I'm trying to diagnose an issue with a Mac Pro Early 2008. When I received it, it just doesn't boot: when I pushed the power button, it started for less than a second, and then it automatically shutted down. No chime, no gray screen, no apple logo.
I opened it, removed one of the memory risers, and kept pressed the diagnostic button when I started it. After doing it, the Mac booted properly. When I reinserted the memory raiser, it just won't boot, but the power led stays on anyway (not shutting down after 2 secs)
So, I returned the mac to the owner and it worked by one day. At the next day he had the same trouble. I instructed him to open the case, press the Diag button, and it just started again.
But, I have a few questions: is this related to the SMC? As i seen before, letting the computer unplugged for 15 seconds is "enough" to reset the SMC, and Mac Pro, from Early 2008 doesn't have a SMC_RST button. What I'm doing when I press the Diagnostic button then? Why it boots when I do that?
And, on the other hand, where can I find a place to interpret what diagnostic leds are telling me.