GFA-565 problems

ben62670 · 11th August 2008, 05:39 AM

Well I have fixed these before, but this is a new problem. This particular amp had the caps on the input board actually rotted off. I did the usual U.S. cleaning with 10-1 simple green. Replaced all the input board caps, and the OpAmp. I am getting very low DC offset in the ,10mv range, but the sound is very distorted, and is only pushing, and not pulling

Any ideas? Both rails are 85 vdc, and the fuses are good.
Thanks
Ben

ben62670 · 11th August 2008, 05:50 AM

I tested the input, and it is open. I remember that on the 585 it should be about 10k?

ben62670 · 11th August 2008, 06:18 AM

10 ohms from input ground to speaker ground.

ben62670 · 11th August 2008, 06:41 AM

R135 1/4w 82r open

You should have seen how bad this sucker was. Nice, and clean now. Offset is still ,10mv. I still have another to do.
Wish me luck. If I get stuck. I'll post again.
Thanks Guys
Ben

ben62670 · 11th August 2008, 10:15 AM

Did the second one. Job went good. One crappy resistor was on the board. Looked like a Rat Shack 1/2 watt in place of a 1/4 watt metal film. Well that is changed, and the DC offset is <4mv on this one. All new caps, and an OpAmp.
Ben

Thanks Chris. I could have never done this without your help. Hope things are well.
Ben

ben62670 · 14th August 2008, 06:36 AM

Well I did two more today. I have an Adcom fetish

Both under 4mv also

Ben

11th August 2008, 05:39 AM	#1
ben62670 diyAudio Member Join Date: Dec 2006	GFA-565 problems Well I have fixed these before, but this is a new problem. This particular amp had the caps on the input board actually rotted off. I did the usual U.S. cleaning with 10-1 simple green. Replaced all the input board caps, and the OpAmp. I am getting very low DC offset in the ,10mv range, but the sound is very distorted, and is only pushing, and not pulling Any ideas? Both rails are 85 vdc, and the fuses are good. Thanks Ben

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11th August 2008, 05:50 AM	#2
ben62670 diyAudio Member Join Date: Dec 2006	I tested the input, and it is open. I remember that on the 585 it should be about 10k?

11th August 2008, 06:18 AM	#3
ben62670 diyAudio Member Join Date: Dec 2006	10 ohms from input ground to speaker ground.

11th August 2008, 06:41 AM	#4
ben62670 diyAudio Member Join Date: Dec 2006	R135 1/4w 82r open You should have seen how bad this sucker was. Nice, and clean now. Offset is still ,10mv. I still have another to do. Wish me luck. If I get stuck. I'll post again. Thanks Guys Ben

11th August 2008, 10:15 AM	#5
ben62670 diyAudio Member Join Date: Dec 2006	Did the second one. Job went good. One crappy resistor was on the board. Looked like a Rat Shack 1/2 watt in place of a 1/4 watt metal film. Well that is changed, and the DC offset is <4mv on this one. All new caps, and an OpAmp. Ben Thanks Chris. I could have never done this without your help. Hope things are well. Ben

14th August 2008, 06:36 AM	#6
ben62670 diyAudio Member Join Date: Dec 2006	Well I did two more today. I have an Adcom fetish Both under 4mv also Ben