Hello,
A friend of mine is joining me at a benefit performance for a child with a very serious medical condition in November. At rehearsal he told me that his Polytone Minibrute is blowing fuses, and was using a little
Freedom Amp someone let him borrow.
My friend is a student with very little money and had been told by a local tech that it would probably cost $400 to analyze and fix the Polytone amp and he should just dump it.
I volunteered to take a look at it. I am good at repairing tube amps but have not worked on solid state stuff. Using my tube approach, I would look for shorts, bad power tubes, bad bias supply, arcs on the sockets, check the rectifier, diodes, power transformer, caps.
In this case, I'm thinking I should start with the power supply -- rectifier and diodes. Probably the power transistors next. In looking at the circuit boards, I observe a metal film resistor right next to the bridge rectifier that has a burnt looking area on the circuit board beneath it, as though it has been heating up. Bridge rectifier getting more suspicious?
Any advice?
Oh, one more thought. Does anyone know what size fuse is supposed to be in this amp? It has no fuse right now and I don't know if my friend
has been using the proper replacement fuse in the amp. Wouldn't it be something if the fuse just blew because it was tired and he has been replacing it with undervalued fuses?
Please help in any way you can. Value of fuse, schematic, advice in order of troubleshooting -- all appreciated.
Best regards,
Paul