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Alrighty, I've been working away at this set and while it has not had power applied since my first posting, it is looking pretty good.
The deadly short wasn't obvious at first. The previous owner was a Zenith service tech, and he said he gave up on it after a power diode shorted. Well, after replacing caps and diodes, I still had a breaker fault. tracing through the circuit, I found on the B+ line a ceramic cap that had been twisted repeatedly, shorting out its terminals to ground. Hence the tripping breaker. The guy said his kids hated the tv, maybe one of them decided to kill it.
There were a lot of repairs. Mostly new electrolytics stacked on top of eachother. A pair of wirewound resistors in the Vertical section were dangling due to cold soldering welds. Since they weren't hooked up, I removed them and traced out the circuit, replacing a resistor and a cap and now it matches the schematic.
With this done, I have begun testing resistances at different pins and I have found some items that do not match the schematic:
First, the brightness control is coupled to the cathode follower, before the delay line. On my SAMS, it is attached to the Video output tube after the delay line. As a result, several components are not present in my set and my readings differ considerably here.
Another curious item I found is that the cathode of the 3rd video IF tube is supposed to be coupled to ground through a small resistor. Well, the resistor is there, but rather than being coupled to ground it is attached to a diode whose other terminal goes to ground. This diode is not in my schematic at all. What is its purpose?
Other than some small differences in some components, it seems good. I am mostly concerned with the above modifications, ie that they were part of earlier repairs, etc. If anyone has any ideas if I should be concerned about these differences, I'd be happy to hear them. Oh, and Happy Easter, everyone.
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