69 Zenith 22" B&W metal cabinet

[Adam]

A strange problem: Intermittent black horiz lines across the screen.

It happens mostly when I haven't used it for a while, it would stop mostly after it warmed up for a few minutes, still doing it occasionally every few minutes for a while, stopping nearly entirely if I left it on for a few hours.

Well yesterday it got worse, and wasn't letting up even after it had been on for a while. So today I didn't use it all day, then put it up on the bench and got out the TV analyst. First injecting a signal into the tuner, bypassing the terminals on the back of the set. It was still doing it, so the problem wasn't the terminals on the back of the set. I then cleaned the IF tube sockets, as I remembered I had a problem with a dirty IF tube socket when I got this set (but didn't remember which one.) That didn't fix it. Cleaned the video out tube socket, brightness, contrast, and AGC controls, none of that fixed it.

So I figured a problem like this is probably caused by something to do with the tuner (in which I had cleaned the contacts this summer), the video IF or output, or maybe the horizontal. I disconnected the wire caring the video signal into the video out tube, and injected the video signal from the TV analyst instead. Now it stopped doing it. So that eliminates the horizontal as the cause of the problem (and the video out tube or anything in-between it and the CRT). I then did the same with each video IF tube (disconnecting the circuitry prior to it and injecting a video IF signal from the TV analyst), starting with the 3rd and going back to the 1st. But it still didn't do it again. Then I went and put the RF signal into the tuner again, and it still wasn't doing it. So it seems I fixed it and I'm not even sure what I did!

The only thing I can think of is that moving things around and soldering and unsoldering on the IF tube sockets fixed it. So I went and resoldered all the connections to the vid IF tube sockets. It's been on for about 1/2 hour now, and is still not doing it. If it still isn't doing it tomorrow morning, I'll put it back together and consider it fixed.