Resurrecting a Fender Supersonic 60 Amp

This is the tale of a fender Supersonic 60 Head almost self destructs

What Happened?

This Fender Supersonic 60 Head was a smoking amp – literally . While playing there was a strong smell of burning and smoke then the amp blew the mains fuse. 

What was the cause?

I open up the amp and there is soot covering everything.  It looked like ashes from a forest fire it is covering aall the cabling and the pcb’s. .  Soot is nice condutcive carbon so every picee needs cleared out.

The +/- 16.5  power supply volt section is  carbonised and badly burned.   I remove the the 5 watt ceramic resistors have  a better look at the damage.

Here is the view :

If you look at the schematic of this amp you can see that the HT volts which is around 410 runs next to the -16 volts supply.  The tracks are really close to each other. In my view, far to close to provide sufficient insulation as the board ages. Hey, presto, the board becomes conductive at this point and the 400 volts feeds into the power supply feeding the op amps  ( audio integrated circuits) in the front end of the amp. I am reallyconcerned that the op amps , transistors will all be damaged.  We will not know that until fix the current mess.

The Action Plan

I call Fender UK to enquire on a complete replacement PCB.  This seemed the low risk approach.  the sad new is that Fender do not support spares for this amp so no replacement PCB’s are available.

That leaves Plan B

My only option is to atempt to repair this board. I get out my Dremel drill and carefully grind away  the carbonised board.  What a smell !  I also cut the track carrying the high volts at each end. The -16 volt track had been vaporised so I repalce it with hard wire. I re-route the HT volts using wire.

The 5 watt zener diodes, 5 watt ceramic resistors and all the +/-16.5 volt electrolytic capacitors are toast and now replace them.

The Repair

Here is a picture of the repair. It is not elegant but the +/- 16.5 volts supply now works. It is challenging to replace these components because the pcb has been cooked. Great patience and care in removing the components and replacing ensures there is no more heat damage to the board.

Will the amp now work?

Now comes the big test. This is where I find out if the op amps , transistors etc have survived their possible electric shock treatment. A miracle!  Everything is good and the amp works beautifully.   I am pleasantly surprised and the big bons is that the owner gets back his Supersonic rather than a box whos only function would have been a a seat or door stop. The amp is  PAT tested just to make sure it is safe and has a good earth.