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Sony STR-KG800 blows mains fuse on switch on

I Have tested the transformer, main PSU and output amp, all checks OK
anybody repaired one of these units
I need help please



Re: Sony STR-KG800 blows mains fuse on switch on

I haven't repaired one, but if the main fuse is blowing then it seems the problem has to be the PS or main output amplifiers; all other circuits like the DC-DC converter and standby boards have separate fuses or fuse resistors. Have you tried removing he secondary connections on the transformer and powering it with no load? How did you test the amplifier? That amplifier is a little odd--it uses booster packs and only PNP output transistors; you may have to lift leads to finally find the problem area. There are power supplies on the main board, but they also have separate fusing.

Re: Sony STR-KG800 blows mains fuse on switch on

Thanks for your comments
Yes, I did lift the secondary of the transformer and the problem goes away. I am also thinking Main PSU and or power amp as I have seen all those low value resistor fuses for all other circuits
BTW the power amp uses Darlington transistors MN2488 (NPN) and MP1620 (PNP)
And as you mentioned, my next step is to disconnect the + 44 and -44v that go to the power amp. There are 2 heavy duty links on the main PCB which can be unsoldered and pulled out, but in order to do this I will have to dismantle just about all of it, that’s the project for the coming week end.
My gut feeling is the main psu and the big electrolytic caps. The problem started when I moved the unit to connect up a new TV set. Will report back once I have done this.