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Old 31st January 2007, 04:39 AM   #1
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Default Dead Adcom GFA-565 Monobloc

I have a pair of GFA-565 Monobloc amps, I bought them off ebay and received them today.

The working GFA-565 had two INAPPROPRIATE 10A fuses {unknown manufacturer} for the DC rails (correct fuses should be BUSSMAN ABC-12A/250V, SOC CES6-12A/125V, or LITTELFUSE 3AG314012/250V fuses) and one INAPPROPRIATE Bussman AGC15 fuse (correct fuse should be Bussman ABC-15/250V, LITTELFUSE 3AG314015/250V, or SOC CES6-15A/125V).

NOTE: I did not know that the working unit had inappropriate fuses until after this whole experience.

I powered up and was using the working unit (with INAPPROPRIATE fuses) for an hour, experiencing the power of the massive amplifier, and it sounded great.


Then I decided to troubleshoot the other GFA-565 unit that is broken.

I took the top cover off, disconnected the fan, plugged it in, and switched it on: nothing.

After a while, I decided to take the fuses from the working unit (INAPPROPRIATE fuses) and put them into the broken unit, to see if it would work {remember at this point I did not realize that these fuses were inappropriate}).

I installed the INAPPROPRIATE fuses from the working unit into the broken one (with the power cable unplugged of course) and plugged it in.

Next I switched on the power and the power LED lights up!

BUT immediately afterwards one of the massive 100V 35,000uF ADCOM capacitors shoots off a sharp stream of smoke and the horrible smell fills the air. The instant I saw this I immediately switched off the unit and unplugged it (under 2 seconds from being switched on). Now I see the smoke and smell the crap in the air: oh no.

I took my multimeter and (making sure I probed the terminals correctly {positive to positive, etc.} I checked the status of each capacitor. One capacitor had a charge of about 67V and the other had no charge....hmmm interesting. Here is another interesting thing, the capacitors are parallel to each other. The one to the rear of the unit has the positive on the right side, and the negative lead on the left...while the capacitor to the front of the unit is rotated so that the positive lead is on the left side and the negative on the right side. The wiring is complicated so I am not sure whether that is just the way they are positioned inside the chassis or whether some unqualified technician has accidentally reversed the polarity on these caps. I do know that some work has been done on both of these amps. The previous owner (a complete idiot to be using INAPPROPRIATE fuses) had input level controls "professionally installed." God only knows what that means...and apparently, in the service manual, it says that the 25V, 220uF electrolytic capacitors on the input PCB assembly (the one everyone has problems with) have been replaced.

After about 5 minutes, the capacitor was drained and the other one was still at zero.

I removed the fuses and saw that that two rail fuses were not blown but the AC fuse was blown.

What happened here. These INAPPROPRIATE fuses worked fine on the flawless unit but when I connected them to the malfunctioning unit, it had such a violent reaction with the capacitor smoking, making hissing noises, and probably getting ready to blow up in my face.

Once again, I DID NOT CHECK THE FUSES THAT I TOOK FROM THE WORKING UNIT AND ONLY NOW DO I KNOW THAT THE PREVIOUS IDIOT OWNER HAD WRONG FUSES. But interestingly, I think that the problem was not caused by the fuses. One capacitor had charge and the other did not charge at all.

Tomorrow I want to go to Home Depot and get the appropriate fuses and then try again. But I suspect that the exact same thing will happen.

Thoughts, comments, and HELP will be much appreciated. I will attach pictures tomorrow.
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Old 31st January 2007, 04:47 AM   #2
infinia is offline infinia  United States
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Default Re: Dead Adcom GFA-565 Monobloc

Quote:
Originally posted by mjraudio
ITomorrow I want to go to Home Depot and get the appropriate fuses and then try again. But I suspect that the exact same thing will happen.


NO STOP!
There is quite a bit af energy in this amp to alot MORE DAMAGE than has probably already been done.
From your action I would say to you - take it to "qualified Amplifer repair guy". There are others on this forum that can advise on this as well.
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Old 31st January 2007, 05:17 AM   #3
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The previous owner said that a repair shop told him that one of the giant capacitors and the rectifier diode in the power supply needed to be replaced. That information might help.

Here are pictures.

http://www.flickr.com/photos/49493821@N00/375230429/

http://www.flickr.com/photos/49493821@N00/375230430/

http://www.flickr.com/photos/49493821@N00/375230445/

http://www.flickr.com/photos/49493821@N00/375230449/

http://www.flickr.com/photos/49493821@N00/375230450/
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Old 31st January 2007, 06:53 AM   #4
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Hi again!

I do believe that the bridge rectifier (part # KBPC3504P) and that damaged capacitor both need to be replaced.

I found the exact part of the bridge rectifier and I can order it and install it.

But I have a question about replacing the capacitors. They are no longer made so I will have to use different parts.

Continuing this discussion here: Adcom 565 amplifier HELP

Can I safely replace both of the ADCOM 100V / 35,000uF capacitors with 100V / 39,000uF capacitors???


Could a malfunctioning/broken bridge rectifier be causing AC volts to go to those caps instead of DC? Perhaps that could be causing the violent reactions. And this diagnosis would agree with the repair shop's diagnosis.

Thanks in advance...
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Old 31st January 2007, 07:10 AM   #5
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You can replace the capacitors with the 39.000F/100V ones. Respect the polarity.
Change the bridge as well. Also here, make sure to connect it correctly. + to +, - to -, ~ to ~
The strip between both caps (Negative from first cap to positive from second cap is normal. Don't change that.
Make sure to test with a suitable fuse, preferably one with a 1/4 lower rating then what finally should be used.
Best is using a variac in combination with a 60 to 100W light bulb in series with one of the mains wires.

In any case, take care and check everything twice before applying power.

/Hugo
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Old 31st January 2007, 07:23 AM   #6
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Exclamation Don't use a variac or bulb without reading the service manual!!!

Can't use a variac or light bulb in series on the main with this amp unless you bypass the soft start circuit!!!!!

If you don't, you'll smoke the large ceramic wirewound that is on the soft start board.

This is noted in the service manual.

And no, the wrong fuses didn't cause the problem. Most likely, the amp had a bad cap which caused the bridge to go. Now, due to using the large fuses, you may be replacing many more parts...

I'm a bit puzzled why you powered it up when the seller told you that it needed the cap and bridge replaced.
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Old 31st January 2007, 07:26 AM   #7
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Steve,
Thank you very much for that note. I was not aware of this particular case.

/Hugo
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Old 31st January 2007, 07:35 AM   #8
Apogee is offline Apogee  United States
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No problem Hugo
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Old 31st January 2007, 07:44 AM   #9
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Default Re: Don't use a variac or bulb without reading the service manual!!!

Quote:
Originally posted by Apogee
Can't use a variac or light bulb in series on the main with this amp unless you bypass the soft start circuit!!!!!

If you don't, you'll smoke the large ceramic wirewound that is on the soft start board.

This is noted in the service manual.

And no, the wrong fuses didn't cause the problem. Most likely, the amp had a bad cap which caused the bridge to go. Now, due to using the large fuses, you may be replacing many more parts...

I'm a bit puzzled why you powered it up when the seller told you that it needed the cap and bridge replaced.

Correct, the service manual did state that....The seller said he wasn't sure about what components were broken, just what the repair shop told him... I also did not know which capacitor was broken. I am trying to acquire either an original 100V/35,000uF Adcom capacitor (used) and a bridge rectifier and change those parts. Could anything else have been damaged in my little experiment earlier?

Also, if one capacitor is obviously broken, could the other one be damaged or does it either work or not work...? What I'm getting at is...if I find an exact replacement for the broken capacitor (from someone with another GFA-565)..is it smart to just replace the broken cap? Or should I start by replacing both caps? I am on a budget.

Also, what do you think the issue is here? Broken rectifier that damaged the capacitor? Or did the capacitor go first? What is the source of this problem.

Thanks in advance...
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Old 31st January 2007, 08:31 PM   #10
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I have been disassembling the amp further...I took out the capacitors and am looking to replace both of them in addition to the bridge rectifier. Right now I pulled out the AC INPUT/BIAS TIME-DELAY PCB and am looking at it to see if there is any visible damage and there doesn't appear to be any damage at all to this component. It looks and smells fine.

How can I test this part by itself to see if it works without damaging it?

Pic is here: http://www.flickr.com/photos/49493821@N00/375850028/


ALSO: On the bottom of the amp, I found this resistor or diode sitting openly! What on earth is it doing there? I suspect that the previous owner sent the unit to a real idiot who did a bad job.

Is it a resistor? Pic is here: http://www.flickr.com/photos/4949382...n/photostream/
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