CT-100 color sync issue?

[Phil Nelson]

I should clean house more often. I was rummaging through junk boxes and found these:



The cases are identical to the original, although the legs are a little thinner and closer together. The original has the codes 1107330 -1 4-54. These are stamped ED and have codes 1107863 -3 3-66 and 1107863 -1 4-77. If the last three digits are date codes, then maybe I have one from each decade.

I'll bend/thicken the legs on one of them and try it out.

I'm going to build the video preamp described in the 1956 RCA Broadcast News article so that I can bypass the front end. If the problem disappears, that tells us it was located upstream, I guess.

I also ordered some 100% DeOxit and leetle brushes to see whether cleaning the front-end sockets helps.

Phil Nelson

[Phil Nelson]

I got a new NTE358 crystal and cleaned all sockets the Pete way. Cleaned the tuner, too, while I was at it.

The original crystal was certainly off frequency, judging by what happens when you swap crystals without changing anything else. Assuming the new one is correct, the other old crystals that I found are also off by varying extents.

I redid the color AFC alignment with new crystal in place. The picture is strong and noticeably more stable than before. I think the cleaning was well worth the effort. We still have evil color bands, though.



I turned contrast & brightness way down on this one to show how stable and well defined the color bands are.



Maybe I'm messing up somewhere in the color AFC procedure. The darned thing feels like it's so close to locking . . . .

Phil Nelson

[miniman82]

Did you get the one I sent you?

[old_tv_nut]

Originally Posted by Phil Nelson

I turned contrast & brightness way down on this one to show how stable and well defined the color bands are.



Maybe I'm messing up somewhere in the color AFC procedure. The darned thing feels like it's so close to locking . . . .

Phil Nelson

There are 10 (maybe 12 with vertical retrace) color bands, meaning the oscillator frequency is off by 600 -720 Hz. So either the oscillator frequency is tuned this far off and the AFC can't pull it in, or there is something wrong with the phase detector [edit - or the reactance tube circuit] that is forcing it off to one side.

[Phil Nelson]

Originally Posted by miniman82

Did you get the one I sent you?

I did, thanks. I was able to find a new one after all, so I can return this one to you.

Regards,

Phil

[yagosaga]

Is there a chance to tune or detune the reactance control until the color bars are in sync?

[miniman82]

Originally Posted by Phil Nelson

I did, thanks. I was able to find a new one after all, so I can return this one to you.

If I needed it, I wouldn't have sent it to you. Go ahead and keep it.

[Pete Deksnis]

Phil,

Wondering what happens when the color AFC is aligned using the DVD/Dorothy signal as the input...

Pete

[Phil Nelson]

Originally Posted by yagosaga

Is there a chance to tune or detune the reactance control until the color bars are in sync?

You can access the top of the reactance transformer, 2T124 in the RCA manual ( http://antiqueradio.org/RCACT-100Tel...Service_Manual ). Is this what you're referring to? That adjuster is named A40 in step 37 of the Sams alignment instructions, http://antiqueradio.org/art/temp/RCA...structions.jpg .

Turning that control while watching the screen, I can change the number of bars but not eliminate them.



I wonder if the frequency is too far off to bring into locking range by that means . . . .

Phil

[Phil Nelson]

Originally Posted by Pete Deksnis

Wondering what happens when the color AFC is aligned using the DVD/Dorothy signal as the input...

I recently made a test pattern DVD, so here are color bars from that DVD. I didn't change anything else since the previous photo except to switch the channel and adjust fine tuning a bit.



The generator input and DVD input seem to give roughly the same result. I may as well use the DVD on the next go-round, though.

Phil

[old_coot88]

Originally Posted by Phil Nelson

You can access the top of the reactance transformer, 2T124.... Is this what you're referring to?

Phil, that adjustment should bring the osc. into sync. See if it will lock in solid, or if it still has 'weak' sync. Bill(oc)

[Phil Nelson]

I'm not entirely sure what you mean by weak sync, but I can get it to lock on a set of horizontal color bands. They don't roll vertically. Moving that adjuster in one direction makes more bands. Moving it in the other direction makes fewer bands. In between the stable points, the bands roll. Continuing in the fewer-bands direction, the adjuster runs out of travel before you reach the Good Place.

Maybe something fishy upstream . . . ?

Phil

[old_coot88]

Phil, what does it do with the original crystal in place?

[Phil Nelson]

Bill, do you have ESP? About 20 seconds ago, I just finished uploading this fresh picture of the TV with original crystal back in place.



Colors aren't perfect, but we're back in the game.

I'm not sure what possessed me to try the original crystal, since I was so convinced it was bad. Couldn't think of anything else to try, maybe.

I should quit tormenting this poor old thing and just watch a movie for a change

Phil

[jr_tech]

In the first post on this thread the color bars from the generator looked fine but the DVD exhibited off-frequency color frequency of perhaps 120 Hz... Is Dorothy looking good now?
jr