Carbon composite in place of carbon film - Videokarma.org TV - Video

DaveWM · #1 08-23-2013, 12:56 PM

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.

TinCanAlley · #2 08-23-2013, 01:02 PM

Quote:

Originally Posted by DaveWM

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

DaveWM · #3 08-23-2013, 01:03 PM

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

TinCanAlley · #4 08-23-2013, 01:06 PM

Quote:

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 · #5 08-23-2013, 01:12 PM

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 · #6 08-23-2013, 02:47 PM

Quote:

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 · #7 08-23-2013, 03:11 PM

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.