Originally Posted by calimark
Two photos from the bad board...the other shows what normal PCB would look like.
The green is what appears to be copper oxidation- I need to look close under a scope, but my camera picked up what appears to be little bubbles around it.
I sprayed the board down today and now I can also feel a residue.
I wished I had not done that so I could have someone check to see if there was any conformal coating on the board.
Unfortunately, I have closed up the fixed receiver. Would have been nice to look at it in detial, but I will say, the board I put in there, came out of a more recent serial #.
I've been reading this thread, on and off, since Nov. 2011. I saw some of the early solutions and decided to chance buying a TX-NR708 (Like New Open Box) from Amazon Warehouse Deals for $242.95, knowing that no warranty was involved.
After several months it started to turn on by itself, mode cycling, and so on.
Upon disassembly, I never saw anything remotely resembling a gooey or sticky conformal coating on either the display board or the other (Logic Board?) so I just cleaned the board connectors and replaced the 40 pin IDE cable.
Not wanting to waste my time replacing my "Trusty" TX-SR706 back in my system again, I left it plugged in on Standby. I made sure it wasn't even in the same room as my main system as not to get a stray IR turn-on signal. Within a day or so it had turned itself back on. The problem was not fixed and so its sat for the last 4 months.
Even though I'm certainly not any kind of electronics person, in looking at Calimark's board photos and recalling that others had suggested the problem was due to a poor job of washing and neutralizing the acids used during manufacture, it seems that Calimark's theory of shorting between the board layers (through the holes) is "Right on the Money".
I don't see any of the Green Copper Corrosion in mine, but still think the problem lies there.
The method I'm going to try is;
1) Remove the hard clear conformal coating with electronics cleaner.
2) Soak board in a Baking Soda/Distilled Water solution with gentle scrubbing.
3) Wash board in distilled water.
4) Clean board in Ultrasonic Cleaner with "Fresh" Baking Soda/Distilled Water solution.
5) Clean board in "Fresh" Distilled Water in the Ultrasonic Cleaner, Blow off excess, and let board dry thoroughly. Possibly in a low heat (125 F) oven
I really don't see how this can "damage" an unusable board. If this doesn't work' I think that I write this receiver off as JUNK.
My question for Calimark (or anyone else) is; Can you see anything wrong with attempting this method?
Also to remove the rear (Logic?) board, do you just undo the back panel "module" (rear 1/3 section) of the receiver? I remember seeing a photo of a TX-NR3007 (I think) with this module separated from the rest of the receiver.
Suggestions are welcome. Thanks Jack
Edit: I don't plan to use this procedure on the Display Board because of many mechanical switches and fluorescent display.
Also can anyone tell me or lead me in the direction of how to determine the "Build Date" from the Serial #? An old retired bar managers "Search Skills" seem to be somewhat lacking!