Chosen Solution
I have a 2007 8-core MAC PRO. About two years ago, I got rid of the stock GPU and purchased an ATI Radeon HD4890 for it. All was working well until the other night all of the sudden the fan became very loud and started oscolating (cycling) between loud and less loud. About every second was the pattern of sound. The system will not boot now. No beeps, errors, etc. The only thing I see is that there are two small LED’s for CPUA and CPUB that are on, along with a label by them that says “overtemp”. Those are on. If I hit the little reset button by them, I can turn the led’s off. In diagnosing, I purshased another ATI 5770 single card slot and put that in. Still won’t boot up. I can also hear a very faint ossolating sound with this card too, but it’s definitely not as noticeable. I’ve pulled out the card and ram and tried running it. No beeps, etc. I’m thinking that it might be a bad PSU, but hate to buy one on speculation. Any other thoughts? Thanks
It sounds like the computer is overheating (Or even worse, thinking it is overheating) Check that the system fans are all working, and maybe remove the CPU heatsinks, and clean them out. Also, replace the thermal compound on the processors if you can. Powermac G5s would act up if one of their processors died, but still show some signs of function. If CPUA works, but CPUB is damaged, you may be able to boot the computer with only CPUA installed. (I would only try this after ruling out any other problems) Unfortionatly, I’m not incredibly familiar with these machines. The RAM wouldn’t all die at once, so that probably isn’t your problem.
You can resolve many system problems by resetting the logic board. There are three reset switches on the logic board that you can use to troubleshoot various issues: SMC reset: If the computer is experiencing a power issue, resetting the system management controller (SMC) may resolve it. RTC reset: If the computer is experiencing a booting issue, resetting the Real Time Clock (RTC) may resolve it. System reset: You can use this switch to determine if a computer that won’t consistently boot from a cold start has power supply issues. located in the upper right-hand corner of the logic board What are the diagnostic LEDs telling you? The LEDs are located toward the rear of the logic board, under the memory cage, next to PCI card slot 1. You can view these LEDs by removing the computer’s side access panel and looking through the memory cage to the logic board below.
I ended up having to send it in to have the logic board replaced ($600 repair). Not too happy, but that’s life I guess. Dave
I had the same symptoms, it was a USB3 hub, when i removed it the Mac worked fine, don’t know why it worked a few times before doing that though.
