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Magnavox R432 burning

Attached is the schematic of a Magnavox chassis, I am experiencing trouble with the resistor R432 burning. The symptoms are:

  1. plug in the TV, the turns on and R432 starts to get very hot.
  2. The screen is blank (sometimes just very dark), and no sound.
  3. If I turn the TV on, the sound comes on and the TV plays fine and R432 stops getting hot.
  4. The voltage on the base of Q402 changes when TV is shut on and off, so it appears to be a problem that is in the schematic attached.
  5. If I turn the TV off (screen darkens and sound shuts off), R432 starts to get hot again and will burn up.

What I have did:

  1. Replaced IC410 and C432 (filter cap).
  2. Did simple ohm meter short-out test on Q402, Q420, and Q400
  3. Checked values of all resistors around IC410
  4. Replaced C431.

My (current) guess:

  1. That Q402/420 is bad, can a transistor be bad, even if it passes the normal 'diode' test?

My main business is computer repair, but I have had so many inquiries to repair some TVs that I thought I would start taking on some extra business. I have not repaired TVs (used to repair all the time), in about 15 years so I am very rusty. Any help would be greatly appreciated.

Reply to
Tim Armstrong
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Yes the regulator bypass transistor can be bad and still pass the diode test, and it usually does. It is the TIP transistor that will be bad if the regulator went bad due to the capacitor being left in the set too long. See why it is better to get things fixed when they first start acting up?

One capacitor, which does exhibit symptoms especially on cold turn on, turns into a capacitor, regulator ic, regulator transistor, burnt resistor, maybe a pico fuse and horizontal output transistor.

Reply to
dkuhajda

Thanks to everyone in the group for the help on this repair (this took multiple posts), it ended up being Q400. I couldnt have troubleshot this without everyones help! Thanks again.

Reply to
Tim Armstrong

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