Well after battling my problems with this amp for a year now I am finally in the home stretch with this brain teaser. These are known to be hard to work on, and very dangerous, but I'm not too bright so... I decided to take it on myself(with some diyaudio forum help:)thanks H9).
The Old Adcom's (585's, and 565's)suffer from a bad run of Elna capacitors that leak electrolyte onto the circuit boards which causes noise, and DC offset. If used in this state you can damage your speakers, or your amp. To fix these you have to remove all the caps on the input board, and clean them with simple green mixed with water 10/1. Well I cleaned these suckers 3 times, and still had the DC offset problem. I just ran it anyways. With the number of drivers it was hooked up to I wasn't worried about damaging the speakers.
Well doing some experiments with different crossovers in my custom SDA's I accidentally shorted one of the channels. POOF! I blew a transistor in both channels. No big deal right. Wrong. You need to replace the whole set with beta matched transistors. OK now I need to purchase about 40 transistors to get 20 that would be close enough to use. I wanted to get the job done right. The Toshiba transistors that are used in the older Adcom's are no longer available. That bummed me out. I love the sound of the big GFA's. So I went on a hunt. Finally about 9 months later I found this guy on Ebay selling the transfo's I needed. The problem was he was selling 500
So I won 500 transistors. I could not for the life of me figure out how to beta match them. So I bought an old Heathkit 121 transistor tester for $60 on the bay. Now I have all the transfo's I need:D, and a tester. So I rebuild the outputs, and test it. No big surprise. 1vdc of dc offset:( THE ONLY WAY TO REMOVE THIS NASTY DIELECTRIC IS TO USE AN ULTRASONIC CLEANER!.
So now I have an ultra sonic cleaner:D I took the input boards back off the amp, and tested every resistor, and diode on that sucker. I also replaced the OP-Amp that sets the DC offset servo. For haha's I replaced a few of he voltage regulating transistors too. I found some bad diodes that were leaking back wards, and replaced them. Put everything back together, and fired her up.
It took a little while for her to settle down. Had some DC offset. I had to set the bias to 24mv a few times. After about 5 hours of breaking the "new amp in" she self corrected the DC offset to specs well within the acceptable range. I have DC offset from 0(yeah you read that right) to 10mv:D Well it's almost completely done! I have just a couple of caps that I am going to replace (105c) instead of the 80c caps I have in there now, and I am ready to button her up. I might install some beefier main caps, and I am definitely going to add some active cooling via 120cm 12v fans. I don't need much just some slow quiet fans. These Adcom's could literally cook an egg.
Thanks for reading. My shrink suggested I right right down trials that I have had in my life, and read them. Plus I just wanted to share my experience with you guys. your the best:)