfGtyjeA%3D%3D

I found a bunch of smaller 1 watt trimmers, but they are rated for like 400V.

You may use the 400V trimmers in theory, if you can make a voltage divider. Is possible since you have found that the ideal voltage are between a interval, so the initial 200V can be at the resistive divider, and the pot at top (like most focus dividers). Of course, a real higher voltage device is safer.

You may use the 400V trimmers in theory, if you can make a voltage divider. Is possible since you have found that the ideal voltage are between a interval, so the initial 200V can be at the resistive divider, and the pot at top (like most focus dividers). Of course, a real higher voltage device is safer.

Thanks! I figured as much. I was looking at the available devices and I think I'm going to buy the 500V pot. It's about $20, and I can reuse it in the future. I will tweak the pot until I find the right spot and then put a fixed voltage divider at the correct values and leave it.

That way I can take it out and use it again. Also, there isn't really a good spot to put such a device when it's closed, so it's better if I just put some 1 watt resistors in it's place.

I thinking about now how I would wire that in. Should I put in between the 500V source and ground? Seems like I should just use the F1 spot for the far side of the pot because it's zero volts.

Yes, you can connect one end to F1.
From your link, it seems to be a 2k pot. Too low value; will load too much the 530V supply.
You can choose a pot >1M ohm, since the focus grid almost don't drain current.
In fact, I use a 12M pot I found in a local electronic store when optimizing focus.

Yes, you can connect one end to F1.
From your link, it seems to be a 2k pot. Too low value; will load too much the 530V supply.
You can choose a pot >1M ohm, since the focus grid almost don't drain current.
In fact, I use a 12M pot I found in a local electronic store when optimizing focus.


Thanks Alex,

I looked on Mouser and Digikey, but the highest thing I can find in stock is a 1Mohm pot. It's a 2W bournes unit: https://www.mouser.com/ProductDetail/Bourns/3852A-282-105AL?qs=HA4U26RXMPsKoe76JZfFDA%3D%3D

There's others in stock, but they all seem pretty similar.

Do you think 1M would be fine?

Seems to be perfectly fine.

So I finally got the 1 MEG pot to try fine tuning the Focus Voltage.

I hooked up the Focus (F0) to the wiper, and then I hooked up one end of the pot to the F2 terminal (500V), and the other end to F1 (Ground).

To my surprise, the focus looks the clearest when it's all the way at 500V, but it looks better with the pot hooked up this way than it does with the Focus (F0) hooked up directly to F2

I'm assuming here that this is because I have essentially have a 1 Meg resistor hooked up between the 500V source for the Screen pot and GND

This seems to have the effect of lowering the overall brightness quite a bit (meaning I then have to turn up the Screen to compensate), but it then gives me a lot more headroom for the Picture control, and I can turn up the Contrast (Picture) more before the whites start to bloom.

Is there some reason not to just hook up a 1 Meg resistore between the 500V source and ground at this point?

Thanks

The potmeter was there for factory adjustments to compensate for CRT variations, but it seems that you got a CRT with optimum focus voltage just right with the supply value, so is not really necessary if is working well at the moment. The issue will be only in the future, if CRT changes a little, then will not have how to readjust it.
That said, probably the CRT stands with the current value for years.

The potmeter was there for factory adjustments to compensate for CRT variations, but it seems that you got a CRT with optimum focus voltage just right with the supply value, so is not really necessary if is working well at the moment. The issue will be only in the future, if CRT changes a little, then will not have how to readjust it.
That said, probably the CRT stands with the current value for years.


I got a little fatigued on this project and put it aside for awhile, but I have a moment to look at it again, and I realize that the focus could still be better if I have to admit.

I looked into other ways to improve focus, and I ran across a thread on this forum talking about lowering the G1 voltage (ideally making it negative) to improve focus.
(https://www.videokarma.org/showthread.php?t=274214)
Looking at my schematic, it looks like the G1 is set to 38.2V, and the G2 is set to 307V. The focus range is 0-530V, but it's got those "steps."


Do you think perhaps I could improve focus by sticking a pot on the G1 and lowering it closer to ground?

Wondering also if it would damage anything to do so.

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

You can use the lens effect and reduces Vg1, but you can need to compensate raising the Vg2 (screens), and also needs more video amplitude, if you wanto to maintain same contrast ratio. Perhaps a little loss of contrast can be compensated for taste sake with the sharper picture.

For me, for example, my delta-gun TV, I swears that it have more bright when it are critically focused. I not measured it, but I have a DMM with luximeter that I already measured some TV brightness, including that. Someday I measure it.

But I assume that being a side product (impression caused) of the focusing.

You can use the lens effect and reduces Vg1, but you can need to compensate raising the Vg2 (screens), and also needs more video amplitude, if you wanto to maintain same contrast ratio. Perhaps a little loss of contrast can be compensated for taste sake with the sharper picture.

For me, for example, my delta-gun TV, I swears that it have more bright when it are critically focused. I not measured it, but I have a DMM with luximeter that I already measured some TV brightness, including that. Someday I measure it.

But I assume that being a side product (impression caused) of the focusing.

I think I want to tweak it and see how it effects things just for fun and as an experiment. I have lots of old TVs, so this is just fun for me, nothing too serious.

Would you mind confirming the tube neck pins for me?

It looks like the heater is 105V. That's very high compared to others I have worked on. At 105V pkpk that's something like 37V RMS? Seems very high for a heater, although maybe that's because it's a low voltage focus tube?

Seems like the G1 is 38.3V, the G2 is ~300V and the Focus is 0-500V?

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

It's a 6.3 V AC heater, but floating at 105 V DC so the DC on the heater is close to the DC voltages on the cathodes.

It's a 6.3 V AC heater, but floating at 105 V DC so the DC on the heater is close to the DC voltages on the cathodes.


That makes sense. So it's a 6.3 VAC heater with a 105VDC offset then?

That makes sense. So it's a 6.3 VAC heater with a 105VDC offset then?
yes - but double check the AC value because I'm not 100% sure.

I think I want to tweak it and see how it effects things just for fun and as an experiment. I have lots of old TVs, so this is just fun for me, nothing too serious.

Would you mind confirming the tube neck pins for me?

It looks like the heater is 105V. That's very high compared to others I have worked on. At 105V pkpk that's something like 37V RMS? Seems very high for a heater, although maybe that's because it's a low voltage focus tube?

Seems like the G1 is 38.3V, the G2 is ~300V and the Focus is 0-500V?

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

Old_TV_nut pointed about the floating heather, and your annotations for other pins are exact.

Old_TV_nut pointed about the floating heather, and your annotations for other pins are exact.

Thanks.

I'm looking at the schematic and trying to determine how best to lower the voltage of G1.

I could either just tie it directly to ground and see how that looks, or I could try to stick a pot in the circuit somewhere to create another voltage divider and lower the voltage somewhat (maybe halfway to start).

I have been trying to figure out how they derived 38.3V from this circuit.
I can see there's a 68K resistor on the far side of the circuit (which I guess forms an RC network with C705), and then there's the 530V source running through a 500k pot and a 330k resistor.

The middle Focus voltage is 208V, which works out correctly at point "219" on the schematic. (530V through the center of a voltage divider 330k,500k works out to ~210V)

So then I have a 210V source that hits a voltage divider at 330k,68k which works out to ~36V, which is basically correct.

So my plan is to replace R721 (68k) with a pot and take it down to like 10V and see how that looks.

Do you think I will run into any issues with the RC network R721,C705?

You can experiment to ground for first tests, since is easy to make. 38V sounds like not a extreme difference, even taking into account the low V focus tube. In any case, when you readjust the g2, bright and contrast to compensate, the cathode voltages will change. No big deal, unless video amp are out of range.

You can experiment to ground for first tests, since is easy to make. 38V sounds like not a extreme difference, even taking into account the low V focus tube. In any case, when you readjust the g2, bright and contrast to compensate, the cathode voltages will change. No big deal, unless video amp are out of range.

Meaning that I'll have to re-white balance the set, correct?

If it mistracks (probably a little), but watch first if beam focus suffices with 0V, or if needs more voltage (negative).

Just one curiosity, about this subject (a "side topic" related), if one knows about it:
Some B&W sets have g1 driven and cathode grounded for AC. Some color ones also have, for color difference.
This variable g1 not results in a variable beam size/spot size for these sets? Or signal is too low to produce an appreciable difference?

This subject of this thread makes me wonder about it.
(The TV here have only k driven, so will not have this issue).

I have a gut feeling that the variation in spot size with G1 to cathode voltage (that is, with beam current) outweighs the variation due to G1-G2 voltage change, but it would be interesting to know.

So I went ahead and did this. It looks a little sharper to be sure, but I found a couple more issues while I was messing around with bringing the brightness and color back to normal.

First weird thing is the AGC. That's the only internal video level control I get, so I went to set it up and the voltage is way off what the Sams says it should be. Sams wants 2.5V-2.7V at the emitter of Q207, the 1st Video Amp. I see between 600mV-1.6V maximum as I twiddle it.

As the voltage at the emitter goes down, the video signal gets stronger, which I didn't expect, but I'm just learning here I guess.

I wish I had the actual SM, but this is the best I can do otherwise. Is there any reason the voltage there would be off by what seems about double?

I checked and set the B+ when I did a recap of the set.


EDIT: OK I found the SM. It looks like Sams is wrong. It's supposed to be 2.6V at the BASE not the EMITTER, and readings are with a colors bars pattern displayed or nothing. Sams didn't mention any of those details.


https://i.imgur.com/uL5S3Am.png

Having some time to actually view material on it and not just stare at test patterns, I can definitely say that it's a bit sharper than it was. Putting the G1 to ground seems to have helped, and there's plenty of headroom for brightness past where it's currently set. Also checking the AGC and afterwards redoing the white balance and screen settings has made an enormous improvement in the over color reproduction.

I am still seeing a slightly diminished bright red and blue bar, but it's nowhere near as bad as it was before.

I wonder if it isn't also necessary to redo the IF sections because I've never touched them. I haven't done TV IF adjustment before and I'm not sure exactly what to do.

I want to also note that the image jumps around a bit while it's running. It doesn't do it constantly, but every so often it will bounce in and out of vertical hold seemingly.

I wonder if there's any way to make the image more stable?

Tap on things and wiggle connections to see if some particular thing is sensitive to vibration.

Over time with using it with the G1 at 0V the wiggliness has almost disappeared, so I'm not terribly worried about it anymore.

I have noticed with this set that the image seems to get a little brighter on the right side of the screen, so I decided to investigate the power supply for the RGB output transistors. I noticed that the 162VDC supply was coming in a little bit low, and with a little bit more of an AC component than I expected to see. I also scoped the derived 130VDC supply and found that it was around 125V

The OG diode was a HF-1Z with an epoxy blob on the back, so I swapped it for a 1N4937 and now the voltages are closer to what they should be. I see the 130V at around 128-129, and the 162 is about 160. The AC component is halved.

This got me thinking if maybe there was something I could do to improve the performance of the output transistors on the neck board.

I wonder if swapping the 2SC1127 transistors out for something more modern, or with higher gain would improve things at all, especially since pegging the G1 to zero volts required that I raise the G2 to compensate a bit?

I know it's got to at least be able to handle the conditions of the original component, but I'm wondering which characteristics I need to pay most attention to in order to tune the circuit in a beneficial way?

The 2SC1127 has an hFE of 1000, so would I be looking for something that was just a bit higher or something?

https://i.imgur.com/vFIEKs1.png

Also was looking again at the focus voltage now that I've done the G1 mod and I realized that it's actually having an effect to use a potentiometer on the focus. Only issue is that it's loading down the G2 voltage and making me turn up the G2 close to it's limit. I think I can prevent this with another resistor or something, but I'm not sure how big it would need to be.

As far as the Focus Voltage project goes, I am still trying to work out how best to set it up in order to prevent loading the G2.

I have the 1 megaohm potentiometer that purchased for this project, along with some various power resistors, the largest of which is 27k 2W. I can always buy another couple of resistors, but I'd like to do it with what I have on hand.

The original Focus circuit has a 470k 1/2W resistor in series with the Focus Grid. I'm not entirely sure if it's capable of handling a modified circuit that includes a resistive divider to pull down the focus voltage, but this is what I'm currently thinking about:

https://i.imgur.com/C6Bis6s.png

I also have some 1.6kV 1.5A diodes I could maybe use to isolate the G2 from the Focus voltage circuit, maybe preventing the load down?

Any opinions or advice on this?

TIA

Without looking back......
SAMS & most other SM's show wave forms & voltages with a clean signal & given pattern, it is noted in the docs. AGC can vary WIDELY from no sig / full signal.

L-R shading for me has ALMOST ALWAYS been the filter cap for the @200 V
supply. Its across all brands ! Thats hundreds of sets. Just blanking & video coupling caps were found a few times. IIRC there is one in you Sony.

As far as TNR / IF alignment go DONT DO IT ! When 17 yrs old my first TV
repair job I was told NEVER F with it or I will get fired ! He meant it. FAFO.
Yes there are a few traps you can do by eye but thats rarely needed.

time for a brew:beer:
Zeno
LFOD !

Without looking back......
SAMS & most other SM's show wave forms & voltages with a clean signal & given pattern, it is noted in the docs. AGC can vary WIDELY from no sig / full signal.

L-R shading for me has ALMOST ALWAYS been the filter cap for the @200 V
supply. Its across all brands ! Thats hundreds of sets. Just blanking & video coupling caps were found a few times. IIRC there is one in you Sony.

As far as TNR / IF alignment go DONT DO IT ! When 17 yrs old my first TV
repair job I was told NEVER F with it or I will get fired ! He meant it. FAFO.
Yes there are a few traps you can do by eye but thats rarely needed.

time for a brew:beer:
Zeno
LFOD !

Thanks Zeno.

I did observe the color bar requirement in the Sams when setting AGC. I didn't mess with the IF! I would not as I don't have the right equipment to do up right anyways and I'm not so bold.

L-R shading for me has ALMOST ALWAYS been the filter cap for the @200 V
supply.

Yes, there's a lytic cap there it's been replaced with the same value. C524, 4.7uf, 50V. I could swap it out for something higher I guess? Like maybe a 10uf.

Any ideas about controlling the focus voltage without loading down the G2? I thought maybe if I put a diode between the 530V and the 1M pot it could prevent that, but not sure if it's the right approach.

C524 voltage rating should be much higher than 50 volts. Try a 5 or 10 meg focus control so as to not load down the supply voltage.

C524 voltage rating should be much higher than 50 volts.

I thought it did seem kind of weird while I was looking at the schematic today, so I used a 250V 10uf cap to see if I got any improvement in the evenness of the brightness, but I did not.

However, Sony used a 50V part there. That's what I pulled out of it (it was dead, but it said 4.7uf 50V), and that's what the schematic says it should be.

https://i.imgur.com/3hidZ3a.png





Try a 5 or 10 meg focus control so as to not load down the supply voltage.

I don't currently have one that big. I have 1.6kV diodes though! Would it make sense to throw a diode between the 530V and the 1M potentiometer to prevent load? Like this:

https://i.imgur.com/Z6Gb0Gk.png

The diode only will serve to make a voltage offset; will not isolate anything (unless the focus grid supply current...). Is better to invest in the resistor values.

C524 is probably stacked on the B+ instead of going to GND like
most sets so 50 V rating used. Fisher & GE also did this. Most
others used a 4.7 or 10mfd 315 V to GND.
Zeno

The diode only will serve to make a voltage offset; will not isolate anything (unless the focus grid supply current...). Is better to invest in the resistor values.


Okay, I thought the current loading was the issue, but I guess you're saying that it's actually a voltage drop on the screen?

The issue I'm having with this is that when I put the 1M pot in the circuit with the other side to ground, it creates a load on the screen supply and the screen dims. I thought it was a current issue, but I guess it would make sense that it's creating an additional resistive divider for the screen potentiometer. There is a lot going on in this circuit, and I'm having trouble visualizing exactly what happens when I put the pot in. It's like this, and the arrow is where I would put the proposed diode in place:

https://i.imgur.com/iyBW4v7.png

Otherwise, are you saying that I can prevent the voltage drop by using a higher value resistor to supply the Focus Grid, with another one to ground on the other side? I think I mainly need help understanding exactly why the G2 is becoming dim in order to fix it because I don't know how to do the calculations for the resistors if that is so.

C524 is probably stacked on the B+ instead of going to GND like
most sets so 50 V rating used. Fisher & GE also did this. Most
others used a 4.7 or 10mfd 315 V to GND.
Zeno

Yes, it's stacked on the B+. There's a .01uf film or ceramic (I'm not inside right now) going to ground between B+ and 162V Source. I guess I could try replacing that instead, or increasing it a bit if it looks okay. I've seen some film caps go bad I guess, but it's very rare.

Okay, I thought the current loading was the issue, but I guess you're saying that it's actually a voltage drop on the screen?

The issue I'm having with this is that when I put the 1M pot in the circuit with the other side to ground, it creates a load on the screen supply and the screen dims. I thought it was a current issue, but I guess it would make sense that it's creating an additional resistive divider for the screen potentiometer. There is a lot going on in this circuit, and I'm having trouble visualizing exactly what happens when I put the pot in. It's like this, and the arrow is where I would put the proposed diode in place:

https://i.imgur.com/iyBW4v7.png

Otherwise, are you saying that I can prevent the voltage drop by using a higher value resistor to supply the Focus Grid, with another one to ground on the other side? I think I mainly need help understanding exactly why the G2 is becoming dim in order to fix it because I don't know how to do the calculations for the resistors if that is so.

If focus adjustment are great at near top, you can add a some Mohms resistor from "cold" wiper from potentiometer to ground (in series with potentiometer), reducing the loading, and making the focus adjusment less coarse.

If focus adjustment are great at near top, you can add a some Mohms resistor from "cold" wiper from potentiometer to ground (in series with potentiometer), reducing the loading, and making the focus adjusment less coarse.


The actual voltage at the 530V boost line measures at about 560VDC at the source. The focus looks best at something like 400VDC.

Good, so is possible to add the resistor.
BTW: I wrote "in the wiper" (perhaps making some confusion), so I can explain better: the resistor needs to be added in series with the ground side of it; the pot. pin dedicated to low voltage, and potentiometer being only a part of the divider. Like a 3M3 resistor in the ground side, then to the one leg of pot. The movable part of it goes to focus grid, and remaining part of the potentiometer simply goes to 530V. Total, more than 4M, better than the only 1M from potmeter.