Simultaneous failure of horizontal output transistor and PSU transistors/MOSFETs

[japlytic]

Recently, a friend's Sony KV-XR29M31 TV suddenly stopped working.
A preliminary examination revealed that the power supply primary side MOSFETs (Q607, Q608) have gone short circuit, with a fusible 0.1 ohm resistor (R642) going open circuit (All had no visible damage).
Later examination also revealed that the horizontal output transistor (Q511) have gone short circuit (Again, no visible damage).
Replacing those components, along with C551 (with a polyester unit) and C528 fixed the problem.
But I am still wondering how the power supply primary side MOSFETs (or transistors) would short out when the horizontal output transistor shorts out?
I've encountered something just like it in an old set someone gave me to fix.

[Harvey]

Re: Simultaneous failure of horizontal output transistor and PSU transistors/MOSFETs

Your probably looking at the the wrong way - if the PSU MOSFETS short, they'd be a large enough surge to take out the HOT too before the fuse blows.

[kc8adu]

Re: Simultaneous failure of horizontal output transistor and PSU transistors/MOSFETs

heres what happens with these sony sets.
solder joints at h driver transformer crack.
this kills the hot and the resulting short blows up the psu.
these units are fussy about replacement choppers so be sure the ones you get are not remarked/counterfiet.
and pull that chassis NOW to resolder that h drive transformer and anything else suspect.or it WILL go bang again.

[Maxxarcade]

Re: Simultaneous failure of horizontal output transistor and PSU transistors/MOSFETs

I've got a Sony KP-53V25 with the RA1 chassis, that The red went out on. The red tube is ok, so I need to start looking for the next culprit.

Originally there was a resistor open on the main chassis, which was causing a feedback voltage to blow up a 160 volt cap. The set worked great for a few months until the red quit. The resistor had gone open because of a shorted output IC on the blue CRT neck board.

[tvtech]

Re: Simultaneous failure of horizontal output transistor and PSU transistors/MOSFETs

heres what happens with these sony sets.
solder joints at h driver transformer crack.
this kills the hot and the resulting short blows up the psu.
these units are fussy about replacement choppers so be sure the ones you get are not remarked/counterfiet.
and pull that chassis NOW to resolder that h drive transformer and anything else suspect.or it WILL go bang again.

He is right resolder the h-drive transistor and surrounding components for the h-drive circuit or you will keep killing the power transistors.If you need some original sony replacements I may still have a pair.Some sites had repair kits for this chassis that had them included.Also use a good HOT from a reputable dealer otherwise it could fail again very soon