4 
3 iPhone 6S - Volume down button
Bought the phone that apparently had a problem with the volume buttons. Opened it and the water indicator from the logic board was red, although the one near the sim tray was white, so I assume partial water damage. I took it apart and washed the entire logic board with 99% isopropyl and installed a new upper component flex cable to replace the buttons. the problem is that after all, only the volume down button does not work, just like with the old flex cable, I don't understand why. The volume down button works randomly for some time and then I have to keep clicking it for a few seconds until it works and then stops working after a few minutes. Have also tried switching the button covers and don't know what else to do to fix this. Would appreciate any help.
Update (12/15/2017)
Here's a picture of the connector itself, looks pretty good to me, no signs of corrosion that I can see.
crwdns2934109:0crwdne2934109:0
40 
crwdns2944067:02crwdne2944067:0
I tried cleaning it again with 99% isopropyl and a brush and it worked very good after I reassemble everything and then stopped working..
crwdns2934271:0crwdnd2934271:0 kraki crwdne2934271:0
I follow exact same.. 99% isopropyl is not necessary use brush.. First you need to dissemble everything.. Then soak everything into 99% isopropyl.. Let it soak in about a day.. While waiting for it soaking.. Go to Online Shop and buy a new one.. The new phone works like charm..
crwdns2934271:0crwdnd2934271:0 ArmRole Sovii crwdne2934271:0