adcom gfa-555 repair help sought-va local expert?

[rstillin]

I've had this amp "professionally" repaired once. After getting the amp back I hooked it up to my system (15" sub) and noticed popping noises with no input signal. Since I dropped almost $200 on the repair I promptly took it back to the shop for additional service to complete the repair. After getting it back the 2nd time it appeared all was good.

Fast forward 6 years later and it's not working again. The left channel distortion light is on, one of the output fuses (6a) was blown, and there is a smell of warm electronics where powered on. I opened it up and immediately saw a few obvious issues. The first question I have is; should I bother with a repair? Second question is are there any local experts willing to walk through the repair with me (I'm in the DC metro area)?

I've pointed out the items that appear to have been replaced under previous repairs with "star" symbols in the first image. The obvious issues are highlighted with "arrows". The 2SC2240BL at Q1 that is split in two is clearly going to cause problems

Additional options I'm considering:

sell the amp in the current condition
build a new amp using the chassis, power supply, and other good parts in the amp
replace every component in the amp (I have no test equipment other than a fluke 73III multimeter)

thanks in advance for your help!

Ross

 

[PreCD]

With being armed with only a multi-meter I would suggest selling as-is letting the buyer know what you have told us. Randomly replacing parts in the amp will, in the end, have you chasing your tail around like a dog. If you want to keep the amp let someone with the tools necessary to troubleshoot the problem have it......you will be thankful you did in the end.

Other option is to educate yourself, buy the necessary tools, and have a go at it after that. Long process but would be well worth it in the end.

 

[rstillin]

With being armed with only a multi-meter I would suggest selling as-is letting the buyer know what you have told us. Randomly replacing parts in the amp will, in the end, have you chasing your tail around like a dog. If you want to keep the amp let someone with the tools necessary to troubleshoot the problem have it......you will be thankful you did in the end.

Other option is to educate yourself, buy the necessary tools, and have a go at it after that. Long process but would be well worth it in the end.

I guess I was thinking about reconditioning the amp. I understand tracing down a particular failed component is not likely without the proper equipment, and firing up an amp with failed component can lead to new damage. What about replacing all of the transistors, fuses, capacitors etc. Assume all the components are replaced in the input pcb and output boards. Do you need test equipment at that point?

 

[WithTarragon]

Realistically, this could get expensive to fix and, depending on the specific problem, is probably beyond your skill level. They are good amps, but they are older and could probably use some re-freshing anyway.

Working ones frequently sell for about $300 on CraigsList. Even those would benefit from replacing the electrolytic caps (big and small). If the amp is working and the DCV output is less than a few 10's of mV on each channel, then re-freshing the caps and verifying the bias is appropriate. You can certainly find working GFA 555 amps that would fit the bill. The cost of fixing a broken one does not make sense. Labor is expensive.

BTW, simply replacing parts until it works again is not a good strategy.

 

[rstillin]

any comment on reusing the amp in a new DIY project? I'm pretty sure the power supply and caps are in good condition. The case and heatsinks, binding posts etc are all good. My understanding is the PSU outputs +/- 81v with a 700VA rating.