Today's Mystery Guest (RCA CTC-4)

[old_coot88]

I b'lieve Phil does have a 1077b Analyst.
It'd be cool if he could find a nice example of its stablemate B&K 415 Sweep Generator.
http://radiomuseum.org/r/dynascan_sw...rator_415.html
Since he's already got a nice scope, he'd be all set up to tackle some alignment.

[Phil Nelson]

Yes, I have a 1077B TV Analyst. I guess I need to use it more often. I hauled it out, and the contacts on the channel selector seem to be funky. After letting the Analyst warm up and spending a LONG time messing with a newish solid-state TV, I was able to find a signal with the Analyst channel selector set partway between channels 4 and 5. After exercising the channel selector some more, a signal eventually appeared at its channel 4 position. It was still barely usable with the modern TV, and trying out the signal with the CTC-4 just produced a mess. Besides cleaning the Analyst's channel selector, it might help to clean its control pots.

I also have a model 415 sweep/marker generator, which I picked up somewhere in my travels and never really used. I suspect it would also need some TLC before it's ready for prime time.

Phil Nelson

[DaveWM]

Phil, are you back to the orig coil?

so in the final analysis did it turn out to be a bad detector diode?

[Phil Nelson]

I haven't reinstalled the original L42 coil yet. I did reinstall the original T115 quadrature transformer.

It seems possible the detector diode was always bad, but when first looking at that output way back when, I only scoped the grid of the 1st video amp, which gives a skeletal luma-like signal, even with a new diode. I should also have looked at the cathode of the video amp, where color information (including burst signal) appears. Perhaps the signal coming out of the video detector network wasn't as bad as I first assumed.

Since that time, I have also replaced dozens of resistors in the chrominance circuits, the video board, and the video IF board. Those replacements corrected a number of wrong voltages. It's tempting to look for a single "silver bullet" solution, but I suspect that the TV started out with a bunch of problems (maybe including a funky diode), which I'm still in the process of correcting.

Phil Nelson

[Zenith6S321]

If you have a Sencore VA62, it also puts out the color bar pattern.

Dave

[old_coot88]

Phil,
Have you checked/replaced any resistors in the IF strip yet? If not, I would start with the screen grid and cathode resistors of the three IF stages. And then check the screengrid & plate voltages of all three stages.
If all's good, then scope the screen grid of each stage. They should all be flatline. Any hash or signal of any kind on them would indicate a bypass cap problem.

[Phil Nelson]

That reminds me, I need to fix the color bars on my VA62. It makes beautiful B/W patterns, but the colors roll. Just call this the house of half-baked equipment .

In the IF section, I have replaced R115, R116, R118, R119, R120, R122, R123. That was in the context of working on AGC, and I see that it did not include the IF cathode resistors. It can't hurt to check out that section some more.

Phil Nelson

[old_coot88]

If, in checking voltages, you find any seriously out of whack on plate & screengrid of 1st and 2nd IFs, there's two honkin' 10K resistors in parallel (R320, R321). Since this pair is a B+ dropper, they could sure mess with those voltages.

[Zenith6S321]

Originally Posted by Phil Nelson

That reminds me, I need to fix the color bars on my VA62. It makes beautiful B/W patterns, but the colors roll.
Phil Nelson

You might try turning the VA62 color bar frequency adjusting capacitor screw circled in this picture. I had to adjust it on mine to get the right colors in the bars. Remove the four case bottom screws, the four rear case screws and remove the bottom cover and case cover. Remove the two screws on the top of the control panel inside the case. The top will swing backward on a hinge like shown in the picture. Its worth a try...

Dave