Harman Kardon pm655vxi repair help

[lemkoo]

Hi Guys,

I need a bit of help with my PM655 Vxi unit. I bought it completly dead and I'm trying to fix it, but I've hit the brick wall and can't figure it out. The amp fries resistors R474 and R476, as well as Q430.

So far, I've replaced (as they were confirmed dead) the following, see the replacement too:

Q441 / Q442 - MJL3281AG
Q443 / Q444 - MJL1302
Q437 / Q438 - 2SC4883
Q439 / Q440 - 2SA1859
Q435 / Q436 - KSA1013YTA
Q433 / Q434 - KSC2383OTA
Q430 / Q429 - KSC945CYTA

I've also replaced the trimmers for the right channel and R439/R440 with 220Ohm resistors. It does damage the above 3 componenets, even when I plug a 100W buld into the PSU fuse.

Any feedback is much appreciated.

 

[Binkman]

I've also replaced the trimmers for the right channel and R439/R440 with 220Ohm resistors. It does damage the above 3 componenets, even when I plug a 100W buld into the PSU fuse.

Welcome to A.k.
Using a dim bulb tester from the power plug??

 

[lemkoo]

Welcome to A.k.
Using a dim bulb tester from the power plug??
View attachment 2080855

That's correct. The bulb flashes and dimms, as expected. After about 30-45 sec, the transistor goes out and the two resistors start smoking...

All of the remaining transistors in the power circuit are checked and confrimed to be working.