About 6 months ago my Mac started randomly shutting down / not starting up. Pulling the power cord usually did the trick but things got progressively worse. Then on startup there would be no chime, no screen but the power light would blink. The potential issues were numerous and I slowly worked through them. I swapped out the backplane board ay one stage and still had the exact same issues. Eventually it just stopped working. Currently I am referring to the Apple Technician Guide and doing minimum configuration testing (with mixed results). I have stripped out the drives, graphics card, processor tray / cage, blue tooth, wifi, battery, front panel board. I have been through this at least process 4 times. LEDs for OVTMP CPUA and OVTMP CPUB always flash when tested (with PSU and backplane installed) and the 5V STBY LED always flashes when the DIAG button is pressed (power and backplane would appear okay). Once I install the processor cage (but not the tray) I should be able to jump the SYS_PWR solder pads. Usually this is where I get a failure and cannot progress (and there is no direction from the Technician Guide what to do if you fail at this step). Having said that, I did get a jump start last night and got the processor tray in with RAM (fans spinning). Then when I restarted this morning (same config) no luck. And today I can’t jump SYS_PWR pads with just the cage in (no tray). I’m getting pretty frustrated to say the least. Does anyone know what I could try or have been through a similar experience?