Bad Voltage!! Bad Zenith!

[mattdavala]

Hello Everyone,

My 1966 Zenith Roundie 24MC31Z chassis TV is giving me about 45 volts AC at the antenna terminal and chassis ground. It depends on which way the TV is plugged in and the switch turned on or off.

I can't win, I can have 0 volts with the TV on, or when its off about 45 volts. Swap the plug, 45 volts TV on or 0 when its off. There is no AC bybass or safety capacitor, just a 1.5 meg resistor to ground. And its a zenith, so its a transformer chassis.

Is this safe, and if its not what do I check? The TV works fine, and I haven't blown any sparks yet connecting the TV to cable via the 300 ohm matching transformer.

How do I replace 4 convergance diodes? They are in one stack together and I do not know what type of silicon diodes I need to use.

Thanks for your help,
Matt Davala

[andy]

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[drh4683]

Here is a simple schmatic and diagram that I made up for replacing the old 212-63 selenium convergence rectifiers found in pre 1968 zenith color sets. You want to use 1n4005 (nte-116) general purpose silicon diodes (1amp, 600 PIV). I have a schematic for replacing the 212-72 rectifers for zenith color sets made between 1968- about 1978. I suggest replacing this unit even if your convergence is ok. Even if they seem ok, these leak badly reverse biased at RX100 on your vom. The 212-72 is no better, if not worse than the 212-63.

After replacing this selenium, you will be rewarded with easy to adjust convergence. Heres some pics of the job I did on a '66 zenith 25MC46 last week:

[mattdavala]

Thank you Doug for documenting and keeping photos of your progress. The schematic and pictures will be a great help. I'll post another reply after I've changed out the selinium convergance rects. Thank you again.

Matt Davala