AP55c - took it apart to see what is wrong with it?

Question

My AP55c has been giving issues on the 5ghz band, so I decided to take it apart. 
 Yes, I checked it is out of warranty. 
 I found all these strange marks on the PCB that look like water stains. They could also be solder fume residue. There is a liquid on the heatsinks between the chips and the fixed pads, looks like some form of oil. 
 There appears to be corrosion around some of the joints. I can only think if they are water stains that they are condensation points. At times around here the humidity hits 80% inside, but why only the AP55c which sits on a stand in the middle of the room and why only the 5ghz channel is affected? Anyway it looks like I am up for a replacement whuch more than likely will be an AP55.

IanMorehouse · Accepted Answer

More experimentation today. The settings I identified above have no affect. 
 I installed a tp-link dual band usb wifi device, 2.4ghz quick connection and maintains connection. 5ghz starts and quickly disconnects. 
 Other little issue is I get better and more consistent throughput from an AP10 down the other end of the house, through two thick metal doors and a silvered mirror let alone lots of plaster. 
 So conclusion, this AP55c is dead and should be buried. 
 
 Update - having said that about throughput the AP55c 2.4ghz now connects at a reasonable speed 130-144mb/s.

Dlabun · Answer

That totally stinks the 5Ghz didn't come back to life. Odds are the 5Ghz radio was shorting out from the flux and the cumulative damage was too extensive. Hopefully Sophos takes a hard look at their quality control program and fixes these avoidable manufacturing issues.