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Old 4th June 2006, 01:18 PM   #1
Wyseman is offline Wyseman  Italy
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Default Adcom Gfa-585 not working properly!!!!PLEASE HELP!

Hello everybody, i'm from Italy, and this is my first post here. First of all sorry for my english.
I'm proud to write for the first time in this forum, full of competent people, wich has been so useful to me in many occasions.

Now, this is my problem: when i turn the amp on, the two leds of the thermal protection turns on too, and a strange cracking rumor came out from the left speaker. The rumor is variable and lasts for 2 or 3 minutes, slowly decreasing an popping. Also the left led lit accordingly to the rumors, and the right channel led is also lit, but without rumors coming out from the speaker. Also when i turn on the amp i hear i strong pop from the left speaker and not from the right one.
I'm a newbie, not very capable in electronics, but able to use a tester and a solder, i will like any advice, or if someone would like to spend his time i will appreciate some sort of step by step guide by this post.
I checked the caps reading from a post here and tey seems to be in good condition, with no liquid leakage.
Also the left woofer came out a bit when the amp is on.
Please help me!!!!! Thank you all!


P.S. for any purpose my system is: sony 556es cd player, mirage M3 loudspeakers, museatex analog control center preamp and the self destructing adcom
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Old 5th June 2006, 12:35 AM   #2
clem_o is offline clem_o  Philippines
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Hi!

DC offset with rumbling and crackling could mean bad electrolytic capacitors, (sometimes you cannot see any leaks), bad transistors (usually the input stage(s)), or faulty solder joints.

Remove your speaker load and plug in your tester into the left channel (set it to read DC volts). You should be able to read the offset voltage (that's causing your speaker to 'plop'. Does the offset voltage go down after a few minutes? If yes:

Let the amp cool off, borrow your wife's hair dryer and gently start heating the parts one section at a time, see if you can isolate the general area which is sensitive to heat...

If you suspect faulty solder joints, you can bring out the magnifying glass and look very very well at the underside of the pcb; resoldering all the parts isn't hard to do actually if you are willing.

Cheers!!
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Old 5th June 2006, 02:02 AM   #3
Wyseman is offline Wyseman  Italy
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thank you very much clem_o, tomorrow i will try the things you told me an i will post the results! Thanks!
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Old 5th June 2006, 02:08 AM   #4
anatech is offline anatech  Canada
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Hi Wyseman,
These amps are not normally too hard for an experienced technician to service, but is a little too hard for the average hobbyist. There are some special parts used.

One thing to check is a 100 ohm resistor from signal ground to supply ground on the input pcb. They can go open and cause DC offset. They will only go open if you have more serious problems with your system.

Anything more than that and you should be looking for a warranty service center (one that used to work on those new). I have been seeing some amps serviced very poorly as of late.

-Chris
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Old 5th June 2006, 02:29 AM   #5
clem_o is offline clem_o  Philippines
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Hi Wyseman,

Good luck! You should listen very well to what anatech (Chris) says - he's serviced many Adcoms...

Cheers!

Chris, just sent you an e-mail...

:-)
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Old 5th June 2006, 04:51 AM   #6
Wyseman is offline Wyseman  Italy
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thank you anatech, i will check, the fact is that here in Italy adcom is no more distributed, and the only "serious technician" near here asked me 350E for a complete check of the am, bu i payed it 400E, so i would try myself with the help of a friend of mine who is an electronic engineer. clem_o, i did't receive any email, my other email is wyseman@tele2.it

Also, is there somebody ho have the schematics in good quality for this amp? I foun something in another ol post but they are low quality, i can't read almost nothing!

Anyway, thak you so much for your help, i will post what happened tomorrow.

P.S. Is there somebody who knows about SENTEC ACM1 A? I think i will open another thread about it, i buyed those two monos in ebay, and they are sweeeeeeet and completely grainyless i didn't expected!
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Old 5th June 2006, 03:43 PM   #7
Wyseman is offline Wyseman  Italy
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Ok, today i put the caps back in place.....and the main fuse blowed! Sigh! I will check everything again end then post something!
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Old 5th June 2006, 03:59 PM   #8
anatech is offline anatech  Canada
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Hi Wyseman,
Sorry to hear that. Simple would have been good.

1.) So, unplug it and discharge the filter caps.
2.) Measure from each channel output to each cap supply terminal.
3.) Let us know what you find. Make sure the fuses are good.

What I do not want to see is you increasing the repair cost. That does not help your cause in the least. No matter how much it cost you to buy, it will cost some amount of money to repair. The two are unrelated. The very least expensive repair is the one that is properly done. That means matched output transistors if they are gone, a complete new set (for the blown channel). Anything else is a "hack" job. Don't waste your time and money on that kind of work.

Matched transistors means that you buy a bunch and measure them, you use the set of ones that the hFE matches. Match the NPN set and match the PNP set. I don't expect you to be able to match the NPN's with the PNP's (it would be nice ). Not likely.

-Chris ( Clem, got it thanks. Replied)
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Old 6th June 2006, 01:55 AM   #9
Wyseman is offline Wyseman  Italy
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Hello, today i tried again, but the main fuse keeps blowing! Sorry anatech, i didn't understand you, tou mean connecting the tester on the amp output and on the cable left free by the cap?
Anyway, my friend (the engineer) tested my caps and told me that one of them is completely dead!!! Could this be the problem? Thanks!!
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Old 6th June 2006, 01:55 AM   #10
Wyseman is offline Wyseman  Italy
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Just some things Chris, first ao all thank to you and clem, second, i read in other posts that you were an adcom technician 8or something like that) and i want to ask you if you know some ways to improve the 585 now yhat it's open....if there's smething to change with better components or anything else.for the main problem, i think i will go for the repair center, probably the caps are the problem but i don't want to risk!
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