Q: PowerMac G4 won't turn on with Cinema HD Display connected.
Hi. I have an odd problem. My Mac has started acting up with my 23" Cinema HD Display, which I got ages ago for use with my PowerMac G4 (connected via ADC). I started having problems with the monitor turning off randomly and the only way I could get it to come back on was a combination of faffing around pulling the plug out and putting it back in turning the Mac on/off. However one day it went off and no amount of fiddling around seemed to be able to get it to come back on (the monitor that is, the Mac was still running apparently fine). I assumed the monitor was dead so I managed to source another identical 23" CHDD that was supposedly working fine really cheap. However with that "new" monitor plugged in, the Mac refuses to power on at all (with the other monitor it would turn on but the monitor would just stay dead).
I eventually found that I could turn the Mac on if the monitor was unplugged but plugging it in while the Mac was switched on would cause it to pretty much immediately turn itself off. Then I found that if I unplug the Mac, and the monitor, plug the Mac back into power and then plug the monitor in, the Mac turns itself on, there's long loud beep, the CPU fan spins up rapidly and then slows down again to normal levels and the Mac boots to Open Firmware, after which I can have it boot to OS X and start using it normally.
It continues to work this way until I shut the Mac down. Then it starts refusing to turn back on again. I can however instead put the Mac to sleep while it's on, it will go to sleep and the power lights start to glow, then I can wake it up normally and it continues to work fine. The only odd thing at this point is the power lights on both the monitor and the Mac continue to glow as if the system is asleep, even though it's awake and apparently running fine.
Any ideas what's going on here? I've tried testing the backup battery, it seems Ok at 3.7v. Resetting the NVRAM, and trying a PMU reset by pressing the button on the logicboard didn't fix anything either. I even tried using a different graphics card and the problem is exactly the same.
PowerMac, Mac OS X (10.5.8), null
Posted on May 28, 2016 7:10 AM