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 Sick Zenith 9-S-367

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allthumbs



Posts : 7
Join date : 2010-10-13

PostSubject: Sick Zenith 9-S-367   Wed Oct 13, 2010 6:39 pm

I don't imagine it will be too easy to locate one, but it looks like I need a bandswitch for this radio, or at least the middle of the three ganged wafers. It was playing well while on the bench, then suddenly bzzzzt -- zzapp!! Scared the $%&* out of me as it lit up the room. It is arcing from one side of the wafer to the other. It's not a case of a poor solder joint or a wire running where it shouldn't. After my pulse dropped under 100 again, I powered it up again a few times, briefly, to see exactly what was going on. The arcing is from the brass contact plate on one side of the wafer to the one on the other.

I have sent out inquiries to a number of possible old radio suppliers and have had just one reply -- he wanted $75 for it. While on the one hand I don't expect to land one for five bucks, on the other hand I sure don't want to spend what this guy is asking. So, if anyone knows of a possible source, I'd sure appreciate any leads.

Thanks!

Tom
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Johnnysan



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Join date : 2010-10-12

PostSubject: Re: Sick Zenith 9-S-367   Wed Oct 13, 2010 7:00 pm

You may not need a new switch. If you have a Dremel and the right etching tool you can dig out the carbonized traces and it won't arc again.
Did it have water on the wafer switch?
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PostSubject: Re: Sick Zenith 9-S-367   Wed Oct 13, 2010 7:07 pm

Thanks Johhnysan, I'll do that as a backup plan if I can'y come up with an undamaged replacement. Either way, I'm not looking forward to redoing all those connections!

Tom
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PostSubject: Re: Sick Zenith 9-S-367   Wed Oct 13, 2010 7:08 pm

Oops, forgot to say: no, there was never any water on the switch. It's a clean chassis for its age.

Tom
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Johnnysan



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PostSubject: Re: Sick Zenith 9-S-367   Wed Oct 13, 2010 7:20 pm

Something must have happened to cause that arcing, like moisture from moving the radio from a cold environment to a warm house.
I just hope it hasn't destroyed anything important, like an IF transformer (this happened to me with an HQ-180).
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PostSubject: Re: Sick Zenith 9-S-367   Wed Oct 13, 2010 7:39 pm

Yes, something wasn't right. I had just replaced all the capacitors and resistors, and it was playing well up to the point where the arcing began. However, despite running it on a variac set at 115vac (my line voltage is at about 121vac), I had found that the B+ voltages were high: 20 volts over spec on the plates and 10 over on the screens. The oscillator plate voltage was spot on, however. Haven't been able to figure that out yet. However, 20 volts over on the B+ surely wouldn't cause the arcing -- or would it?

Tom
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Jim Berg



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PostSubject: Re: Sick Zenith 9-S-367   Wed Oct 13, 2010 10:08 pm

I would do as Johnnysan said. At this point you have nothing to lose. Much easier (and cheaper) to fix than replace.
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k9uwa



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PostSubject: Re: Sick Zenith 9-S-367   Fri Oct 15, 2010 6:15 am

Jim Berg wrote:
I would do as Johnnysan said. At this point you have nothing to lose. Much easier (and cheaper) to fix than replace.

lots of time and good eyes to repair the switch. Possibly you used some spray electronic cleaner on the switch? It got into the bakelite and started the breakdown process. Once the arc started it was all over with in short order. You have to get past all the old black ugly stuff then replace the missing material with new high insulating epoxy carefully. If done correctly switch will be as good as a new one. I have to take the wafers out where I can use a head magnifier plus eye monicle like a jeweler uses to be sure all the black ugly is gone. Also to carefully replace the needed insulating material.
John k9uwa
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PostSubject: Re: Sick Zenith 9-S-367   Fri Oct 15, 2010 2:57 pm

Holy cow. This sounds like a real challenge. I did use de-oxit on the wafers, maybe that was the problem.
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