GFA-565 monoblock amplifier restoration
Note: This issue also may similarly apply to the GFA-585
This information describes what two people have done to restore GFA-565 monoblock
amplifiers. A typical problem that happens over a decade or so of use with these
amplifiers is that some of the capacitors will leak electrolytic fluid onto the printed circuit
board that can create a large DC offset that potentially can damage speakers or the
amplifier.
The printed circuit boards are made of paper, not fiberglass, which tends to absorb the
leaky electrolytic material. The cleaning job requires soaking and washing of the printed
circuit board repeatedly as well as removal and replacement of some components to get
in to difficult areas. Our service technician says he uses dish soap and soaks the printed
circuit board (due to the paper), others report they use a variety of solvents. Also, suspect
capacitors that have caused the leaks or may leak in the future are to be replaced. DC
offset must be verified to be low (well under 100 millivolts).
GFA-565 #1 “seller of rebuilt amplifiers on eBay”
Wrote the following:
Fully re-built and tested, these amplifiers have had a complete teardown, re-component,
re-certification, style restoration and function perfectly.
Because of the highly specialized front end of these amplifiers, ALL 565's have the same
problems. Thinking of buying a used one that isn't fully rebuilt? Well, you WILL have
problems with it because EVERY Adcom 555II, 565 and 585 suffers from the same type
of problem. And that usually shows up as blown fuses and a burnt speaker on one
channel-why take a chance?
The ONLY way to insure longevity in these amplifiers is to:
1) Completely remove all components from the circuit board, wash both sides of the
board with alcohol and acetone.
2) Install all new parts including, matched low noise metal film resistors, new capacitors,
new transistors, custom gain and noise matched transistors for the front end and then
set up to specs.
3) And just for the heck of it, I install genuine Solen Chateuroux capacitors in the front
end, replace the input wires with one strand of 30 gauge long crystal, 99.995% oxygen
free pure annealed copper, and I installed brand new RCA jacks.
• As you can see by the before shots, these amps were in a dusty environment.
• All the output transistors are the original factory certified matched sets.
• They have been pulled and tested on the curve tracer and exhibit no leakage.
• The mains capacitors have been pulled and ripple tested and are fine.
• The transformers have been ring tested for abnormalities and are OK.
These amps function perfectly and perform to ADCOM specs. A lot of time and care
went into these 565's. Why? Because I love what I do and I like Adcom products.
I have been repairing Adcom since the GFA-1 and have been a fan of their designs for 20
years. Why buy an Adcom that has one foot in the grave? These are completely rebuilt
and tested.
GFA-565 #2 “do it yourself”
Comment to customer:
Obviously your GFA-565 has an issue with DC offset. I have seen GFA-565s have a
capacitor leak on to the printed circuit board, causing this DC offset. It is a time intensive
process to remove and clean the pc board of this debris and is typically performed only
by a qualified service technician.
Response back
:
I fixed my amp based on your comments. I had a leaking capacitor just like you said. I
cleaned the board and replaced. There was also a transistor that the leads were loose in
the board (cold solder joints). One or the other or both must have been contributing to my
problems. I get a reading of .07 volts at the output now. I know you have recommended I
take it to a reputable dealer, but I thought I'd give it a go myself first. I design and build
custom circuit boards as a small part of my job, so I am somewhat qualified.
Attached is the board before I repaired it.
Here is a picture that shows the effects of the leaky electrolytic capacitors on the paper
(not fiberglass) printed circuit boards-
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