project corrosion

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so, i gambled on a cheap ADCOM 4302 off ebay a few weeks ago. after a long shipping fiasco, it finally showed up. good thing i didnt spend much on it, as it looks like it was stored outside for a few years. it has a serious corrosion issue. as evidenced here:

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and here:

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i found one transistor leg that is completely corroded through. also one cap lead popped right off as i was pulling caps because it was corroded so bad. the little wire that runs from the small turn-on sub board, to the main board was also corroded in half. it looked so bad i didnt even try to power it up. so, it may be a lost cause, but i think i am going to attemp to get it going. if for nothing else, to practice my solder skills. i dont see any evidence of the amp ever failing before. so i may be able to just swap some parts. reflow a whole bunch of stuff, and get it running. the fan circuit has been modified, but i have seen several different variations of that from the factory. this mod is a little different as there is a resistor that was clipped off the board. but i am willing to bet it will still work. i have pulled all the caps, and the toroid so far. i even managed to get the snap-ins out without pulling any vias, or lifting any pads (huge accomplishment for me! LOL)

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i have a friend that has been teaching me how to do this kind of work for a few years now. without his shared knowledge i would probably throw this amp away. but it should be a fun little project. and if it doesnt work, oh well, i will only be out a few bucks, and i will have gotten some good practice in. but, i have a few questions. i am needing to pull the heatsink to properly clean the board so i can see what i am "really" up against. but i dont know how to handle the thermistors:

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should i pop them free from the heat-sink? or desolder them from the board and leave them affixed to the heat-sink? what is the goop that they use to affix them? not sure how to handle those little guys.
also, anything else not-so-obvious i should scrutinize because of this amps obviously "moist" past?
and, i am thinking (per reccomendation) denatured alcohol, and a bristle brush for cleaning. any other reccomendations?
BIG thanks to anybody who wants to chime in!
 
If the material that's binding the thermistors to the heatsink is hard, it's likely a thermally conductive epoxy. If it's soft, it's likely silicone. I'd desolder them from the board.

When an amp gets wet, there is often a lot of damage to the vias and the connection between the top and the bottom of the board is lost or becomes intermittent. I'd suggest examining all of the vias that do not have a terminal lead through them with a lighted magnifying glass to see if any are damaged.

Sometimes, the pads won't take solder well. A fiberglass scratch brush (ebay) works very well to clean the pads and will allow solder to flow much better when they need to have solder applied.
 
thank you kindly for the input Perry! i will scrutinize the board thoroughly. through the learning process, i have damaged my fair share of boards. and also learned the proper techniques to repair damaged boards LOL. and, thanks for the tip on the brushes. i will pick-up a couple of those and attack this thing and see if i can clean it up. getting the toroid out was much easier than i thought it would be. but i am not looking forward to pulling the op-amps. i might just have to leave that one to my buddy with proper tools, and experience. thanks again!
 
These brushes produce small glass fibers that can be irritating. After cleaning the pads, clean the fibers with cotton swabs and solvent (alcohol or acetone). Do not blow them off with compressed air.

I don't think this amp uses any op-amps (but I could be wrong). If you're referring to the power supply driver IC, cut the leads from the IC as close to the body of the IC as possible. Add new solder to the top of the board. Heat the solder on the top of the board and remove the pins, one at a time. This will virtually eliminate the chance of damaging the board.
 
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