Hi Ben,
I used an ultrasonic cleaner and about 10:1 mix of water and Simple Green. Remove the bias controls and capacitors before the cleaning.
Sorry, it's a pain but that is what you need to do. That electrolyte is tenacious stuff. It ignores several other electronic PCB cleaning agents. Blow the water out with compressed air after the final rinse. Make sure you get under the IC's and resistors too. Also the foil side.
-Chris
I used an ultrasonic cleaner and about 10:1 mix of water and Simple Green. Remove the bias controls and capacitors before the cleaning.
Sorry, it's a pain but that is what you need to do. That electrolyte is tenacious stuff. It ignores several other electronic PCB cleaning agents. Blow the water out with compressed air after the final rinse. Make sure you get under the IC's and resistors too. Also the foil side.
-Chris
GFA-565 to come soon...
Wow, I just read through the 7 pages of this post and I have a lot to think about now.
This is off-topic but I just want to introduce myself into this conversation without taking too much away from Ben's problem with the GFA-565's stereo brother, the GFA-585.
I just bought a pair of Adcom GFA-565 monobloc amplifiers. One is working and one is broken. The previous owner said that "I attempted to repair the amplifier, but the service was not completed because the 35000mfd capacitor is no longer available from Adcom. It is a specific part for the Adcoms and is not used in other brands. The repair shop's quote was for about $240.00 to replace the cap and a rectifier diode in the power supply. The initial estimate for repair was to replace the cap and rectifier diode only."
I have been searching google and eating up anything on the GFA-565 internal components and diy fixes for them.
When I receive it, I am going to prod inside (carefully) and take some high-res pictures of the boards and try to find the problem.
I want it to be a learning experience and I want the satisfaction of fixing it myself. But I anticipate needing some guidance from the more knowledgeable and experienced audio experts here (i.e. Chris 🙂)
I will post a new topic when I have my gear and have made my initial look at it. But I just wanted to say hi to everyone and let you know that I'm keeping a close eye on this topic and also reading through other Adcom-repair-related posts on this site as well as others.
I look forward to chatting with you guys and wish Ben the best of luck with the 585.
Wow, I just read through the 7 pages of this post and I have a lot to think about now.
This is off-topic but I just want to introduce myself into this conversation without taking too much away from Ben's problem with the GFA-565's stereo brother, the GFA-585.
I just bought a pair of Adcom GFA-565 monobloc amplifiers. One is working and one is broken. The previous owner said that "I attempted to repair the amplifier, but the service was not completed because the 35000mfd capacitor is no longer available from Adcom. It is a specific part for the Adcoms and is not used in other brands. The repair shop's quote was for about $240.00 to replace the cap and a rectifier diode in the power supply. The initial estimate for repair was to replace the cap and rectifier diode only."
I have been searching google and eating up anything on the GFA-565 internal components and diy fixes for them.
When I receive it, I am going to prod inside (carefully) and take some high-res pictures of the boards and try to find the problem.
I want it to be a learning experience and I want the satisfaction of fixing it myself. But I anticipate needing some guidance from the more knowledgeable and experienced audio experts here (i.e. Chris 🙂)
I will post a new topic when I have my gear and have made my initial look at it. But I just wanted to say hi to everyone and let you know that I'm keeping a close eye on this topic and also reading through other Adcom-repair-related posts on this site as well as others.
I look forward to chatting with you guys and wish Ben the best of luck with the 585.
Hi mjraudio,
Welcome to the forums.
Please keep in mind that while it's great to be able to repair your own amplifier, these are rather more complicated than the normal amp. There is more energy hanging around to lay waste to probes, new parts and PCB foil. Please proceed carefully and know when to turn the work over to a qualified tech (who has years of training).
If you need to replace output transistors or diff. pairs, you will need to buy many more parts than you need and some method to obtain a matched pair from that sample. Also know that if you can't you need to buy more. Do it right or you're wasting your time.
If you can do these things, then give it a go. Don't read tweaks until you have it repaired in stock form. Study long and hard before attempting to change the original unit.
-Chris
Welcome to the forums.
Please keep in mind that while it's great to be able to repair your own amplifier, these are rather more complicated than the normal amp. There is more energy hanging around to lay waste to probes, new parts and PCB foil. Please proceed carefully and know when to turn the work over to a qualified tech (who has years of training).
If you need to replace output transistors or diff. pairs, you will need to buy many more parts than you need and some method to obtain a matched pair from that sample. Also know that if you can't you need to buy more. Do it right or you're wasting your time.
If you can do these things, then give it a go. Don't read tweaks until you have it repaired in stock form. Study long and hard before attempting to change the original unit.
-Chris
I would like to add that the 565/585 are not good amps for the beginner to attempt repair as they are very difficult and very dangerous to work on. When I was at Adcom, there was only one person who knew how to work on these, and even he didn't know exactly how the amp worked. After he left, I was the guy who worked on these and it was long after I quit that I understood how these worked.
Regarding some of the other posts on this thread:
As I recall, the 565 had two floating grounds one 10 ohms and the other 100 ohms. From the ground pin on the line cord to the negative speaker terminal you should measure 100 ohms. From the ground pin to the input rca negative you should measure 110 ohm. Finally from the input rca negative to the negative speaker terminal you should measure 10 ohms. Hums and buzzes form this amp are usually because the 10 ohm and 100 ohm fusable resistors are bad. This is often caused by grounds being connected. As I recall (and it's been a long time) there was a specific fix for the polk SDAs that involved an extra speaker cable. I think polk had a special cable just for this problem. I think the 585 was also floated the same way and prone to the same problems, but I'm not 100% sure.
A little trivia - there were only 3000 GFA-585s made worldwide.
The 565 that is not working may be an easy fix if the amp turns on, the power LED and two green LEDs on the input board are lit, but there is no output (and also no offset). If that is the case, please contact me privately for the fix.
The GCA-510 was not particularly rare, but was for export only. It is essentially a SLC-505 passive line controller inside a GFA-535.
Cheers,
Regarding some of the other posts on this thread:
As I recall, the 565 had two floating grounds one 10 ohms and the other 100 ohms. From the ground pin on the line cord to the negative speaker terminal you should measure 100 ohms. From the ground pin to the input rca negative you should measure 110 ohm. Finally from the input rca negative to the negative speaker terminal you should measure 10 ohms. Hums and buzzes form this amp are usually because the 10 ohm and 100 ohm fusable resistors are bad. This is often caused by grounds being connected. As I recall (and it's been a long time) there was a specific fix for the polk SDAs that involved an extra speaker cable. I think polk had a special cable just for this problem. I think the 585 was also floated the same way and prone to the same problems, but I'm not 100% sure.
A little trivia - there were only 3000 GFA-585s made worldwide.
The 565 that is not working may be an easy fix if the amp turns on, the power LED and two green LEDs on the input board are lit, but there is no output (and also no offset). If that is the case, please contact me privately for the fix.
The GCA-510 was not particularly rare, but was for export only. It is essentially a SLC-505 passive line controller inside a GFA-535.
Cheers,
woodman said:
You are correct about some model Polks SDA's. They designated the cable "A1" and this was for non-common ground amps, I believe it had an isolation tranformer built into it. They have long been unavailable from Polk and there is a DIY version available, but it's not as good as the original. In talking with Ken Swauger, the head CS guy at Polk the main reason the DIY units aren't as effective is the transfomer Polk originally used is no longer available and there is no such thing as an 'exact' replacement.
There has been some discussion over at the Polk forum www.polkaudio.com about this issue for those who might be interested in more info.
You wouldn't happen to have a schemantic for the GCA-510? I have one that someone previously fooled with and it has issues. I'd like to get it repaired, but have no idea who would do the right job. I'd love Anatech to take a look at it, but since I live in the states and he's in Canada it might cost alot to ship back and forth.
Brock
JamesW, Thanks! I'm tracking them on DHL and I will get them next Thursday.
Will post pics and my initial report then. I hope that it can work.
If I am able to fix the broken amp I think I will also want to replace the electrolytic capacitors on the input board of the other amp to prevent future problems.
What brand/type do you recommend?
Will post pics and my initial report then. I hope that it can work.
If I am able to fix the broken amp I think I will also want to replace the electrolytic capacitors on the input board of the other amp to prevent future problems.
What brand/type do you recommend?
cleaned the boards again... .9 volts DC... offset... Bias stable at 24mv... checked the ohms again 110 ,and 10 both good on both sides... 
Is it bad for the amp to run it at .9 volts offset? It sounds good, just out of spec.
Thanks again, Ben
Is it bad for the amp to run it at .9 volts offset? It sounds good, just out of spec.
Thanks again, Ben
ben62670 said:cleaned the boards again... .9 volts DC... offset... Bias stable at 24mv... checked the ohms again 110 ,and 10 both good on both sides...
Is it bad for the amp to run it at .9 volts offset? It sounds good, just out of spec.
Thanks again, Ben
Maynot be bad for the amp, but you aren't doing your speakers (especially the tweeters) any favors. 😱
Electronic crossover, running the tweets on a seperate amp(GFA-7500) One volt pushes the cones out ever so slightly on the 8 woofers per cabinet.
Hi Ben,
Install shorting RCA plaugs into the amp inputs, disconnect all speakers.
Turn it back on and measure the DC offsets. Anything over 50 mV is broken. DO NOT CONNECT THE SPEAKERS IN THIS STATE!!!!!!!!
-Chris
Install shorting RCA plaugs into the amp inputs, disconnect all speakers.
Turn it back on and measure the DC offsets. Anything over 50 mV is broken. DO NOT CONNECT THE SPEAKERS IN THIS STATE!!!!!!!!
-Chris
Hi Ben,
I hear ya!
You really must figure out where your fault is. What is the voltage on the DC servo output? That's pin 6 on the op amp. If you aren't comfortable doing this, don't!
-Chris
I hear ya!
You really must figure out where your fault is. What is the voltage on the DC servo output? That's pin 6 on the op amp. If you aren't comfortable doing this, don't!
-Chris
13.85 and -12 I'm not sure which is pin 6
does it go 1-4 on one side then 5-8 on the other, or 1 3 5 7 and 2 4 6 8
Thanks Ben
-12 volts I checked the pinout of an ad711
does it go 1-4 on one side then 5-8 on the other, or 1 3 5 7 and 2 4 6 8
Thanks Ben
-12 volts I checked the pinout of an ad711
Hi Ben,
The dot is pin 1. The pins count around in order.
Actually, google the data sheet for an NE5534 or 741 dip. The pinout is the same.
-Chris
The dot is pin 1. The pins count around in order.
Actually, google the data sheet for an NE5534 or 741 dip. The pinout is the same.
-Chris
Hi Ben,
That is substandard. 😉 Houston, we have a problem.
Start by checking basic things like grounds. Check each diff pair transistor's base to RCA ground voltage. They should be equal for each pair.
Sometimes life sucks just a little ........
-Chris.
That is substandard. 😉 Houston, we have a problem.
Start by checking basic things like grounds. Check each diff pair transistor's base to RCA ground voltage. They should be equal for each pair.
Sometimes life sucks just a little ........
-Chris.
Hi Ben,
At this point you really ought to do some reading so you can understand how an amplifier works. I'll accept a very basic understanding. You need to know this stuff.
-Chris
Differential pair. Two transistors matched (hopefully) in gain that are mounted closely together (hopefully) and with their emitters tied together to a device that holds the total current essentially at one constant value. See also "long tailed pair".
At this point you really ought to do some reading so you can understand how an amplifier works. I'll accept a very basic understanding. You need to know this stuff.
-Chris
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