zenith 20X1C38 video noise - Videokarma.org TV - Video

DaveWM · #1 10-19-2011, 06:18 PM

tuning it to a blank screen (my converter box can do that) I get flashes of dots all across and over the screen, color dots that flash across a blanked out screen. Not a lot.

1st plan is to just run it for a while and see if it get better, maybe humidity (its out in the garage). If that does not do it I will giggle some tubes, but I don't think its that. then I was thinking of pulling the IF tubes on at a time and see if I can isolate it. If that does not do it I guess it will be scope time.

It looks like maybe a IF decoupler cap or a video decoupler breaking down.

guess it could be a load resistor as well.

Pretty sure it does it even with the fine tuning off enough to block the color, so guessing its not in the chroma at all.

DaveWM · #2 10-19-2011, 06:25 PM

ok in the time it took to type that last message, the problem resolved.

Another thing, a very slight drive line that was there when it was cold went away, hmmmm I wonder if there could relationship.

I have not seen a drive line (vert light bar 1/3 of the way across the screen from the left side viewing from in front of the set about 1" wide) resolve itself before, but then again I have rarely had drive line problems.

It all pretty much stock, I don't recall doing anything to it. I guess I should go back and check some of my post on this set.

Electronic M · #3 10-19-2011, 06:31 PM

Have you cleaned the tuner contacts in recient memory?

Dirty contacts can wreak all kinds of havock in mechanical tuners including noise, and in some cases NO signal reaching the IF. I let the contacts in my 59' Zenith get so bad that it would NOT pass a signal once, and gained a new appreciation for De Oxit.

Tube contacts can have issues too, but tuners like to do it more often.

DaveWM · #4 10-19-2011, 06:38 PM

not really that kind of noise the pic is perfectly clear, with a smattering of color flashes, but it prob would not hurt to clean it again to be sure.

Anyway it went away after a warm up. turns out this set did cause me a lot of angst, just did not remember it. it was a 23x ot a 20x1 had a whole bunch of issues (minor but there none the less).

this is the one that had the funny pin cushion problem that caused the raster to pinch in some on the bottom, was an open can cap off the vert out.

ctc17 · #5 10-19-2011, 07:25 PM

I wanna know what you find on this so I can fix both my 20x. Its like IF noise because I get it even if I go around the tuner. I gave up and deal with it even though it makes for a crappy picture compared to RCA

DaveWM · #6 10-19-2011, 08:01 PM

well it went away so I will see if cooling off and trying again I can get repeatable results. I was thinking IF or video since the pic is so clean behind it.

DaveWM · #7 10-19-2011, 08:10 PM

off for about an hour tried it again, no noise. will let is set overnight and try again.

Just to be clear this is widely displaced specks, maybe 20-30 at a time, I will see if I can capture it on a pic.

Electronic M · #8 10-19-2011, 09:12 PM

Zeniths can be funny critters when it comes to buggs. My 71' CCI hybrid once had a MAJOR width shrinkage and then lost horizontal synch before I got to the power switch. After I turned it off I imediatly set up a 40's GE fan to circulate air through it, then turned it back on after some time had passed, and there were no horizontal problems afterwards for over a year. Reciently I shorted the B+ and after fixing my careless short I was greeted by poor width. Eventually I'll dig in to her again and see if i can locate the problem.

zenith2134 · #9 10-19-2011, 10:59 PM

Hey while I do agree with Electronic Memory that poor contact connections can cause all sorts of problems, It sounds more like marginal lytics in the chroma supply are being tempermental with regards to temperature . have seen this in Fm tuners, where it displays a fault in the garage where it's cold but plays great once brought inside and inspected.

DaveWM · #10 10-20-2011, 07:41 AM

its getting colder so it should be easier to find. If I can get repeatable results I will try preheating the cans to see if they are acting up.

DaveWM · #11 10-20-2011, 11:35 AM

quick test this am, set on, drive line clearly visable, some confetti (the best description I can come up with) but very little, widely spaced, but tending toward the left hand side (this was the case before, tended more toward the left hand side) but it was there. 20min later, drive line gone, confetti gone.

since these seem to occur to at the same time (confetti/drive line) I am guessing maybe common area.

Think I will try a new damper tube.

DaveWM · #12 10-23-2011, 05:45 PM

seems to have resolved by just using it, I did get rid of the drive line by HOT sub, the confetti simply is gone, but that was even before the tube sub. I am guessing it was humidity related.

this set has a really nice pic, I will have to clean it up and get it inside. the only cosmetic issue is the speaker cloth has pulled loose (its a combo) on the bottom of the speakers. looks like major surgery to pull the speaker backer board out and re attach. Guess that would be a good time to hit the speaker wood slats with the restore a finish.

of all my zeniths this set seem to have the best pin cushion and convergence setup. There only seems to be a very slight right R/G vert touch up needed, so little that I don't feel the need to full with it and risk messing up a convergence coil.