Adcom GFA-555 - Need troubleshooting assistance. - diyAudio
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Old 9th February 2009, 12:56 AM   #1
randar is offline randar  United States
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Default Adcom GFA-555 - Need troubleshooting assistance.

I'm trying to help a friend troubleshoot a problem with his GFA-555 (not MKII, the one with the flat faceplate and handles).

The amp powers on and you can hear music on both speakers, but the sound is very soft, even with the volume turned up to what would normally be very loud. The output also sounds like low end frequencies are being filtered out.

Is this a symptom that anyone has seen before with this amp? After reading through all of the postings on this forum relating to the 555, I didn't see anything with these symptoms.

We do have the service manual and the output voltage of the power supply corresponds with the voltage indicated on the schematic. The caps were replaced a couple of years ago for what it's worth.

What other components would cause both channels to have the same symptom. My first thought was the power supply, but that doesn't appear to be the case. Maybe something on the input stage?

I'm by no means an expert, but taking measurements and replacing components is well within my grasp, but troubleshooting components is a little over my head.

If you guys have any ideas, that would be grate!

Thanks!

Tony
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Old 29th March 2009, 03:05 AM   #2
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Default adcom gfa 555

Hello, I have the same problem with my adcom gfa 55 power amplifier.
I have buy used from my friend.
Have you solved this problem?
can you send me service manual ( I haven't!) ?
Let me know please. Kindly Roberto
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Old 29th March 2009, 06:27 AM   #3
djk is offline djk
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Check and see if the cap in the feedback loop to ground is open.
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Old 29th March 2009, 01:23 PM   #4
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Hello, can you explain better please ?
Kindly Roberto
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Old 29th March 2009, 02:02 PM   #5
SY is offline SY  United States
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If it's in both channels, it's unlikely to be electrolytic in the feedback loop.

Maybe S1 (the stereo/mono switch) has developed a problem? If you don't use the strapping (mono) option, you can just remove that switch.
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Old 29th March 2009, 06:00 PM   #6
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Yes , soft sound in both channels and first model with the flat faceplate and handles ( no MK II)

I haven't never use the stereo/mono switch, but it's unlikely to be the switch mono options.
With service manual guide I can control voltage parameters.
There is a member that send me service manual please?
I will keep informad.
Kindly Roberto
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Old 29th March 2009, 06:03 PM   #7
SY is offline SY  United States
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The schematic is quite available. With that, you should be able to trace things down pretty easily.

http://www.diyaudio.com/forums/attac...amp=1142458830
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Old 29th March 2009, 09:09 PM   #8
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Thank you but I need manual for complete information of the power amplifier. My email is:

blobbulobis@inwind.it

Kindly Roberto
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Old 29th March 2009, 09:27 PM   #9
djk is offline djk
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You look at the board, you look at the schematic. What do you need that isn't in the schematic? Not that much to this circuit.
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Old 29th March 2009, 11:00 PM   #10
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Ok, thank you.
Kindly Roberto
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