Adcom GFA-7000 Repair

intangible
intangible Posts: 262
edited March 2011 in Electronics
I've been shopping for a multichannel amp, and there's an Adcom GFA-7000 on Craigslist near me with a faulty channel. He describes it as "distorting easily at high volumes". I know some people here have experience with Adcom amps; do you think this would be relatively easy to diagnose and fix, or is it indicative of a serious issue that would require sending it to a (very expensive) technician?
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  • ben62670
    ben62670 Posts: 15,969
    edited March 2011
    It is kinda like a transmision on a car. It isn't something that can be trouble shot without looking at it. Where are you located?
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • Outfitter03
    Outfitter03 Posts: 563
    edited March 2011
    Come on Ben. Is your crystal ball all cloudy? Could be it needs a little time on your new cable cooker!
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  • ben62670
    ben62670 Posts: 15,969
    edited March 2011
    My whole head is cloudy. I was just reading the Charlie thread and I think I got a contact high.
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • intangible
    intangible Posts: 262
    edited March 2011
    I'm in St. Louis. I realize it will take a closer looking at to identify the exact problem. I figure the five way mono board design would make it fairly simple to troubleshoot by deciding where the bad board deviates from the others, but I've never been inside an Adcom amp before. I just want to get a general idea whether I could poke around with a multimeter, find the issue myself, then get replacement parts, or if these things are too complex for a complete amateur like myself and/or full of proprietary parts.
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  • B Run
    B Run Posts: 1,888
    edited March 2011
    Can't answer your question for you, but I can tell you I have that amp and I love it. I'd say if you're getting it for the right price it'd be worth taking the risk.
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  • intangible
    intangible Posts: 262
    edited March 2011
    Alright, I went and picked it up. The faulty channel doesn't have any burnt out resistors or fuses and the caps test good. I will look into the the semiconductors over the weekend.
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  • intangible
    intangible Posts: 262
    edited March 2011
    Swapped the bad channel and a good channel to make sure the issue was the board; the static followed the bad board. I pulled both and compared the behavior of the semiconductors; the bad board's tended to read slightly less resistance, but other than that, I can't find any difference between the two boards. Any ideas as to what to try next?
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  • intangible
    intangible Posts: 262
    edited March 2011
    Exciting new news! It would appear this amp is not common ground, despite the lack of resistance between the negative binding posts. I was treated to a lovely ear piercing screech when I attempted to press it into service as a two channel amp driving a pair of SDAs. I think this one may be headed back to Craigslist after I replace the fuses.
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