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Old 6th May 2016, 09:00 PM   #1
diyAudio Member
 
Join Date: May 2016
Default preventative maintenance for Adcom GFA-555 ?

My first post.

Just bought a working Adcom GFA-555 mk1 for $160.
It is setup 220v (I have pamplet to change it
back as well as the service manual)

I figure I'll check for too much DC output and
hookup to some cheaper speakers first.

But, given the large number of posts on here
from people with one or both channels broken and
about leaking caps with conductive electrolyte,
anything else I should do on it other than
inspecting for visible leakage? Does anyone have
a cap kit?

Don't want to get into modifications yet.


Thanks,
Allan

(skill level: have built own loudspeakers,
moderate amount of electronics tinkering,
have replaced lots of components, recapped, have
metcal soldering and desoldering stations,
scopes, analyzers, etc. Have the normal
Mouser/Digikey/Allied books)
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Old 7th May 2016, 05:13 PM   #2
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Welcome.

Why not replace the caps as a preventative measure? Maybe replace with higher voltage, higher temperature versions to try and gain some margin against leaks?

You could also paint varnish on the PCBs under the caps should they leak. ...or melt wax. Something to prevent absorption of the electrolyte, should the caps leak. It's be nice if someone could copy the layout and fab the boards in FR-4 (fiberglass) material, instead of the paper mache like material that Adcom settled on. It must have been a cost move.

Having repaired a few after the leak, I can tell you it is a big pain in the *** and a little bit of work up front to prevent the issue would be well worth it.
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Old 13th May 2016, 06:17 AM   #3
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Ok, looking over it, none of the caps looked bulged
or leaking like I've seen before on others (which
is not always an indicator; I've pulled dead ones that
looked perfect).

Should I replace just electrolytics or the silver mica and
film ones too?

DC offset (with no input after warming up 10 minutes)
is 44mV L and 29mV R

Last edited by achong; 13th May 2016 at 06:44 AM.
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Old 15th May 2016, 09:41 PM   #4
BTG is offline BTG  United States
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What driver transistors does it use? They are the TO220 package parts. Earlier ones were under rated and went bad often.
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Old 15th May 2016, 10:36 PM   #5
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It sounds like your ok.. - but, I would replace the electrolytic caps on the pre board. Be sure to clean the board up, removing any conductive electrolyte!
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Old 16th May 2016, 10:05 AM   #6
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Quote:
Originally Posted by BTG View Post
What driver transistors does it use? They are the TO220 package parts. Earlier ones were under rated and went bad often.
mine say A1210 (2 of them at Q7) and C2912 (2 of them at Q4)
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Old 29th May 2016, 07:26 PM   #7
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I replaced with some nichicon fg and kz from mouser, and DC offset stayed the same (30mV). It's only 5-6mV when input is plugged in.

I'm replacing the broken switch and adding some heatsinks to the transistors on the input board, and other than that, think it's good to use.
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