sylvania roundie D01

[DaveWM]

these color sets have a very simple vert integrater, no where near as many filters as my older B&W sets. Perhaps has to do with better noise rejection on the color set. still if the vert continues to be an issue I will take a look at it. the sync pulse at the vert rate did not look very nice, but it seems each color set I work on has a different looking pulse, some are very large and well defined, some not so much. Not really sure what the driving factor is, but have a feeling it may be IF alignment and perhaps some clipping.

[DaveWM]

ok check out the keying pulse, that looked good, the video signal to the control grid fo the keying tube looked ok. I really need to see the video composite signal in better detail (not the one right at the AGC tube) and look to see if the sync is getting clipped. the AGC is just WAY too critical. I still suspect its in the sync sep tube since the CRT is not getting cut off, its just the sync that gets lost at anything above just when you go from blank raster to fairly weak pic.

I tried looking at the scope signals around that noise gate transistor, but that was inconclusive, I think I will just pull that transistor out and check it.

I still need to confirm that the AGC pot is acting right, I once had a noise inverter pot that was open so it was not acting like a proper voltage divider. I think this one is ok as it seems to function normally but for the narrow range.

have had some off line discussions with another member here, and the thought is the pot may have some issues that are hard to test for with a ohm reading, but better to test by checking the DC potentials at the center lug.

[DaveWM]

doing some resistance checks of the sync amp seems to have paid off. The control grid showed no connection to anything.tracing back there is a coil that come one of the detector diodes. it was a poor solder joint, a solder blob on the pcb,with the coil wire next to it. I suppose it could have been that way from day one, perhaps over time it opened up. Lots of flux around on these boards again looks all original. Anyhow I corrected the poor solder joint, and retested the resistance, looks good now, so will reinstall the chassis later today.

I recall I was getting old looking video to the separater, but without a working set to compare its hard to tell. The sams are really not the best for showing waveforms.

I prob would have picked up on this much sooner if I had bothered to examine the PCB up close in a strong light. the poor solder joint was pretty obvious...

[holmesuser01]

I love finding things like this.

Had an RCA CTC-38 that had intermittent color. I was the 3rd person to look at it for these folks. While it was at my shop, they found a newer set they liked better, so I wound up with this set. There was a hairline crack in the foil right beside the 3.58 crystal. When I shined a high intensity light on the top side of the board, the crack in this foil stood right out. I'm the one that needs reading glasses, and I found this about 5 minutes after starting my troubleshooting.

I ran my set for almost 15 years before the OEM CRT finally gave out.

All the best to you, DaveWM!

Bruce

[DaveWM]

thanks Bruce.

Part of the problem on the visual inspection is all the old crytalized flux, I mean its EVERYWHERE. hard to see the traces thru it. I suppose it would have been easy to clean if it had been wiped off at the factory, but now its on there for good. The PCB's on this are very solid looking, they appear to be fiber glass.

[DaveWM]

that was it, AGC works as it should now, can go from pure snow to dark pic, but the sync is now there much deeper into the dark pic. Sync is rock solid vert and horz.