A1267 ACD 24" backlight issue
About two years ago I was playing a video game on my Mac Pro, although it was a low-end GPU, I was rendering the game on high graphical settings. The fans in the processor started revving up and making frighteningly loud noises. Then without warning the screen just shut off. From that moment I found that the display would not work unless I reduced the brightness below 10/15 increments. This got worse over time and now it only works on the lowest brightness setting. Shining a flashlight at the LED screen reveals a faint image when the display goes black. This suggests that the backlight is the issue. I carefully removed the glass, LCD screen and had a look at all the components inside. I'm no electrical engineer, but the Power Supply board and Logic board look fine to me (no swollen caps or burnt areas). I tested the voltage on the test points on the Logic board and it all reports fine.
From here, I don't know how to proceed troubleshooting this problem. It's always evading my attempt to fix it. The best way to troubleshoot this problem would be to temporarily swap identical model components to isolate what is the source of the problem. But I'm living in an area where nobody has a ACD. I've tried bartering with ACD sellers on online marketplaces to no luck. There are six main physical components inside the monitor that are culprits, replacing each on the off-chance would cost a collective ~€300 if I was unlucky.
I've read the service manual carefully several times but I can find no solution and I've read every answer to the backlight issue on fixit but find no solution.
I've taken apart and reassembled every component inside the monitor with the exception of the main driver cable leading directly into the monitor. It was covered with weird silver tape (electrical tape?) that had to be peeled back. But I haven't had the guts to attempt to remove the cable from the slot, as it doesn't seem to want to come out. Does anyone know how to remove this cable?
I have an update 13 months since my last post. The brightness in my display eventually gave out entirely and just didn't boot up at all when I powered on the processor. But then to my surprise the processor also stopped booting! Which implies the problem was with the processor all along.
Anyway, I bought a replacement graphics card and PSU individually, and neither part solved the issue. I cleaned the inside thoroughly and made sure everything is connected and such.
I am not done with the problem. I have not yet found a solution. My current focus is on the backplane board as I have ruled out almost everything else.
Occasionally the processor boots after an attempt to power up, with the display flickering for a moment and then going black.