Good call, but I don't think any liquid has got into this amp, it was housed in a 19" Rack unit in use so not used as a beer table like a lot of stage combos can be.
Well, the amp is still working, I've soaked tested it for ages, power-cycled, swapped inputs, all the things you'd do to double check its OK, seems fine. I'm happy to hand it back to its owner.
I repaired a lighting controller for the same fella earlier in the year. It was for some on-stage LED Lumieres (sp?) that hang from a series of T-bars. That was a diode failure that burnt out a resistor and took out the L6598 controller chip. I found what I think was liquid ingress but but I'm not sure if it caused the fault on this occasion.
On bench at the moment is his vintage (IMO) lovely big Trace Elliot pre and power amp. This has been interesting to work on, its been long-time stored in a damp leaky shed (perfect!) and theres a lot of corrosion on parts...
This fuse had been wrapped with wire as it had blown at sometime, see more corrosion on the cans of the output transistors too?...
The bearings on the fan are totally shot, it makes a complete racket, replacements are fairly expensive but a biker chum (also a retired Electronics Tech) came to the rescue with a good 2nd hand fan of the same spec, the original is so corroded the paint has lifted. Its done some serious hours of work, this amp was used a LOT...
State of this cooling fan!
The original reported fault,
"It hisses a lot, like a rainstorm outside!" I was told is also accompanied by the 'Overload' LED by the input socket permanently illuminated which he didn't remember.
Yesterday I did a "Hmm" and scratched my hairy chin before diving in. "Observation, observation, observation before you start" a wise TV engineer told me many years ago, he was brilliant to work with too.
Aha! big dry joint on one of the smoothing cap rails, see where my pointy thing is pointing?...
Cleaned up and remade the joints on that rail. Powered up, Overload LED on but the amp works fine although there is intermittent noise breakthrough. Probing around with an insulated pointy thing I found an area of the PCB where theres 3 small transistors and three trimmer pots which I believe are used to set the overload threshold at 3 points through the pre-amp section. 'Believe' as I cant get any service info from Trace Elliot on an amp this old, however the did kindly send me a late 80's schematic (hats-off to TE) that used a similar arrangement. Tapping this area reveals hiss/hash increases and decreases in the background, ooo, getting closer perhaps.
I cleaned the pots in case they were 'noisy', no change, then I started gently squirting freezer spray around the 3 small transistors, bingo, noises drop or trigger! Aha, one of the transistors is breaking down maybe? More very gentle freezing to narrow down the fault to one transistor. Theres a lot of solder flux around this area too from the manufacture in ~1981/2.
Then nothing, no Overload light on, no hisses and pops, just a perfectly working amp! Now this is where it gets weird.
I couldn't induce the fault again, heating (small heat gun with a nozzle) and cooling (can of freezer with a tube) the suspect transistor doesn't do a thing. As a precaution I removed all 3 transistors, checked their fwd volt drops using the diode test function on my ancient DVM and cleaned the corrosion off their poor little legs then replaced them all in the same positions but not before removing all the flux with IPA, there was a LOT of it.
Spotless now...
And a day later the amp remains perfect. I know its a bit far-fetched but I wonder if me freezing the transistor/s has altered the chemistry of the large amount of flux around that area on the PCB and that was what was slightly conductive maybe and tripping the Overload sense circuitry? Or maybe the transistor was noisy/breaking down and the heat/cooling cycles has temporarily jolted it back to life? I dunno TBH.
Odd, but interesting.
)
Didn't stop it but made it less annoying.