I have the same problem (iOS 9.3.5), after I replaced the battery and the Display. I recognized, that Siri and videos recorded by the front facing camera don't have sound, just static. On another iPhone 5 (iOS 10.3.3) it is working fine, so it seems that the "Front-Facing Camera and Sensor Cable" is not the cause. May be I damaged surrounding components, when disconnecting the Sensor Cable off the logic board :( Everything else is working fine.
This mode is called "download mode", I think You can set it to factory settings by flashing it over odin or heimdall. XDA Developers will have some guides.
Last saturday (december 5) it began to be grayed out again, for some hours. After a few hours it was working again. Since wednesday (december 9) it is grayed out. Any suggestion?
It worked for me for a couple of weeks, between 2 and 3 months. I reflowed the chip with 200 c like in step 25. Should I try to reflow the chip with more heat (250-285 c) like in the picture?
