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Old 05-21-2018, 08:45 AM
Jon A.'s Avatar
Jon A. Jon A. is offline
Don't mess with Esther.
 
Join Date: Jun 2013
Location: Canada
Posts: 4,267
Quote:
Originally Posted by mrjukebox160 View Post
Look for a bad 20-30 volt zener in the "x-ray protect" circut.
Not sure if this one was meant for me as I don't know of a circuit by that name but I got out the manuals and found a 1N4741 on the horizontal oscillator board and an interesting tidbit in the circuit description:

Quote:
Transistor Q564 and associated circuitry make up a failure indicator device for detecting when there is a failure in the high voltage section, which allows the high voltage to increase beyond a predetemined level.

Zener diode ZD567 prevents Q564 from conducting until the base reaches 10.6 volts or more. The voltage divider; consisting of resistors R583, R584 and R585; ensure the Q564 is off unless the voltage sampled from the flyback increases sufficiently to bias Q564 on. When Q564 is conducting, it pulls the horizontal out of sync and cannot be reset until the high voltage section is repaired.
It makes sense to me now why that zener diode could be the culprit. I'll certainly try the variac trick when I can. Sometimes I can turn the horizontal hold control lock-to-lock and get the picture to snap back in but it never stays. I saw degaussing instructions in one of the manuals, I'll have to go over the whole darn thing once I do get a proper coil instead of trying to rig up a potential fire hazard. Considering a discussion I saw here fairly recently I'd say the power relay is magnetized and has gotten worse since I got it. I usually have to push the power button quite a few times before it will turn on or off, and often times the set will turn on the instant it's plugged in.

Oh, and on the subject of snowy pictures: this set had that problem as well and the AGC control had little effect. Then I found the RF bias control on the AGC/sync board and adjusted that slightly; presto, no more snow. Get off my screen and onto the ground, thank you.

Back to our regularly scheduled programming.

Last edited by Jon A.; 05-21-2018 at 09:02 AM.
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