Troubleshooting No Video On A Power Mac G5
I got a call today from someone who was in need of help with their Power Mac G5 computer. The problem they were having was the system would power up, the famous startup chime sound effect would play but there would be no video displayed on the monitor. As far as the monitor was concerned the computer was still off as the power light on it would remain amber instead of turn green. Unfortunately you don’t get Mac-oriented training in most technical institutes so I didn’t know exactly how to approach the problem. Is it hardware? Is it software? It was time to call for reinforcements!
With the help of a friend of mine who happens to use a G5 for graphics design work on a daily basis we began troubleshooting this machine. Going off of Apple’s official troubleshooting pages we tried holding Command-Apple-P-R at boot in an attempt to reset the PRAM (which is similar to a PC’s CMOS) but for some reason it would never reset, or at least we never heard the second chime sound indicating a reset.
Ultimately the thing that did the trick was unplugging the systems power cord, opening the case up, removing the dual-fan assembly that’s in front of the RAM slots and pressing the PMU Reset button located on the “logic board” ONCE! The ONCE part of this was stressed as pressing it more than once could potentially turn the system a trendy looking boat anchor.
When the system was powered back up there was no video for a moment and then the OS finally started to boot. I shut the system down, turned it back on and it still worked. So I had considered this a finished job and decided to shutdown and take the computer back to it’s owner. Well, then things got strange all over again.
With the system back under the desk in its original location, reconnecting the USB cables for the printer, keyboard and mouse to the computer and pressing the power button I was greeted to a chime, the grey-on-grey Apple boot-splash screen but that was it. No whirly-circle busy animation, no hard drive activity, nothing. So I forced the power off and waited before retrying again. Suddenly we were back to square one with no video on screen.
I decided to see if hitting the PMU reset would help here so I unplugged the system, opened the case, pressed the button and shut it back up. That didn’t work. Finally I unplugged everything from the system except the keyboard and the power and turned it on again. The system finally booted up to the desktop. I shut it down and reattached the printer and the networking cable while the system was powered off. For some reason this had an effect on the computers ability to boot up because it didn’t want to show video once again. I pulled everything but the keyboard one more time, powered it up and it booted all the way up once more. While the computer was on I reattached all the USB cables as they were, which produced no problems, shut the computer down, and finally upon powering it back up it successfully booted all the way.
So, we have a very interesting glitch here with Apple’s Power Mac G5 machines. It would seem that if you have the system powered off and you attach certain devices via USB while the system is off, it gets confused when you first turn it on. Perhaps the PRAM keeps an inventory of USB devices and where they are plugged in that throws a fit if anything on those ports change while it’s off. Well, that’s what I think. It’s only a theory. Alternatively there might have been something going on with the printer; perhaps some funky USB-to-LPT converter wasn’t declaring itself properly.All that I know is the best thing to try if you have this kind of problem is to unplug the machine and all cables attached, hit the PMU reset ONCE, plug the power and keyboard only back in and then press the power button with your fingers crossed.
This reminds me of a PC that my fiances father owned that had a PCI USB port expansion card in it to add 3 more ports to the back of the PC. You had to plug USB devices in before turning the computer on or they wouldn’t be detected by Windows. Kind of the opposite of what’s going with this Mac. I’m sure fixing something like that would be a matter of a firmware update for the card itself but there wasn’t one available when I checked, nor were any updates available for Mac OS today. Anyway, it was a learning experience for me; its not too often you get a chance to attempt fixing a Mac hardware problem.
Tuesday, June 29th, 2010