# Adcom 5275 needs repair



## Dawgless (Oct 6, 2014)

Hey all! 

Just to be clear, I purchased this amplifier with the direct knowledge that it would need to be repaired before it would work. Either I just spent money on a nice piece of industrial art, or it might be something that can be repaired. 

I'm not an electrical engineer, even though I started out in college to become one... I guess I should have stuck with it now, huh? 

At any rate, here are some pics that I'd like the forum to take a look at to see if they think it can be repaired. I was told by the seller that it powered on, but didn't play sound. I don't currently have a test bed in order to power it up to attempt to get sound/voltage from the speaker outlets, but I figured I'd take the seller at his word. 

At any rate, here goes:




This one shows what the backing plate looks like. 

This shows on the top side of the PCB that there's no burning to the upper side.


I did test across the lifted section of solder that there is continuity between the contacts on it. Additionally, there was continuity between that and the negative terminal of the amp. 

Are there any easy tests I can perform to the amp to get a better understanding of what might need repaired? I see that there are some folks on here that might know who I can send it to to have it repaired. Anyone have any valuable input that would help me get this old amp back up and running again? My goal is to use this in my car, rather than try to turn around and sell it. 

Thanks!


----------



## ATOMICTECH62 (Jan 24, 2009)

The traces in question are going from the switching Mosfets to the primary windings on the transformer.Those traces pass the full load of the amp under high current drain.Since I have never seen this in an Adcom before it tells me this amp has been driven hard under low impedance loads.
However,even though it looks really bad its not something that is very hard to rework.I usually scrape the coating off the traces then lay desoldering wick on them and fill it all in with solder.This will pass much more current then the original traces alone.
But it appears that someone has done somewhat of a repair that should be sufficient to at least test the amp under low power for now.
There are 4 Mosfets for the transformer.2 for each phase.Then there are 2 rectifiers that have the same case style that are attached to the heat sink directly below the fan.Those will feed DC voltage to the 4 large brown capacitors.Using a DMM test the voltage across those caps with the amp powered up.You should get about +/- 25-35 volts DC from one side to ground and 50-70 volts DC across both +/-.Depending on you your 12vdc source.
If you dont get the voltage the odds are the Mosfets are bad along with the SG3525 PWM IC.


----------



## soccerguru607 (Nov 4, 2009)

OOPS...Guess this is not a Virgin...


----------



## Dawgless (Oct 6, 2014)

Thanks for the info Atomictech62! 

Also, I should mention, but I am using this website to arm me with information: http://www.bcae1.com/repairbasicsforbcae1/repairbasics.htm

My testing setup is going to be ungodly basic. More than likely, my 12 vdc source will just be a spare battery I have laying around, charged, and hooked up to the amplifier with fuse protection in place. 

I will say something weird happened last night when using my DMM, switched to resistance setting, that I was getting some weird results. When running ground side of harness from DMM and power side to each speaker terminal, on three of the channels, I received an open circuit reading, but on one, and I think it was the first one in, I received a resistance reading that was actually advancing(number getting larger). I removed the DMM terminals and replaced them, only to find that the readings were continuing to climb(guessing working towards an open circuit?). 

I have a bit more time tonight to do some testing. I'll see what I come up with and report back. 

Oh, and yeah, not a virgin amp, but I bought it knowing it wasn't! No complaints from me! Besides, gives me a project to work on.


----------



## Dawgless (Oct 6, 2014)

Okay, so I powered up the amp tonight and did some testing. I tested both of the SG3525AN PWM's and here are the readings that I received. All based upon a 12vdc input from a car battery. 

The first PWM I tested is actually under the black wires in this photo:

Readings as follows:
1: 0.00
2: 5.09
3: .54
4: .64
5: 2.00
6: 3.61
7: 1.90
8: 4.84
9: 5.72
10: .23
11: 3.96
12: 0.00
13: 10.42
14: 3.96
15: 10.57
16: 5.09

The secondary(what I call secondary) PWM tested is the one on the far left:

Readings are as follows:
1: 0.00
2: 5.08
3: .01
4: .54
5: 2.12
6: 3.60
7: 2.02
8: 4.82
9: 5.70
10: .23
11: 4.57
12: 0.00
13: 10.71
14: 4.56
15: 10.71
16: 5.08

I felt all of the FET's during the testing phase and there was one that got noticeably hot. That was the one nearest to the secondary PWM tested. I did have a speaker hooked up to the amp and as I was removing the speaker wire with power connected to the amp, I got some scratching noise, but there was no audible music playing. The fan worked. Another interesting note is that two of the four LED's on the board were slightly dimmer than the other two. As I moved the speaker wire around, these dimmer LED's would get slightly brighter. There is a red LED on the board and it was not lit. The dimmer LED's were on the audio side. 

Of the four black caps, I received no voltage from one side to chassis ground on any of them. When reading across each cap, one read no voltage, two read 30v, and one read 14v. Guessing all these caps are bad. All blue caps registered 11.7v when tested with the ground on chassis. 

I did test all the FET's on the power side and audio side. I got some strange readings and will have to draw up a sheet showing results of the testing. I'm also going to consult their datasheets to see what I'm supposed to be seeing. I received a lot of short circuits and also some open circuits.


----------

