Carbon composite in place of carbon film

[DaveWM]

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

[TinCanAlley]

Originally Posted by DaveWM

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.

[DaveWM]

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.

[TinCanAlley]

Originally Posted by DaveWM

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.

[TinCanAlley]

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.

[DaveWM]

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.

[TinCanAlley]

Originally Posted by DaveWM

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!

[TinCanAlley]

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.

[DaveWM]

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.

[TinCanAlley]

Originally Posted by DaveWM

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.

[TinCanAlley]

Originally Posted by DaveWM

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).

[DaveWM]

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.

[TinCanAlley]

Originally Posted by DaveWM

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.

[DaveWM]

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)

[TinCanAlley]

Originally Posted by DaveWM

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.