Chosen Solution
Got my thunderbolt display completely black, nothing shows up on screen, no sound from speaker, no iCam, and it won’t charge my Macbook Pro laptop either (the charging light is not on at all). Is there a way to diagnose which component failed, PSU, logic board or thunderbolt cable itself? Thanks for advise! Update (11/03/2021)
Hi Dan, here are the pictures I just took, the TB cable looks good physically. Unfortunately, I don’t have the separate TB a as available, but I can buy one if it is necessary. So, if I get the images showing up with the separate TB cable, does it mean the internal TB cable is bad? And if no images with that separate TB connected, which means the logic board is bad?
Well from your symptoms your power supply has failed. If you had a USB Mini Voltmeter you should see the 5volts on the USB ports which is likely not present here. Opening the display you could also test the voltages the 120 AC entering and the power feeds to the logic board and MagSafe cable. 27" Thunderbolt Display Power Supply - 250W, Apple P/N 661-6048
