As many of you know, I'm trying to fix jail bars on my Zenith Avanti (yes, still). With the help of a few here, I'm about to replace the resistors, diode and transistor in the blanking circuit. I managed to get an NOS Zenith diode and transistor, but the resistors weren't available. I ordered the replacements from Mouser and they arrived on Saturday. When I went through them, I noticed for the 100K 1/4w 5% carbon film I ordered the 100K 1/4w 5% Carbon Composite. I was ordering the 33K and 82 composites and I must have zoned out and kept in that section when ordering the 100Ks.

Anyway, I've searched and read lots on the internet and found the composites are not as stable as film. Now, granted, most sites were in regards to music amps and such, and talked about noise as well. So what I need to know is if I should use them or run out to Radio Shack and get the metal. Only issue with RS is they don't list a manufacturer, so I don't know the quality.

Anyway, thanks for any input.

Since you have them handy I'd use 'em. While true that carbon comp's can drift, become noisey, etc. you do have some new ones at your disposal. Not all carbon comp's go bad "just because" and I'm sure there are still lots out there operating just fine including my sets and equipment too.

Since you have them handy I'd use 'em. While true that carbon comp's can drift, become noisey, etc. you do have some new ones at your disposal. Not all carbon comp's go bad "just because" and I'm sure there are still lots out there operating just fine including my sets and equipment too.

Cool. Just wasn't sure if they would be a fit in that circuit. I know they're all over the bottom of the chassis, but there's also lots of carbon films as well. Can't figure out the logic behind using two different types unless the characteristics of each type fit the intended use.

Thanks for the input.

good luck with it I hope it fixes the problem. Try the transistor 1st as its just a plug in IIRC.

oh and if it was me I would prob just j hook in those parts to avoid stress on other stuff. I am pretty sure the diode is silicon but I would put a heat sink on it any way.

Do yourself a favor, check the NOS parts before installing thats the diode and transistor.

good luck with it I hope it fixes the problem. Try the transistor 1st as its just a plug in IIRC.

You read my mind. I have the transistor in front of me and am about to test it. If it tests okay, it goes in and I fire her up. If that doesn't help, I flip her over and start the resistors and diodes.

:thmbsp::yes:

BtW, does your schematic give you voltage readings for that transistor? if so it would not hurt to check them. Make sure you check the notes regarding without signal, line voltage etc...

Be VERY careful reading voltage with SS parts, a slip of a prob can instantly destroy a diode or transistor.

:thmbsp::yes:

BtW, does your schematic give you voltage readings for that transistor? if so it would not hurt to check them. Make sure you check the notes regarding without signal, line voltage etc...

Be VERY careful reading voltage with SS parts, a slip of a prob can instantly destroy a diode or transistor.

Yep, it has the voltages. Is it better to probe the bottom lead of the socket, or try to read directly from the exposed part of the legs of the transistor itself?

I realize I put this thread in the wrong forum. How do I move it?

:thmbsp::yes:

BtW, does your schematic give you voltage readings for that transistor? if so it would not hurt to check them. Make sure you check the notes regarding without signal, line voltage etc...

Be VERY careful reading voltage with SS parts, a slip of a prob can instantly destroy a diode or transistor.

Well I replaced the transistor and it didn't help. Figured since I was in there I change the other since I had the replacements. I managed to change all of them except for the 3rd Video Amp. When I installed it, there was no picture. I reinstalled the original and it worked fine. The legs on the replacement are not in a row (they in an arc). I know the center back is the base and I had assumed that since the outer two were forward of the base, it would install in the socket that way. Am I wrong? Do I need to bend the legs backwards to rotate and install it?

the sams should id the pins of the existing trans or you can look a the schematic to figure it out. then you need to look at the replacement and check the package for what pins are what.

Yep, it has the voltages. Is it better to probe the bottom lead of the socket, or try to read directly from the exposed part of the legs of the transistor itself?
I find it best to go from top of chassis, get some test prob clips from rat shack, they fit over the tips of reg test probs and have little j hooks that extend and retract, hook up everything with the set off and make sure there are no shorts and that the DMM is in the correct setting, then power up. take readings, power off and remove the clips.

BTW no need to replace anything but the Blanking transistor the others would not account for the jail bars (at least should not).

Don't make too many changes or substitutes. You want to try and diagnose the problem and not shot gun parts at it. If the diode/ blanking transistor/cap/resistors to not resolve it then you are into tough dog territory, and you need someone that has a scope and some real talent to fix it.

I only hope that the target parts are it, again its really just an educated guess.

I find it best to go from top of chassis, get some test prob clips from rat shack, they fit over the tips of reg test probs and have little j hooks that extend and retract, hook up everything with the set off and make sure there are no shorts and that the DMM is in the correct setting, then power up. take readings, power off and remove the clips.

BTW no need to replace anything but the Blanking transistor the others would not account for the jail bars (at least should not).

Don't make too many changes or substitutes. You want to try and diagnose the problem and not shot gun parts at it. If the diode/ blanking transistor/cap/resistors to not resolve it then you are into tough dog territory, and you need someone that has a scope and some real talent to fix it.

I only hope that the target parts are it, again its really just an educated guess.

I have those little suckers with the hooks.

I'm going to do the testing.

Okay, after a total brain fart and leaving the positive lead in the OHM connection, I finally have the numbers.

For the blanking transistor I got 6.8V for the Emitter (SM has 7.19V), Base was 3.9V (SM has 4.43V) and the Collector as 23.4V (SM has 23.5V).

those all look pretty good, You can still try the diode (I would just unsolder and check the a DMM compare to the new one) then the resistors. This may be very late question, but do you have the brightness cranked up? or the contrast real low?

those all look pretty good, You can still try the diode (I would just unsolder and check the a DMM compare to the new one) then the resistors. This may be very late question, but do you have the brightness cranked up? or the contrast real low?

Funny you should ask. I have the contrast at a comfortable level and there's plenty of travel left on the control. You only need to turn less than a 1/4 to get the right level.

The brightness, on the other hand, is almost full. There's not headroom in the control. The full rotation gets you just over where it should be. I back it down just a bit to get to the right level. I could have sworn it had much more range before I started my repair work.

Why are you asking? Is there something in the numbers?

Also, if the numbers look okay, does that mean the resistors are probably okay as well? I will do the diode on Wed. I'm running out of steam and don't feel like flipping her over at the moment.

well if it checks out (the blanking) then I was thinking something may be a miss in the overall bias of the CRT.

You should get that working (brightness control).


Check all the voltages on the CRT (G1 G2 and Cathodes).

well if it checks out (the blanking) then I was thinking something may be a miss in the overall bias of the CRT.

You should get that working (brightness control).


Check all the voltages on the CRT (G1 G2 and Cathodes).

The CRT checks out okay on the B&K tester and the G2 voltages were good as well. Could it be possible I didn't set the G2s high enough when I did the grayscale adjustment? I disconnected the IF, turned all G2s down and then turned red up until dim raster and backed off until it disappeared ( don't like the setup line). I did the same for the blue and Green. I didn't see a need to move the taps, so they're on medium.

well how do the voltage look at the G2? based on your setup, warning they will be pretty high so make sure your meter can handle it.

If the brightness control is turned way high, and its part of the same circuit that has the blanking maybe there could be a problem..

well how do the voltage look at the G2? based on your setup, warning they will be pretty high so make sure your meter can handle it.

If the brightness control is turned way high, and its part of the same circuit that has the blanking maybe there could be a problem..

Each G2 measured around 752 with pot turned up and around 420 with it turned down.

where was it when you did your setup?

where was it when you did your setup?

When did what setup? If you mean the grayscale, they were all the way CCW which would make them about 420V. I don't know what they ended up at as I didn't think to measure.

when you did the orig CRT setup you said something about not liking to use the setup switch bur rather seting up the red raster then the other colors.

Now you have the set working but you say the brightness control must be set to max.

I presume the jail bars are happening with this setup.

So

now measure the crt pin voltages. don't move the pots I just want to know what the voltage are after you did the setup and had the picture that you say is low in brighness.

when you did the orig CRT setup you said something about not liking to use the setup switch bur rather seting up the red raster then the other colors.

Now you have the set working but you say the brightness control must be set to max.

I presume the jail bars are happening with this setup.

So

now measure the crt pin voltages. don't move the pots I just want to know what the voltage are after you did the setup and had the picture that you say is low in brighness.

Oh, I get it. That setup was the grayscale. The setup switch puts a single horizontal line across the screen and you're supposed to turn up the G2s so you get a white line. It's to hard to do this, so I used another's suggestion about pulling the IF cable and going with a full screen raster. The only difference is, and this could be the issue, is that with the IF disconnect way, you turn up till visible and then down til just off. With the setup line, you want each visible. So maybe turning back til just off is making it too dim for good brightness.

Oh, and I'm not maxed out, but just about. There's about 1/8" movement left in the control. I know on my other CCII, there's about 3/16 or more left and can get pretty bright.

When I flip her over Wednesday, I'll measure the G2 voltages as set.

That seem odd, with a good CRT and the G2's turned up 7/8 the pic should be way bright. Something is not right. The thing with CRTs is if you the correct HV and the votages are right and the CRT has good emissons it pretty much has to work right (brighness).

should be interesting to get the readings. something is off on the bias maybe in the cathode circuit after all (back to the video amp).

if all the cathodes are too high it would cutoff the CRT, the driver transistors get there signal for the luma from the emitter circuit, the base is the chorma.

for grins check the emitter voltages of those 3 power transistors (should all be the same about 16v no signal)again be careful on slip and you will ruin the transistors.

That seem odd, with a good CRT and the G2's turned up 7/8 the pic should be way bright. Something is not right. The thing with CRTs is if you the correct HV and the votages are right and the CRT has good emissons it pretty much has to work right (brighness).

should be interesting to get the readings. something is off on the bias maybe in the cathode circuit after all (back to the video amp).

if all the cathodes are too high it would cutoff the CRT, the driver transistors get there signal for the luma from the emitter circuit, the base is the chorma.

for grins check the emitter voltages of those 3 power transistors (should all be the same about 16v no signal)again be careful on slip and you will ruin the transistors.

Okay, the G2s are: Red=488V Green=453V Blue=456V

How are those numbers? And it's not the G2s that are turned up that far, it's the brightness control on the front of the set that up.

those all look pretty good, You can still try the diode (I would just unsolder and check the a DMM compare to the new one) then the resistors. This may be very late question, but do you have the brightness cranked up? or the contrast real low?

Okay, unsoldered the leg of the diode. It measured 584 or so one way, infinity the other. So I'm assuming it's good, right? That's really the only test you can do on a diode, right?

what does the sams say the G2s should be? that seems low to me.

before doing anymore work on the jail bars you need to get the brightness thing worked out.

do the setup per the sams, (with the service switch) then check the brightness control and the G2 voltages.

and yes the diode is fine.

what does the sams say the G2s should be? that seems low to me.

before doing anymore work on the jail bars you need to get the brightness thing worked out.

do the setup per the sams, (with the service switch) then check the brightness control and the G2 voltages.

and yes the diode is fine.

Okay, the SM shows: Red=590 Green=640 and Blue=540

So I need to bring the G2s up to roughly those values? I know they go that high and higher from testing, but didn't know I was aiming for those values when adjusting.

I'll have to do it tomorrow. Got a busy day today.

its not that you are aiming for those that is just what sams got, my concern is if you deviated from the correct G2 setup procedure, then the bias of the tube may be off, making other things (maybe the jail bars) become an issue.

just do the setup as defined in sams, check the voltages and post back the results if brightness is still an issue then need to look at the other voltages and try to figure out why, brightness should not be an issue with a good tube with correct HV and pin voltages.

its not that you are aiming for those that is just what sams got, my concern is if you deviated from the correct G2 setup procedure, then the bias of the tube may be off, making other things (maybe the jail bars) become an issue.

just do the setup as defined in sams, check the voltages and post back the results if brightness is still an issue then need to look at the other voltages and try to figure out why, brightness should not be an issue with a good tube with correct HV and pin voltages.

I'll readjust them first thing on Wednesday per SM instructions.

its not that you are aiming for those that is just what sams got, my concern is if you deviated from the correct G2 setup procedure, then the bias of the tube may be off, making other things (maybe the jail bars) become an issue.

just do the setup as defined in sams, check the voltages and post back the results if brightness is still an issue then need to look at the other voltages and try to figure out why, brightness should not be an issue with a good tube with correct HV and pin voltages.

Okay, I could not go the setup switch approach. The only G2 that put a line on the screen was the blue. The red and green wouldn't show. So I brought up a grayscale pattern and adjusted it that way. After doing that and adjusting the taps, the red voltage was 590V, blue was 550V and Green was 540V. The SM has the Green at 640V, Blue at 540V and Red at 590V. So other than the Green, the other two are pretty close.

Now I do have more brightness range, so that is good. As for the jail bars, they're still there. I changed the diode since I had to unsolder the existing to test. I didn't bother with the 100K resistors as I have the scope now and figured I'd try that before more part replacement.

you need to check the other voltage at the pins of the CRT the cathodes/G1 and G2.

It does not follow that you can not get the setup to work with the switch. If the crt test good it should work, if it does not work there is a problem.

...

you need to check the other voltage at the pins of the CRT the cathodes/G1 and G2.

It does not follow that you can not get the setup to work with the switch. If the crt test good it should work, if it does not work there is a problem.

Okay, here's where I get lost. Finding the G2 lines was easy. I just connected to them at the pots. As for the G1 lines, I don't know which ones they are. The G2s are all white with red, blue and green stripes. Then I have yellow wires with red, green and blue stripes and solid color red, green and blue wires. That makes three sets of wires and no indication in the SM as to which sets are which. I do know the black is focus, though.

I would be looking at the G2 supply. The fact that you can't get a setup line indicates that there is a problem. You should be able to easily get a setup line on all 3 guns. Ignore the exact voltages in the service manual as they will vary from one CRT to another. What is the maximum G2 voltage you can get? It should generally be around 700-900v with the controls at maximum.

I wasn't able to get a setup line on my CTC40, and it turned out to be a bad HV diode in the circuit that supplies the G2. In my case, it also caused the focus range to be off.

During testing, the range for each G2 control was roughly 450 to 729. The reading was taken directly from the output tap on the G2 pot.

the best way is to simply pull the crt socket back just enough to expose the pins, then using the rat shack spring loaded prob you clip on to one pin at a time (neg to chassis) and get a reading. you want the socket to be on enough to still work the CRT. As far as what pin is what, you should look up the CRT (google) and it will be listed along with pin out. stay away from the focus pin it will be the one that has space between it and the other pins on both sides.

dont try and just use the prob directly to the expose pin, it can be done but you risk slipping and shorting out on pin to another. far better to get it all hooked up and make sure nothing is shorted then power up, get a reading, power down and move to the next pin.

oh one last thing, if you do this a lot you use a socket adapter that goes between the CRT pins and the socket, it has test point that are clearly labeled that make checking pin voltage easy.

the best way is to simply pull the crt socket back just enough to expose the pins, then using the rat shack spring loaded prob you clip on to one pin at a time (neg to chassis) and get a reading. you want the socket to be on enough to still work the CRT. As far as what pin is what, you should look up the CRT (google) and it will be listed along with pin out. stay away from the focus pin it will be the one that has space between it and the other pins on both sides.

dont try and just use the prob directly to the expose pin, it can be done but you risk slipping and shorting out on pin to another. far better to get it all hooked up and make sure nothing is shorted then power up, get a reading, power down and move to the next pin.

oh one last thing, if you do this a lot you use a socket adapter that goes between the CRT pins and the socket, it has test point that are clearly labeled that make checking pin voltage easy.

Well I used the hook probe and got all the voltages. The only ones I know for sure are the G2 leads. I'm assuming the G1s are the yellow wires since their voltages are around 140V which I believe is the cutoff voltage? I was unable to find anything on the internet searching for my CRT model and pinout.

I'll put the values in the SM first and then actual.

SM Values Actual Values

2 = 143 153
6 = 142 144
11 = 142 147

3 = 36.4 33.4
7 = 36.4 33.4
12 = 36.4 33.4

4 = 590 600
5 = 640 548
13 = 540 540

All the numbers seem good and within range.

Pin

hmm, well thats odd that you can't get the setup to work then.

my service manual shows 180v at the collectors of output transistors when in the service mode. check that. again extreme care with the probes or you can smoke a SS device is a fraction of a second.

you need to check the other voltage at the pins of the CRT the cathodes/G1 and G2.

It does not follow that you can not get the setup to work with the switch. If the crt test good it should work, if it does not work there is a problem.

Kind of late, but my skills at reading the schematics must be getting better. I just found that there are test points for the G1s at the chroma gain taps. Seems T, S and R are the G1s and you can measure the voltage from there. I just did that and got the same voltages there as the pins (well within a volt). :banana:

good now check them in the service mode. I think it should be close to the 180v

hmm, well thats odd that you can't get the setup to work then.

my service manual shows 180v at the collectors of output transistors when in the service mode. check that. again extreme care with the probes or you can smoke a SS device is a fraction of a second.

Will have to flip her over for this one. The output transistors are TO39 casings and the legs were cut so they sit flush to the socket. I'll have to do it from the bottom.

Oh, never mind. Seems the test points I found are the collectors you mentioned. No need to flip her. :thmbsp:

I am a little behind you, try checking at those same point you found, should be close as I think there is only a 1k resistor between them and I doubt there would be a lot of voltage drop.

I am a little behind you, try checking at those same point you found, should be close as I think there is only a 1k resistor between them and I doubt there would be a lot of voltage drop.

Okay, here's what I got from the output collectors at the test points in setup:

Red = 197V
Blue = 184V
Green = 192V

which line did you say you could get in the setup mode?

which line did you say you could get in the setup mode?

Both red and blue wouldn't come up. Green did, but it was very weak and only came on at maximum rotation.

well those all look a bit high considering the G1 in the mid 30's give you a bias of about 160ish neg which is prob cutting of the CRT.
you would want it bias off more than normal since you want to reduce the beam current when the vert sweep is disabled but not completely cut off. Sorry I just know know what the exact number should be.



I would check the voltage of the output transistors next, and if you can get a good bright raster in reg but the serv mode does not work, then I would check the resistors and that ties the emitters of the outputs back to ground AND that blanking signal from the fly. Now would be a good time to trace the flyback signal with the scope.

It looks like the emitters get voltage from the emittier of the video driver in reg mode, but in the service mode they are grounded thru a 1.5k and a 12k that gets the flyback pulse. look this over carefully on the schematic until you see what I mean.

well those all look a bit high considering the G1 in the mid 30's give you a bias of about 160ish neg which is prob cutting of the CRT.
you would want it bias off more than normal since you want to reduce the beam current when the vert sweep is disabled but not completely cut off. Sorry I just know know what the exact number should be.



I would check the voltage of the output transistors next, and if you can get a good bright raster in reg but the serv mode does not work, then I would check the resistors and that ties the emitters of the outputs back to ground AND that blanking signal from the fly. Now would be a good time to trace the flyback signal with the scope.

It looks like the emitters get voltage from the emittier of the video driver in reg mode, but in the service mode they are grounded thru a 1.5k and a 12k that gets the flyback pulse. look this over carefully on the schematic until you see what I mean.

Okay, I got the voltages of each base of each output transistor (both in and out of setup).

The first value is SM, second is normal and the third is in setup mode.

Red: 15.6, 15.9 and 16.6
Green: 15.6, 16.1 and 16.7
Blue: 15.7, 16.2 and 16.8

I see on the schematic the setup/normal. In setup I see a 1.8K and a 18K (not the 1.5K and 12K you noted). After that, I see it tie in somewhere in the vert/horz blanking and then it goes to pin 4 of J201 and also is connected to green of T207. I'm lost after that. I can see how switching to setup takes the voltage away from the emitters fed by the video amps. T207 is the horizontal output transformer, so I guess that's the source of power for the emitters in setup. J201 pin 4 goes to the convergence board and I don't see how that fits in.

Guess I'm not getting that much better navigating schematics. If you could give me a clue as to where the flyback signal for probing is to be found, that would be great. I don't know where along the circuit to probe. Is it the H Sweep of the horizontal module, or the base of the horizontal output transistor? Or...is it in a completely different location?

Sorry to be such a pain. I hope I'm not coming along too slowly.

Just noticed something...might be nothing...might be something....

As you know I haven't been able to converge the blue lines very well and in some areas they are way off on the left and right of the screen. Well in tracing this current circuit, I noted that the blue convergence lines right and left are coming off of pin 4 of J201. That's the one fed by the by the setup we've been tracing. Even when in normal, there is the signal coming from the vert/horz amps tied in with the two 100K, 33K and diode we've been eyeing.

Now it might not be connected, but I thought I'd toss it out here.

you read the base voltage, look for the emitter voltage this would be normal mode no signal (raster).

Yes I noted the connection to the convergence board, and no I do not know if that is related.

1st things 1st get that emitter voltage my guess is changing from normal to setup alters those voltages as a means to bias the transistor to cut off more when in setup mode.

as far as scoping I would start by seeing if the sam wave form matches, if it does then thats a dead end, if not then you would just start working back towards the flyback. That horz pulse at the convergence board will will prob look a lot like the one you see in my video which is also a flyback pulse for convergence. PP may be different but I suspect the shape will be about the same.

you read the base voltage, look for the emitter voltage this would be normal mode no signal (raster).

Yes I noted the connection to the convergence board, and no I do not know if that is related.

1st things 1st get that emitter voltage my guess is changing from normal to setup alters those voltages as a means to bias the transistor to cut off more when in setup mode.

as far as scoping I would start by seeing if the sam wave form matches, if it does then thats a dead end, if not then you would just start working back towards the flyback. That horz pulse at the convergence board will will prob look a lot like the one you see in my video which is also a flyback pulse for convergence. PP may be different but I suspect the shape will be about the same.

Okay, the emitters could only be measured at a point on the other side of the 180ohm resistor (unless I flip her over and removed the stand and cover). Measuring though the 180ohm resistor gave me 14.3V normal and 15.5 setup. Is going through the resistor okay, or do I need to go directly to the emitter lead?

I feel really stupid, but I can't get the scope to do what I want. I connected it to the S test point though a 10x probe in 1x mode and couldn't figure out how to adjust the darn controls to give me a usable waveform. If you look at the pic I posted in the thread asking if the scope was okay, could you step me though setting the main controls for it? The manual it came with is basically useless, at least it is for me. I'm sure if I can be pointed in the right direction for setup, I'll be able to adjust from there for other points.

Thanks!

Okay, this is the waveform I got off the convergence board's white/green wire. In the first pic is how Sams shows the waveform (it's the one on the right). In the second pic is what I managed to get on the scope. I know I must be missing something as I got two waveforms and couldn't merge them or make them bigger.

hard to say about the scope you should be able to increase the size with the vert amp and stretch it out with the sweep rate.

Don't know what to tell you bout testing the emitters. I would test the way the sams says to. We are trying to figure out why the setup does not work. Until you get that working I would hesitate to work on anything else.

I think the bias voltage are off, so i would concentrate on those transistor voltages.

hard to say about the scope you should be able to increase the size with the vert amp and stretch it out with the sweep rate.

Don't know what to tell you bout testing the emitters. I would test the way the sams says to. We are trying to figure out why the setup does not work. Until you get that working I would hesitate to work on anything else.

I think the bias voltage are off, so i would concentrate on those transistor voltages.

Okay, I'll flip her over and open her up to test the emitters directly from the socket and not through the attach resistor. Also, if I were to pull the transistor, wouldn't this also allow me to test the resistor? It would be the same as cutting one let as without the transistor in the socket, there's nothing connected to the leg.

I think there's an issue with the scope. If I put the probe in the vertical input, I get a nice tall waveform. Only issue is, I need the horizontal input for what we're checking. Also, I noticed that when measuring the horizontal, the waveform distorts when I put my hand near the vertical input or sync amplitude knob. This poor scope has seen better days, I guess. I think it's over 50 years old.

hard to say about the scope you should be able to increase the size with the vert amp and stretch it out with the sweep rate.

Don't know what to tell you bout testing the emitters. I would test the way the sams says to. We are trying to figure out why the setup does not work. Until you get that working I would hesitate to work on anything else.

I think the bias voltage are off, so i would concentrate on those transistor voltages.

Okay, I did the emitters and all of them had a normal of 15.7V and a setup of 16.2V. each of the 180ohm resistors on them were within tolerance (about 176ohms each).

I checked my manual the white green should be 22v pp close enough to sams 20v.

you need to calibrate the scope use a 9v battery if there is no calibration point on the scope (more modern ones have a 5v pp square wave generator to test to). put a 9v battery and note how far a trace deflects, adj the vert amp to get a size that is easy to work with and will nearly fill out the screen on the scope if it was 22v (so make the 9v move the line little less than 1/2 the screen that way a 20v spike will nearly fill it. There are markings on the screen if you try to use those to represent 1v each.

increasing the sweep rate should let you see fewer spikes. I dont know much about scopes only the one I have, so not sure how keying works on yours.

I checked my manual the white green should be 22v pp close enough to sams 20v.

you need to calibrate the scope use a 9v battery if there is no calibration point on the scope (more modern ones have a 5v pp square wave generator to test to). put a 9v battery and note how far a trace deflects, adj the vert amp to get a size that is easy to work with and will nearly fill out the screen on the scope if it was 22v (so make the 9v move the line little less than 1/2 the screen that way a 20v spike will nearly fill it. There are markings on the screen if you try to use those to represent 1v each.

increasing the sweep rate should let you see fewer spikes. I dont know much about scopes only the one I have, so not sure how keying works on yours.

This might be a stupid question, but should the probe be plugged into the vertical input or the horizontal? I am unable to get a decent size display with the horizontal input, but with the vertical input I can expand to fill the screen. Only issue is, I believe I need the horizontal input because we're aiming to check the horizontal circuit, right? If that's the case, I think this old thing is in need of repair.

Now on to the setup issue. I decided to check the red G1, G2 and screen voltage both in and out of setup from the pins on the CRT. I figured that if the line wouldn't come up at all for the red, it was the best to check. Here's what I got.

The first number is in normal mode and second is in setup mode:

G1 = 161, 192
G2 = 605, 612
Scr = 33.6, 34.3

Now the G1 is supposed to be 140V and the G2 should be around 590V. The Screen voltage is supposed to be around 36.4. Except for the G1, all numbers are pretty close. I don't know how much voltage difference is allowed for G1, but if I understand things correctly, it's voltage varies in conjunction with the G2.

cathodes are 6 2 11 180v in setupmode
g1 are 12 3 7 40v
g2 are 13 4 5 I dont have it but think sams is around 600v

terminology is

Cathode
G1 is the control grid
G2 is the Screen grid
G3 (listed that way on data sheet) is the focus pin)

in some sets the luma is from cathodes and the chroma is from the control grid, the mixing of the Y and B-Y/G-Y/R-Y takes place in the CRT on this set its done at the video out transistors (base for chroma, emitter for luma)

I checked my manual the white green should be 22v pp close enough to sams 20v.

you need to calibrate the scope use a 9v battery if there is no calibration point on the scope (more modern ones have a 5v pp square wave generator to test to). put a 9v battery and note how far a trace deflects, adj the vert amp to get a size that is easy to work with and will nearly fill out the screen on the scope if it was 22v (so make the 9v move the line little less than 1/2 the screen that way a 20v spike will nearly fill it. There are markings on the screen if you try to use those to represent 1v each.

increasing the sweep rate should let you see fewer spikes. I dont know much about scopes only the one I have, so not sure how keying works on yours.

According to the Sams, wht/grn should be 170v. I think I got a better setup this time. I'm attaching a pic of the pattern I got. Other than the distortion of the wave (not sure if that's the signal or my settings) it looks kind of like the waveform in the SM.

Never mind the last post about the waveform. Seems it was generating that even after I disconnected the probe. I'm going to give it back to my brother and see if there is somewhere around here that rents them.

yep, with tvs you can only go so far with voltage readings, wave forms are were its at. put it back together and get some screen shots showing brigtness and the jail bars again.

Scopes are handy but expensive for a good one, you can get decent later models for around 100$ but you risk it not working, case in point my scope just took a dump on me so now I have to fix it.

You may just want to try your hand at fixing that scope, its prob pretty simple.

You do need to get a straight trace that reacts as it should.

yep, with tvs you can only go so far with voltage readings, wave forms are were its at. put it back together and get some screen shots showing brigtness and the jail bars again.

Scopes are handy but expensive for a good one, you can get decent later models for around 100$ but you risk it not working, case in point my scope just took a dump on me so now I have to fix it.

Yeah, most of the scopes I've found listed for a decent price are either broken or untested (untested=broken most of the time). I can't really justify spending a decent amount on something I might use one or twice. I have a closet full of stuff like that already.

I'm attaching a pic of the jail bars and brightness. The brightness is greatly improved with much more available range, so that seems resolved. The jail bars, however, are still there and quite noticeable (even in lighter scenes). I've replaced the two 100K resistors, the 33K and the diode. None had any effect.

I have the scope's build instructions and I can go over it. If I'm not mistaken, this thing has tubes in it. I'll take them out and test them.

This scope has 10 tubes in it! Where to begin. :scratch2:

Well my brother built it, I'll have to enlist his help.

if the scope has not been recapped it may have issues there.

the fact that the horz convergence is not responding (I think that is what you said) and the horz blanking may be causing the jail bars sure points to a problem there. Is the width ok? not too wide?

if the scope has not been recapped it may have issues there.

It's been recapped, but I don't know how long ago. I see a combination of electrolytic, film and those "orange drops" in it. I'm seeing my brother tomorrow, so I'll get more info on what's been done to it. He said it worked the last time he used it, but I didn't has how long ago that was.

the fact that the horz convergence is not responding (I think that is what you said) and the horz blanking may be causing the jail bars sure points to a problem there. Is the width ok? not too wide?

The horizontal convergence for the blue moves quite a bit, but just not in line with the other colors on the sides. There is the coil and two pots that move around the blue, but no combination of them will get the lines where they should be on the sides without messing up the top and bottom horizontal lines (center convergence stays put).

I've gotten used to no overscan, so this set's image seems too wide. I believe, though, that the overscan is about 6%. I can just see the edge of the 5% line on the overscan pattern.

I may be missing something here, but why is the scope thought to be in need of repair... the waveform posted looks reasonable, and perhaps the 10 or so "ripples" at the bottom of the waveform might indeed correspond to the 10 or so bands "jail bars" seen across the TV screen?
jr

I may be missing something here, but why is the scope thought to be in need of repair... the waveform posted looks reasonable, and perhaps the 10 or so "ripples" at the bottom of the waveform might indeed correspond to the 10 or so bands "jail bars" seen across the TV screen?
jr

If you scroll up to post #53 you'll see a waveform I posted. The waveform for the 170V in the pic is what supposed to be on the scope. I thought I had it, but that waveform didn't go away when I removed the probe. So it most likely isn't from the circuit, but from the scope itself.

I recalibrated the scope per manual and I was able to get both of those waveforms in the picture from the SM. However, all other attempts to scope out other points has given me garbage on the scope. I think there might be a short in the 10x probe.

If you scroll up to post #53 you'll see a waveform I posted. The waveform for the 170V in the pic is what supposed to be on the scope. I thought I had it, but that waveform didn't go away when I removed the probe. So it most likely isn't from the circuit, but from the scope itself.


I really suspect that the probe could have been picking up the waveform without direct connection to the test point... a sensitive probe held near the horizontal section can easily do that. If you turn the TV off, does the waveform on the scope stop?
jr

I managed to get to good waveforms from the convergence section (easiest to get to and many test points). The forms matched almost completely. Then things went wrong. I think there's a problem with the 10x probe. It's a heathkit, so I'm going to take it apart and see what might be going wrong.

if you are getting good wave form the 170v pp then trace on through and see if you can see it getting to the base of the blanker

if you are getting good wave form the 170v pp then trace on through and see if you can see it getting to the base of the blanker

I think the 10x probe is defective (it is 57 years old). I found it difficult to not only get the signal with it, but to keep it. Tapping it caused glitches. I looked over the schematics and it's pretty simple, but I don't like how the tip is designed. It's just a screw-in tip and the wire to it just hangs out the end of the probe and then the tip is attached. The wire just sit loosely in the tip, not soldered or attached in any way.

I've ordered a new probe and the BNC to banana plug converter. It should be here on Wed and I'll be able to get more done.