Magnavox 32MF338B/27 Turns Off After a few Seconds

[Paul678]

It turns on fine at first, shows something like "high definition TV"
at the bottom, then flashes the channel very briefly, and then the screen
goes blank, while the front LED is left blinking.

So the screen and inverter are working fine for certain.

I tested most of the power supply caps and diodes, and they all
appear to be fine. This is an unusually board, in that the inverter
is integrated with the power supply:







You can see kind of a burn mark in the second picture (to the right of the second transformer
from the top), but when I measured the
MOSFET on the back of the board that was under the burnt area, it seemed to
measure fine with a diode test on the DMM.

If anyone is familiar with this set, please advise......

thanks.....

[tom66]

Re: Magnavox 32MF338B/27 Turns Off After a few Seconds

It's a self oscillating supply, no controller chips here! All pure transistors, caps, resistors, etc.! We seem to be seeing a lot of these. Check the power supply outputs around those diodes. Screen stays lit?

[Paul678]

Re: Magnavox 32MF338B/27 Turns Off After a few Seconds

It's a self oscillating supply, no controller chips here! All pure transistors, caps, resistors, etc.! We seem to be seeing a lot of these. Check the power supply outputs around those diodes. Screen stays lit?

The screen doesn't stay lit, because it switches back to standby.

It's harder to troubleshoot something like this, because there are
no definite test points.....bad design in that sense.