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Magnavox R432 burning


Tim Armstrong

Jan 1, 1970
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.
3. 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.
4. 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.
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.

Tim Armstrong

Jan 1, 1970
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.