Today's Mystery Guest (RCA CTC-4)

[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

[Phil Nelson]

Ah, I remember that convertible-top chassis. When I first got the VA62A it had a bad ripple, which I fixed by replacing a couple of p-s electrolytics.

That is one heckuva twitchy adjuster, or else there's something else going on that makes this oscillator circuit unstable. After much careful tweaking with my longest diddle stick, I was able to get the rolling to snap into regular color bars. When I put the case back on, colors went back to rolling.

The ripple has also begun to resurface. I have gotten a good in-circuit cap checker since I bought this thing. While it's on the workbench, I may as well check the other electrolytics and see what else has gone bad in the last few years.

Phil Nelson

[DaveWM]

any updates Phil, last time looked like you were getting close.

[Phil Nelson]

Still grinding along with the resistor hunt. The audio's great and I can tune in a halfway-decent picture with difficulty. I can make bright and correct NTSC color bars, but things fall apart when viewing real program content. I suspect I'll soon hit the wall and conclude that the TV will never look good without a full RF & IF alignment, something I'm not equipped to do.

Phil Nelson

[DaveWM]

seem like you can confrim that if you feed it a ntsc signal to the video amp (if correct and strong enough anyway).

I have done alignments on color sets with a BK415 did not make things any worse so I guess I did it right.

problems I generally had was not getting a wide enough band pass so had issues getting the traps set (traps often fell well outside of the curve, so could not trap anything. Don't know if the built in markers would work with a CTC4 either. I would prob go with a variable marker and a freq counter for that set.