Question about Adcom GFA-5802 2-Channel Amplifier

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ADCOM GFA 5802 POWER AMP NO SOUND, BUT POWERS UP.

Hello problem solver!
I own a adcom gfa 5802 2 channel power amp (Home audio). I bought it off a friend who did not want to spend the money to fix it. I'm pretty good with a DMM and a soldering iron. I did a couple of checks but nothing came up conclusive. Any idea where i should be checking for these issues?

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  • damonrink
    damonrink Nov 12, 2008

    Hey guy, thanks for getting back to me so quickly! On the amp output board there are 32 output transistors! 16 for each side. Do you want me to take out just one and measure the voltage or what?

  • damonrink
    damonrink Nov 13, 2008

    I'm not quite sure what you mean by lifting the base of each transistor. I have to de-solder and check right or can i check it in circuit. By the way, my meter is a Fluke 179 true rms. Do i use the Diode check setting when checking it in circuit? Also, do i have it powered up when checking?

    I did order a schematic for this particular Adcom amp, should be here in a couple of days. You mentioned that all 8 transistors were in paralell, did you mean 16? There are 16 per side! Its the largest Adcom makes 300 watts per channel! Here are some pics of the internals. Well, scratch that. My pics are two big and i do not know how to reduce them. If you have an email address that i can send you the pics, that would be great.

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It was funny to read this post because this amp has MOSFET output transistors, so there is no BASE and it is difficult to test them by the meter. Also the amp has huge power capacitors @+-80 volts rail and any experiment like "lifting the base" could cost you burned board or $250 in parts per channel. I think the best way is to bring it to an repair shop.

Posted on Feb 24, 2009

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Remove the output transistors and measure each of the sets of 3 pads and report the voltage readings here. I suspect that you have either a blown driver circuit or output transistors. The voltage readings will give me an idea on where to start looking for specifics.

Thanks,
Dan

Posted on Nov 12, 2008

  • ABRsvcs Nov 12, 2008

    Unfortunately, all 8 are in parallel. One being bad will kill the whole side. Also, it is good practice to replace any transistors that are in parallel as well as their compliments any time that a channel gets smoked. It may appear to be an expense, but when 1 shorts, it places stress on the remaining ones. That stress MAY reduce the lifetime of that transistor. Basically it comes down to this: Change the entire side of the transistors while you are in there and you will get longer life out of that side. Otherwise, expect to perform the same repair only on another transistor soon.



    In order to save a bit of time, try lifting the base of each transistor. (That should be the one with the B+/B- voltage on it) and post the readings of the remaining pads here.



    Thanks,

    Dan

  • ABRsvcs Nov 13, 2008

    Ok. I wasn't clear. Of the 16 per side, each set of 8 are in parallel. The two sets are compliments of each other for each side. Lift the base connection by unsoldering it on each of the 32 transistors. This will allow the voltages to be read with the unit powered up without drawing any current (main B+/B- not available through the transistor base). In this case, one of the 2 remaining pads for each compliment should be the bias voltage (either 0.6 or 1.1V) and the other should be 0. The 0 should also be the speaker line.



    With the unit on, measure each pad to ground using your DC meter and post the voltages here.



    Dan

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Try to do it with this manual if you can handle it



ADCOM GFA 5802 SCH Service Manual free download schematics eeprom repair...

Posted on Mar 18, 2016

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Have you check the fuses? if blown you need the check the amplifier for damage parts

Posted on Mar 12, 2016

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