Just thought that I would start a thread about some servicing work I'm doing on a mate's Fender SRM 6302 PA Amplifier, the complaint was that it was producing a loud hum when switched on, so I opened up the back panel and had a look inside, I couldn't see anything obvious, like burnt-out components so I decided to have a more careful look around the main PCB that has the power supply and power amp circuitry on it, making sure that the amp was completely disconnected from the mains, and that was when I noticed that one of the main power supply filter caps felt like it was a bit loose compared to the other, and I immediately knew where the cause of the fault was most likely to be, so I completely removed the back panel of the amp from the cabinet after carefully noting where wires were connected, and then removed some screws that held the PCB in place on the heatsink, then I looked at the underside of the PCB and found that I was correct, there were two solder joints on the loose filter cap that had cracked and broken so I proceeded to remove the old solder using some 3mm Goot Solder-Wick, and then re-soldered the joints, I did the same to the solder joints on the other filter cap as a matter of course, I think that should fix the loud hum fault, but I'm going to go through and test all the power output transistors with my in-circuit transistor tester first before I put the back panel in the cabinet just to be sure that all the power output transistors are still all good.
As a side note, just before I was about to put the amp back together I noticed an electrical safety-hazard that I needed to correct before proceeding any further, whoever had previously owned the amp had replaced the original 240 V AC Cable Clamp (presumably because said Cable-Clamp broke, or was missing) with a Zip-Lock Cable-Tie and some Electrical Tape which was wound around the 240 V AC cable and Cable-Tie, I have now removed the Cable-Tie and Electrical-Tape because at some point the 240V AC cable will chafe against the metal back panel and create a short-circuit, I fitted a Black Plastic 240V AC Cable Gland as a replacement, which should prevent any chafing of the 240 V AC Cable in future, making it safer, it also holds the 240V AC cable more securely too.