Fender Frontman 212R repair attempt

[Whisper 74]

I’m trying to repair a 212R for a friend. I’m aware of tube technology but new to SS. The amp was only doing loud hum. I checked for DC and/or ripple on output (after reading Enzo ). DC present, no ripple. Pulled out Q18/19/20/21 and they’re not shorted.
I had a look to the board, R84 was fried, as well as R89 and 90. Everything else looked ok tested in circuit except Q11. I desoldered it and tested it out of circuit and it was gone too. So I replaced it.
I then tried to fire up the amp without Q18 to 21 to check some voltages (as suggested in another forum) and R83 burned !
I’m stuck at this point ...

[Jon Snell]

Very odd, I would suggest either a solder bridge or technician error.
R83 is not connected to the output transistors directly and I can think of no reason for R83 to burn up.
I cannot suggest a method as I am not working on it but, never remove transistors on a whim as this can cause issues when powered up.
If the output transistors were OK, I would firstly disconnect any loudspeakers, check the power supply is balanced and confirm the DC voltage on the loudspeaker connector.
Check any resistor marked as fuseable, (Fu) Always replace with the exact same type and value!

[Whisper 74]

Thanks Jon. So I assume I have to put the 4 output transistors back into place first, replace R83 and fire it up again to check voltages ?

[Whisper 74]

I forgot the schematic

[Enzo]

Work without a load until the amp is stable and NOT making DC on the output.

Build and USE a light bulb limiter.

[Jon Snell]

Thanks Jon. So I assume I have to put the 4 output transistors back into place first, replace R83 and fire it up again to check voltages ?

If, and only if they are testing OK put them back.
Try and find out why that resistor burned up as it makes little sense.
As Enzo says, use a current limiter. That will save lots of components and fuses blowing and ALWAYS use a mains isolating transformer for your own safety!

[Whisper 74]

Ok, I’ll try that. I have a bulb limiter as well as a variac.

[Whisper 74]

I can’t find any 1/4w fu47 or fu470 resistors. Starts at 1w but if it has to blow at 1/4w ...

[Whisper 74]

Found them here : https://m.donberg.fr

[JanV]

Did you succeed in repairing the amp? I have run in to the same problem it seems and if you could tell me what you did to fix it i would be very grateful.