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Old 06-19-2015, 05:11 PM
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strange flat chassis Zenith problems

So for the past week or so, whenever I turned on this TV (25EC58 in the Avanti cabinet), after a few minutes I would start seeing white horizontal lines of varying thickness intermittently flashing across the screen. So this afternoon, I turn the TV on its side, and start poking around trying to locate the problem. After a few hours (I still hadn't figured out what was causing it) but it went away on its own. I figure I'll leave it apart for a while and see if it comes back. I'm hoping it doesn't, but does anybody have any idea what it was?
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Old 06-19-2015, 05:54 PM
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It came back...
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Old 06-19-2015, 05:57 PM
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And now it went away again ...
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Old 06-19-2015, 07:49 PM
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Well, I took a break to eat dinner, and watch another tv. When I came back it was doing it again. But this time I tried some resoldering on that white board the flyback hooks to, and I think that might have fixed it. I'll watch some more sideways tv for a while now and see it it comes back...
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Old 06-19-2015, 09:01 PM
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I think that did it. I've been watching it for over an hour and the problem hasn't returned.
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Old 06-20-2015, 10:25 AM
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I watched it till 3AM last night, and the problem didn't come back. But then I turned it on this morning, and it did it for about a minute, then quit, and now it seems to be working ok. This sort of thing is so frustrating, I wish a tv would either just work, or not work.
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Old 06-20-2015, 12:15 PM
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I wonder if this could be arcing problem, those can be very dependant on humidity leels and come and go.
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Old 06-20-2015, 12:15 PM
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I know it doesn't definitively mean nothing's arcing, but don't hear anything arcing when it does it. But I'll try cleaning that flyback board, as resoldering the connections on that board seemed to fix most of it, and I had a set where it was arcing right across the top of a dirty one of those before.

Now it's not doing it at all again, so I can't really do anything more to try and find the source of the problem. That resoldering on the fly did seem to mostly fix it. Maybe later today I'll also try resoldering the connections on the tripler. I've seen this problem caused by a corroded focus connection in the CRT socket on another set, but that isn't the case here. Anyway, today I think I'm going to go work on my Admiral for a while instead of messing with this all day, like I did yesterday.

Last edited by Adam; 06-20-2015 at 12:21 PM.
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Old 06-20-2015, 05:30 PM
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This may be old hat but all the 22-5001 caps must be the
new orange ones. Also be sure you dont have one of the
terminal strip grounds loose. Most common on older sets but
with all the years worth looking at.
CRT sockets were a common problem from the tube days
on Zeniths. Usually too much focus due to a bad divider, tripler,
and or 22-5001. Also in greasy humid houses. A crude
test is pull the ground straps & see if there is voltage on them.
Use a HV probe it can be over 6KV !
All they do is ground the low end of the spark gaps on
each pin. Usually the socket is discolored or there is green mung
at the pin. If you open a bad socket its obvious.

73 Zeno
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Old 06-20-2015, 06:37 PM
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start hitting stuff with a stick, you'll find it........

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Yes you can call me "Squirrel boy"
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Old 06-21-2015, 05:05 PM
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I didn't list everything I had tried yesterday afternoon. Poking stuff with a stick was the 1st thing I tried.

2nd I checked the 22-5001 caps. I had replaced the white ones with the orange drop ones along with a bad tripler a few months after I got this set back in 2010. But then I had one of the orange ones short on me last summer, and I remember it doing this the day before it shorted. So I pulled one end of each cap out of the circuit and clipped in another one, then looked to see if it made a difference. In the process of doing that I did find one of the grounds two of them hooked to to be loose, but resoldering that didn't fix the problem completely.

Then it was when I was swapping out the ones on top of the chassis that I noticed it went away, and I thought those 2 caps must be bad and that I had fixed it …. but it came back. Eventually I came to the conclusion that it didn't make any difference whether I had the new orange caps clipped in or the orange ones I had already had in there, but clipping those alligator leads on the connections on that board was having an effect. Sometimes starting the trouble, sometimes stopping it. That's when I resoldered everything on that board, and that seemed to make a big difference, but didn't fix it completely.

Today it wasn't doing it at all for a long time, but when it finally did I took the back off. I checked the voltage on those grounding straps and got between 500-1000V. And now that I knew where to listen, I could hear some soft hissing coming from the CRT socket. Because there wasn't any obvious corrosion (like there was on my 25MC33 that had a bad socket) I didn't bother to take it apart yesterday. I took it apart and there was no corrosion, but there was some black gunk on the plastic in there, which I cleaned off. Now I get no voltage on the grounding straps, and I don't hear any hissing, so I think that fixed it.

And just in case, I also cleaned off that flyback board, and resoldered the connections on the tripler. Then poked at the rest of the terminal strip grounds while watching in a mirror to see if it had any effect. I think it's fixed, but this was weird because it was one problem with 3 separate simultaneous causes.
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Old 06-21-2015, 06:14 PM
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Looks like you got this one under control, congrats !
Here is an IIRC. C line flats had 2 caps on the FBT board.
D & E line had 2 on FBT board & 3 more under the chassis.
Early runs of upright CC2 sets also used 22-5001 caps
before the switch to 4 lead caps. Always best to change them
all even if they look & test good. Just one bad you may not see
but they do cause subtle problems & stress the hoz out &
HV components.

The sockets we stocked had long leads & some push on connectors.
That way it fit all sizes & gave a factory look, very important to
me but not most others. Only other sets I remember with
common socket problems were the early RCA in line CRT sets.
Filament pins would corrode & melt the plastic on the CRT &
socket. Found lots in Admirals & Maggys, the RCA's seemed to use
a better socket. Symtoms were int slow fading of raster etc.

Enuf fer now
73 Zeno
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Old 07-04-2015, 12:31 AM
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This has to be one of the strangest and most persistent tv problems I've had. So I didn't watch this set for about a week, turned it on and the same problem was back.

First I thought it was the crt socket again, but there was no voltage on the ground straps. I even took the socket apart and ran the tv while it was doing it and I was looking at the voltage on each of the pins, to see if it was jumping up and down, but it wasn't.

I noticed that flipping the setup switch back and forth made it worse. I eventually just soldered the pins together so it was stuck permanently in normal mode. This fixed the worse problem I created by messing with the switch, but the tv was still doing it like it was before.

I finally just changed the crt socket. I didn't have a Zenith one, but I had a universal replacement one with 3' leads still new in the package. It's been on for about 30 min and so far with the new socket, it seems ok. It seems swapping in the new socket fixed it, even though I couldn't detect any more problems with the old one.
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