redart
New Member
Hi,
I'm trying to troubleshoot my venerable Pioneer A400 audio amplifier. It started making odd sounds then the power on protection relay started taking longer than usual to click in, then finally refused to click in at all, and fuse resistor R308 (circled on schematic) starting to smolder. When I replaced the fuse resistor with a normal resistor it blew straight away (I didn't realise it was a fuse resistor initially). Presumably something has shorted - one of the output transistors maybe (Q1 to Q4), or Q5 or Q6 - driver transistors ?.
I'm hoping someone can help me troubleshoot from the attached schematic - where best to look and how to test ?.
Thanks in advance.
I'm trying to troubleshoot my venerable Pioneer A400 audio amplifier. It started making odd sounds then the power on protection relay started taking longer than usual to click in, then finally refused to click in at all, and fuse resistor R308 (circled on schematic) starting to smolder. When I replaced the fuse resistor with a normal resistor it blew straight away (I didn't realise it was a fuse resistor initially). Presumably something has shorted - one of the output transistors maybe (Q1 to Q4), or Q5 or Q6 - driver transistors ?.
I'm hoping someone can help me troubleshoot from the attached schematic - where best to look and how to test ?.
Thanks in advance.