Chosen Solution
The built-in keyboard on my 15” mid-2015 MacBook Pro is not functioning— the trackpad is working without a problem. I’ve tried replacing the trackpad flex ribbon cable between the logic board and the I/O controller. No luck. I don’t see any apparent damage and a wired or Bluetooth keyboard works just fine. Any help would be extremely appreciated. Part that I tried replacing: Touchpad Trackpad Flex Ribbon Cable Compatible for MacBook Pro Retina 15" A1398 APN: 923-00541PPN: 821-2652-05, 821-2652-A https://www.amazon.com/dp/B07GS1GXKG/ref… Update (05/09/2020) Well the connector and cable look fine so I went ahead and disassembled the logic board. When I flipped the logic board over, the backside of the keyboard connector socket seems to have some corrosion and maybe even a blown capacitor (or whatever that is). Take a look at the right side of the first two images below.
Not sure I follow why you replaced the TouchPad cable. This model uses a direct keyboard connector to the logic board. Review this guide MacBook Pro 15" Retina Display Mid 2015 Logic Board Replacement After disconnecting the battery, jump down to Step 33 & 34 Is the connection good? Is there any staining or corrosion around the connector? Update (05/09/2020) Looking at you new images you do have a damaged component! The Resistor R4821 (10K 5% 1/20W MF 201) appears damaged
Looking at your last pict there’s a broken trace on your flat cable that’s shorting the two other traces on the left. That short maybe the cause of the damaged resistor. You could repair that trace with a liquid conductive silver pen but before you have to carefully cut the folded trace with an exacto and scratch the continuation of the broken trace to see the coper trace and then apply the conductive silver to restaure continuity on this line. Other solution is to replace the keyboard.
