ADCOM GFA-565s

[gbowling]

I have a pair of GFA-565s that are in fair condition. I want to get them up to date to make sure they don't have the "DC leakage" problem.

They do work, but also make noise when powered on.

I have considered doing the mods myself, and have reviewed several good threads here about doing them. However, I seem to have trouble finding the 100V 39,000 uf caps and really don't have the time anyway. The caps referenced in other threads are either no longer available or I can't seem to find them. Did I also mention that I really don't have time to do this anyway ('')

There are two companies I find that do mods for this amp.

Musical concepts
http://www.musicalconcepts.com/adcom.htm

and

MJR
http://www.mjraudio.com/services.php

Does anyone have experience with either of these companies doing mods/updates?

Also, the mods/updates are going to run $1000 or so (unless I do it myself) and I wonder if this is worth the money, or should I just sell them and buy a new amp?

[bbtwins]

Does anyone in Canada fix and do upgrades to 565's ?

[BTG]

Put a meter on the outputs and measure the DC offset. Shouldn't be more than 15mV if the servo is working. If it is high, probably has open 10ohm ground resistors or a bad servo IC.

If the amps work, use them and enjoy. They are great amps and dropping $1K is a waste IMO.

[gbowling]

Thanks BTG. Good points. I guess I was having a "lazy" moment during my original post.

It looks like the large capacitors (100v, 35000uF) aren't bad as best I can tell. They don't have any leakage that I can see and they seem to charge up, discharge correctly.

As for the DC Offset, one amp has 0.5 vdc across the outputs, the other has 3 vdc across the outputs.

Obviously the one has a big problem, the other one seems to need a bit of work as well.

I don't have a service manual, where do I find the ground resistor?

The servo IC appears to be on the input board and I've seen reference to replacing it with an OP97.

Any other pointers? There is a long thread on here from MJRaudio with a complete rebuild, but I don't believe mine require that.

They have used in a well ventilated A/C environment for many years. All the boards look fairly clean (except for dust!) and I don't really see many problems. Probably replacing the ground resistor and op amp is a good suggestion and may be all that is required.

Thanks

[Nordic]

I would try to find out the original bias levels and see if the channels can be dialed to this, then do the offset tests again...

Anyway 3V is not a "big" problem (though it may kill speakers), full rails on the output, now that is a big problem...