Powermac 7500/100 dead

[Dimitris1980]

I have a powermac 7500/100 and when i was trying to use toast deluxe 4 to run some 'toast files' the computer was stuck many times. I was using the power button to turn the computer off but nothing was happening and the only way to turn it off was to pull out the plug from the socket. Unfortunately the powermac doesn't work now. It doesn't turn on. What is the problem? The power supply was burned?

 

[johnklos]

I have a powermac 7500/100 and when i was trying to use toast deluxe 4 to run some 'toast files' the computer was stuck many times. I was using the power button to turn the computer off but nothing was happening and the only way to turn it off was to pull out the plug from the socket. Unfortunately the powermac doesn't work now. It doesn't turn on. What is the problem? The power supply was burned?

Since you're leaving out many details, then this is only based on the little bit of information you've given. Yes, it's entirely possible that the power supply is dead. What usually happens, though, is that the heat sink grease between the PowerPC 601 and the heat sink dries up and the processor gets cooled unevenly, and this leads to crashing and lockups (particularly when running the CPU at 100% like when you're running Toast).

When you say the machine doesn't turn on, do you mean that when you push the power button absolutely NOTHING happens?

 

[Dimitris1980]

exactly. nothing happens.

 

[phreakout]

When you pulled the plug to shut it off, you probably just corrupted the Power Management Unit. It is a small computer within the Power Mac 7500 that controls power flow throughout the logic board. One thing you could try is pulling the battery out of its socket (green and purple colored), put it back in again and press the reset button (located on the logic board near the processor card) for about a second. This will reset the PMU enough to get it powered back up. If not, go on to the next paragraph.

Start by unplugging your 7500 from the wall. Then open the case up. Next, remove ALL PCI cards that are installed. Then remove ALL of the RAM. Next, remove ALL of the VRAM cards, if installed. Plug the 7500 back into the wall and press the power button. You'll hear the sound of breaking glass shattering coming from the internal speaker. This is supposed to happen. After you hear the sound, turn the machine off and place ALL cards back in their proper place. The 7500 should now be back in working order.

What you've done in the above paragraph is about the same as giving a person a shock from a defibrillator. You shocked the Mac's heart back into normal rhythm. Take my word for this: I've used this many times on mine and it just works.

Give it a try and let me know how it works.

73s de Phreakout. :rambo:

 

[noidentity]

Seconded. I use a PowerMac 8500 all the time and its PRAM battery is dead, so I have to set the date each time I power it up (I turn off the outlet strip to it at night). Recently it would not power up. No response to keyboard power key or button on front. Unplugged, plugged back in, no response. Pulled the logic board and tried running without any hard drives, same thing. Swapped power supplies, same thing. Tried a second logic board and that booted, then I connected the original and it booted as well. Conclusion: NVRAM (the stuff Power Manager uses, not PRAM) was corrupt in some way it didn't like, but it somehow got into a different state. I imagine I could have gotten it to boot by holding the "cuda" button inside, which resets NVRAM.

 

[trag]

The failure to power up may be caused by corrupt NVRAM brought on by a flat battery, as the earlier posters suggest. However, the crashing you experienced is probably a heat sink issue as John suggested.

The heat sink grease Apple used on PPC601 chips dries out and stops working after a time, usually much shorter than now. Carefully, did I mention carefully, carefully, unclip the heat sink from teh CPU card. Examine the heat sink grease. It is probably white and powdering at this point. Clean it off with swabs and alcohol and replace with a small (small) dab of new grease. Do not overapply, as the stuff is only filling the tiny imperfections between the heat sink and CPU die caused by the two surfaces not being perfectly flat. If the stuff runs out onto the PPC601 pins it can cause shorts. I killed a PCC Power 120 motherboard this way many years ago.

Be careful when replacing the heat sink. Excess pressure can crack the CPU package. A common failure mode for PPC601s is for them to crack. Oh, while you're replacing the heat sink grease, you might look carefully for cracks in the CPU package. Your problem could be cracking rather than overheating, but I would bet on overheating.

The heat sink grease problem seems to show up most frequently on 7100s for some reason.

I had one back around '99 or 2000 that drove me crazy. It would run great for a little while and then crash or lock up. I replaced the system, etc. I don't know how many times. Then, once, it showed video artifacts which I recognized from an overheating system I had worked on and after that I found the worn out heat sink grease.