Help: Repair Adcom power amp

Scroop Moth

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Apr 5, 1997, 3:00:00 AM4/5/97

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Adcom GFA-535 power amp has one dead channel. The internal fuse on that
channel blows out.

Is this something an amateur could learn to fix, or do I need to take the
amp to a pro? Are there any typical kinds of failure I could check out?

Perry Olsen

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Apr 6, 1997, 4:00:00 AM4/6/97

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Scroop Moth <au...@centuryinter.net> wrote in article
<aulie-05049...@ppp0050.ax.centuryinter.net>...

It sounds like you probably have a shorted output transistor. I don't know
what level of experience you have, or the type of repair equipment
available to you, so it would be difficult to determine if you could fix it
yourself. You could check for a shorted transistor in the amplifier channel
that blows the fuse. It will most likely be one that is mounted on the heat
sink. If you don't know how to do this, then you probably should take it
to a repair shop. Better safe, than sorry.

Good luck!

Douglas M. Keith

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Apr 6, 1997, 4:00:00 AM4/6/97

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If a fuse is open suspect s short in the circuit,a common sense
approach is to suspect the device that draws the most current,in most
cases the output(the workhorse)While in most amps if the output is
indeed shorted always check the load resistors for open or value
change,and bias diodes(some are series in package) also drivers,if any
of these are also bad you may destroy output so check all before
reapplying power.The channel that is shorted is a mirror image of the
good one so use the good one to help troubleshoot.Hope this helps
you.Good luck!

*4th

ra...@thelampards.net

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Sep 13, 2014, 8:27:20 AM9/13/14

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On Saturday, April 5, 1997 4:00:00 AM UTC-4, Scroop Moth wrote:
> Adcom GFA-535 power amp has one dead channel. The internal fuse on that
> channel blows out.
>
> Is this something an amateur could learn to fix, or do I need to take the
> amp to a pro? Are there any typical kinds of failure I could check out?

I have the very same amplifier that had a similar issue. after a voltage surge, the right channel made on very short ('instant') burst of tone and then quit. Found one of the internal fuses blown, replaced, and the same tone was generated so I shut it off immediately. I pulled off the grille, turned the amp back on, and found the (instant/momentary) tone was the woofer extending out fully and staying put. Turned off.

I ended up joining Audiokarma and one member pointed me to http://www.hifi-manuals.com/ where you can download manuals (owner, service, repair) for free. If got the manuals for the -535 with the intention of doing the repair myself but couldn't find the time. So, I took it to a local repair shop (fingers crossed that they knew what they're doing) and got it back a couple days and $50 later and it's perfect.

There are four 2SC2362 transistors for each channel labeled Q601, 603, 605, and 615. Q601 was the failed one in my case.

Cydrome Leader

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Sep 14, 2014, 5:55:50 PM9/14/14

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timely reponse there, but for anybody else-

The great part about two channel amps is if one side is blown, you can
compare components to the other good channel.