You arrive at your gig and set up your gear. That funny noise your amp was making stopped when you wiggled the speaker jack at the midweek rehearsal so it must have been a temporary fault that has now fixed itself. So all is well. Not! The first song into the second set your amp makes an almighty noise then cuts out leaving a whiff of electrical burning.........
Last Saturday morning I got a call from a bass player I know - ".... my amp was playing up last night and I'm going on tour next week - can you take a look it?.....". He reported that the amplifier had been losing volume and then at one point produced no output, but the DI was still working so it looked like the fault was in the power amp stage. The amp in question was an Eden. I'd worked on one of these before and knew that they had lots of inter-PCB connectors, a possible source of intermittent problems, but I didn't have any schematics so serious diagnosis of component failure would be difficult. I agreed to take a look to see if it was something fixable.
The amp was in a flight case. As I started to undo the screws to remove it I noticed that the rack ears on the amp were both loose. When I actually removed the amp I felt something heavy move around inside! I also noticed quite a few screws missing from base of the chassis. It wasn't looking good.
Usually I would power up an amp to test for the reported fault before opening it up, but in this case I was concerned that the insides were in bad shape so the first thing I did was to take off the lid.
It didn't take too long to establish that a loose transformer had trapped a cable against the edge of a circuit board and managed to break through the insulation. The wires in question were connected to a thermal cutout switch so there was a possibility this had caused the amp to cut out.
It could have been much worse. A few more trips on the road and the transformer could have damaged the circuit board. Or the insulation on the transformer could have worn away creating untold damage. It would have been new amp time.
While I had the amplifier open I decided to give it a once over cleaning all the connectors, checking for poor or cracked solder joints and touching them up,
Unused FX Loops (this amp has 3!) are sometimes a source of intermittent problems . It is quite common for the normalising contacts on the jack sockets to corrode and interrupt the signal flow, sometimes causing the signal to cut out completely and on other occasions causing distortion when the poor contact acts as a diode. This is all easily fixed with a squirt of contact cleaner followed by a few insertions with a jack plug. Better still - leave a jack patch lead permanently connected in your unused FX loops.
Lastly I took a look at the transformer mounting. The lock nut had not actually loosened but over time the chassis had deformed slightly and the rubber gasket had compressed allowing the transformer to move around. I re-tightened the nut and bolt securing the large transformer.
With the damaged cable repaired and the missing screws replaced, tightened and secured with locking compound, the amp is fit for use and ready for another stint on the road.
If you're serious about your music, your band and your audience get your gear periodically checked. If you feel anything loose or hear any strange noises it's definitely going to get worse until it breaks. Something as simple as a loose screw can mess up a gig and cause hundreds of pounds in repairs. For just a few quid an periodic check can prevent this and give you piece of mind.