Audio Systems: Yamaha Amplifier AM/FM Stereo Reciever fused, output transistors, blown fuse

Question

I found a blown fuse when I opened the amplifier.  I put in a new fuse (7amp 240 v) it blew again.  This is an old Yamaha Amplifier R-100 bought in 1985.  It has been working fine with no problems till now.  Can you tell from my description what is wrong?

Answer
I can only guess.  The fuse, obviously, is to protect from excessive current.  One would have to know what is causing the excessive current.

From experience we learn that the most common causes are:

ONE:  Shorted diodes or electrolytic caps in the power supply.

TWO:  The output transistors are the culprit; either the transistors have blown or the heat washers have dried out letting too much current conduct in the outputs.

THREE:  SPeaker voice coils shorted down or short on the speaker lines.


Hope this helps you hunt down the gremlins.

C