SMPS shuts down Sharp 21AG1-S
 

My coworker was stuggling with that Sharp 20" TV for SMPS (switching
power supply) peaking high (over 135V & SMPS shuts down on current
protect (STRF-6645 SMPS IC do this and micro not getting any power or
horizontal not started either.) TV came in with blown 3.6V zener
diode and fuse. Replaced all the must have parts (optisolator, zener,
STRF-66xx, SE115). I have no worries about the SMPS now that it is
doing 115V regulating now long as this jumper is open more on this
detail shortly.

So I helped co-worker to dig deeper into it.

The power & ground is isolated for audio, this one I opened a jumper
ahead of diode but kept the connection for the feedback circuit and
got SMPS to regulate at 115V and stay there. NOTE: audio amp has own
power and audio ground is still connected so there is no shorts there,
HOT is good.

This is where Sharp engineers got extremely creative with this flyback
"startup" design (assuming?) that I have not seen before. NEED this
one expanded so we can find the problem that kicks SMPS into shutdown.
I haven't found the shorted item yet even I checked lot of unlikely
items.

The micro & eeprom only get this power indirectly from heavesting off
ripple from the positive side of audio power via this jumper both for
the feedback circuit and the audio amp, also to a small zener near
flyback. This (audio hot side) to true cold side) "ripple" goes
through a low value resistor to a regulator which is grounded
seperately to cold ground. This regulator output is around 5V DC
assuming. I had to trace all the way!
There is second 5V circuit working but this is not for micro (via
LM7805 via seperate diode & true cold ground.)

But the "startup" I'm still stumped. The super jungle IC needs 5V and
8V to complete the start up but SMPS is not staying up. 8V is
supplied from flyback secondary winding and I think this what supplies
deflection power for the super jungle IC (jungle & micro in one).
Missing power is not letting super jungle to wake up.

What is this going on with this insanely strange design? This got me
very curious.

Thanks & cheers, Wizard