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Old 11th June 2011, 10:37 PM   #1
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Default Noob here. GFA565 running hot.

Here's my original post:

Hello.
I've spent hours reading the threads on this forum about the Adcom GFA 565's. I have two of these monsters. One has never given me any trouble. The other I've had repaired twice at over $250 a pop. The first repair was a 10K ohm 1/2 watt resistor, a 47 Ohm 1/2 watt resistor and a 2.7 Ohm 1/2 watt resistor. Parts $23 and $230 labor. The next repair on the same amp was part number 2SC945 transistor and 1 ohm 1/2 watt resistor. $18 in parts and $281 in labor. This done by an Adcom certified repair store.

It started both times with distorted audio. I know it's vague but I'd love to learn how to fix this myself in the future. If this sucker breaks again I'm going to either fix it myself or use it for a boat anchor.

Any idea what they "fixed"? Is it just because the amp is old?

BTW, serial number is 011214627

Thanks in advance. I'll keep reading and learning in the meantime. I really need to find the repair/service manual for these things.


Well, I had it repaired for another $200. After a 8 months it's doing it again. Distorted audio after an hour or so of running. Runs pretty hot.

With my meter on the DCV 200m setting, the DC offset starts fluctuates between 11.8 to 14.8 then comes down to fluctuate between +03.2 to -05.0 mostly hovering around +03.1 to -03.2. with occasional excersions beyond + or - 04.0. Just saw one go to -40.0

Amp is warm to the touch, but not hot. A faint buzzing can be heard from the board in the back. The two little heat sinks on that board are very hot. Can't see any evidence of leaking caps on the top and the size of those big caps makes me nervous to go deeper.

I've seen that anatech seems to be the go to person. Any thoughts? I love these amps but have no more confidence in the local repair shops.

Thank you!!!!!
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Old 12th June 2011, 12:03 AM   #2
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Thanks for sharing. I can't help but am interested because I run 5 GFA555IIs in a 7.1 system.

Which Adcom certified repair shop did you use?
Same shop each time?

I have a schematic for the 555. Let me know if you want it.

Here is a link that you may want to look at.
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Old 12th June 2011, 03:44 AM   #3
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Those are fine amps. I have the schematics for the 565. Email me.
As far as the big cans, apex jr has those if you need to replace them. 35,000Uf 120Vdc Computer Grade Caps
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Old 12th June 2011, 04:17 PM   #4
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I used Normans Electronics both times. They used to be Adcom approved.
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Old 12th June 2011, 05:44 PM   #5
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Edit: The amp gets hot on with no signal as well. Just plugged in and on with no input or speakers connected.
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Old 12th June 2011, 09:50 PM   #6
anatech is offline anatech  Canada
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Hi gt4rcdude,
Warranty service work never did address this fault. It showed up after many years in service, so no one knew what was going to be a problem. In this case, your best service shop is going to be one with really good audio technicians on staff. A shop or technician that was previously authorized for Adcom is a bonus. Then that person will know all the other ins and outs of these amplifiers. The people you used, or at least that technician, isn't a great service tech. Probably an okay one that is neat in his or her work (I hope - did you look?) and that's all. However, compared to the average service technician, better. You need to remove the top cover and actually look at the areas they serviced. Those areas should be clean and neat. If not, my estimation of the quality of their work just slid down a whole bunch of notches.

Why clean? Because this is the only way that a person can inspect their own workmanship once they are done. Flux will hide bad solder joints, even unsoldered connections! Flux can also easily hide solder bridges and cracked foils. I've even seen a solder ball on a lead buried by flux ... and no more solder pad!! It's pretty clear that person did not even check their work, but the service bill indicated that the bias currents were set and DC offset checked. How?

The normal state for any amplifier just turned on and not driving a load is to warm up to some level dictated by how much power they dissipate due to bias current. So amplifiers like these will run warm, but not hot. Now, the bias current will not change suddenly unless the amp breaks into oscillation. So your measurements have me worried.

The amplifier was never repaired in the first place. So any money spent on repairs was a waste (sorry about that). It's not the fault of the amplifier, so you can't justify dumping it or subjecting it to service that is substandard. It's just a thing that has never received the attention it needs, that's all. I do understand where you're coming from though. At this point in time, you should be speaking with the shop owner for money back since it is pretty clear they did not fix the amp on any occasion. A 90 day warranty (industry standard) on service does not excuse the extra charges. Now you will see their true colours. You should either be refunded some, or they should refund some and fix the amp properly. Nothing here is your fault. I would expect the reasonable service charge to exceed the $250 you paid the first time in all fairness though. These can be pretty ugly, although I've repaired some that went with no problems before.

These amps were built with some defective capacitors that leak electrolyte. This stuff is invisible under normal light, and corrosive as all heck. Removing it is arduous work, but it can be done. In a really bad case, I have had to strip one board down completely and I'm almost ready to put it back together again. I've had it for a long, long time, but I can't return it in the state it's in. The amount of scrubbing I've done is amazing, but I think I finally got the stinker! It's probably one slightly conductive path that is giving me grief. Oh, and the parts in the area need to be cleaned or replaced as well. You can't just clean the PCB and expect it to be okay.

So I'll repeat, inspect the areas were they have claimed to have done work. The work done should be neat and tidy on both sides of the PCB.

-Chris
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"Just because you can, doesn't mean you should" my Wife
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Old 15th June 2011, 02:42 PM   #7
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Thanks Chris,
I unscrewed the PCB and was able to flip it over. Looks like some scraping was done on the board. Doesn't look like any caps were replaced though. The boards themselves are in very good shape. No rot, corrosion or damage. I'm just frustrated because I have no where to turn. Normans Electronics is the oldest, most reputable shop in Atlanta. Not a cheap, fly by night outfit. I just want my babies fixed once and for all.
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Old 17th June 2011, 03:05 AM   #8
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I'm going to weigh in here a little bit. I have done quite a few 565's and the symptoms you give sound very much like the remnants of a leaky cap repair job.

I say remnants, because when the caps leak, the electrolyte gets right into the cheap-assed pressed paper circuit boards. If they were nice green fiberglass there wouldn't be a problem. When the electrolyte gets into the board, it forms very hiZ current pathways that play havoc with the front end.

What I have done with excellent success....but it a LOT of work, is to completely strip the board, and scrub it with alcohol and a circuit board brush, then rinse it with alcohol. When it dries ( I leave it for a day ) do it again, and repeat the procedure one more time after that.

Then do the same to the components, or do a wholesale replacement.

That is a sure fire guaranteed cure for the wandering offset problem if the components are known good.

Haven't had one come back yet once new caps were installed !

Rob
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Old 20th June 2011, 03:37 AM   #9
Apex Jr is offline Apex Jr  United States
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Quote:
Originally Posted by wannabeaudiophile View Post
Those are fine amps. I have the schematics for the 565. Email me.
As far as the big cans, apex jr has those if you need to replace them. 35,000Uf 120Vdc Computer Grade Caps


I also stock Adcom 22,000Uf 100V for $23.95ea
http://www.apexjr.com/images/AdcomCap.jpg

Steve @ Apex Jr.
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