CTC-9 tint control oddness - Videokarma.org TV - Video

DaveWM · #1 04-01-2014, 08:58 AM

I recently turned on my CTC-9 and noticed the tint control acting "funny"

it had a dead area in the middle that caused the CRT to have no color just a BW picture, rotate it toward purple and the color would come up slowly, like a control control, but no change in tint. rotate back thru the dead zone (about middle till the very end of CW) and you could get a bit of green tint control but very weak color and the fine tune had to be on the ragged edge.

I did not recall having this issue with the set in the past but it had not been on in months, so not sure if it was doing before.

Anyway the fix was in the color killer, I turned it CCW and all was fine. I did not bother to set it up at the time (no color snow on off channel) but will later.

Anyway it confused me the way it would only kill the color when the tint range was in the middle to nearly fully CW (green). I just assumed the Color killer would kill the color completely if not adjusted right. Perhaps it should and I have some defect in that circuit.

ChrisW6ATV · #2 04-03-2014, 02:01 AM

That is odd, but I have not adjusted enough color killers to have a good answer.

DaveWM · #3 04-03-2014, 08:06 AM

follow up, it does not kill the color any more (or even reduce it) when adj the tint now, BUT I was wrong about it working fine, it still lacks good range, the tint shift is slightly green to normal, but never over shoot to purple.

I tried subbing a new phase detector (6AL5) and chroma ref osc control/chroma osc (6GH8). no change. the set calls for a 6EA8 but it had a 6GH8, although I doubt that could be the problem. I did try a few other 6GH8's no change.

Its not like the range is just too green as the green shift is not that much either. I really am not motivate to pull the chassis so will prob just get some new 6EA8's to be sure its not a tube problem. Even checking the tint pot would require pulling the whole chassis.

old_coot88 · #4 04-03-2014, 10:11 AM

OOPs! Double post

old_coot88 · #5 04-03-2014, 10:15 AM

Have you DeOx'ed the tint pot?
If so, I would disconnect one end of the pot and check it with an analog ohmeter for smooth operation stop-to-stop.

DaveWM · #6 04-03-2014, 11:35 AM

OC I will def check out the tint pot, its just a bit of a pita right now as I have the set in a tight location.

jr_tech · #7 04-03-2014, 12:13 PM

The wiper of the killer pot connects to the killer circuit *and* phase detector circuit through a 10 meg resistor, which is bypassed to ground with a .047uf capacitor...perhaps the cap is leaky, or the resistor has changed value?
jr

DaveWM · #8 04-03-2014, 12:15 PM

I will note that and and check it when I pull the chassis. seems likely something is up with the color killer since it was acting odd as well.

TV Engineer · #9 04-04-2014, 11:47 AM

Have you done a color afc alignment? All that is needed is a VTVM and color signal, and it will reveal the cause of many problems in a malfunctioning receiver.

DaveWM · #10 04-04-2014, 01:14 PM

I have not, but I do have the VTVM and the Sams, so I can do that.

oldtvman · #11 04-06-2014, 01:36 PM

I had that problem on the set I just sold and it was nothing more than tweeking the agc control.

DaveWM · #12 04-06-2014, 02:44 PM

so adj the AGC fixed a tint issue where tint was limited in range? have never seen that effect before, generally it just goes from too much contrast and loss of sync to washed out looking when i adjust agc on other sets.

DaveWM · #13 04-08-2014, 09:39 AM

tweeked AGC no change.

pulled chassis checked tint pot with simpson 260 (analog VOM) all good.

checked the 130pf cap connected to tint control, good value, no leakage.

did resistance checks of burst amp, osc tube, phase detector, was a little off of course but mostly within tolerance or just out of. was thrown but the plate load resistor on the reactance control (triode of 6gh8, supposed to be a 6EA8). found a 68k where a 15k was specified, looked factory, check rca field guide, found that resistor changed value on many models, the 68k was on a CTC-11 that used a 6GH8 so I would seem that is an ok sub to be using (the tube chart shows it should be a 6EA8 in the set, but the resistor matches the tube that is installed).

seeing no smoking gun I will proceed with a check out and setup of the color AFC.
my guess is an unbalanced secondary in the burst transformer.

DaveWM · #14 04-11-2014, 10:38 AM

https://www.youtube.com/watch?v=CGk2K4NlqTQ

some video of the set in operation on the last few days of analog cable.

old_coot88 · #15 04-11-2014, 02:13 PM

That looks like it might also have a demod problem. Have you DeOx'ed/reseated the demod tube in its socket and/or subbed the tube?