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Possibly recover from a dual CPU failure on a Mac Pro Desktop Macs
When I tried to boot my Mac Pro recently, it failed -- all I got was a black screen and a chime. I opened the case, and on the motherboard, I saw two LEDs were red: the cpuA and cpuB failure lights.

My warranty is over, but here are the steps I followed to get it working again:
  1. Turn off your Mac and unplug the power cord.
  2. Remove the CMOS battery on the motherboard (just above the graphic card).
  3. Wait 10 seconds -- I'm not sure if this is necessary, but it worked for me.
  4. Plug the power cord back into the Mac.
  5. Press the power button. The Mac should boot normally and give you the startup chime, but you want your CMOS battery back.
  6. Turn off the Mac, then unplug the power cord again.
  7. Put the CMOS battery back in.
That's it; boot and enjoy!

[robg adds: I've never seen this on my Mac Pro, and I'm not sure if it's a sign of a failing CMOS battery, or something else. I'm publishing the hint because (a) it may help someone in the same situation, and (b) to see if anyone has any idea of what may be behind an apparent failure of both CPUs. Please comment if you have any thoughts.]
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Possibly recover from a dual CPU failure on a Mac Pro
Authored by: harleyb on Aug 26, '08 07:58:32AM

Be extremely wary of this hint; older Apple models would be permanently damaged by being run without a CMOS battery. YMMV and you may very well break your computer.



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Possibly recover from a dual CPU failure on a Mac Pro
Authored by: Mac112 on Aug 26, '08 09:21:41AM

Some years ago I saved a lot of G4's in a similar way. The machine wouldn't start, and the start button pulsated. Power cord out, battery out, count to ten, battery back, power cord in, start!



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Possibly recover from a dual CPU failure on a Mac Pro
Authored by: johnsawyercjs on Aug 27, '08 04:08:17AM

Permanently damaged? Absolute nonsense. Where did you hear this? I've been fixing Macs since 1985, and removed batteries from thousands of them, and run many without batteries, and none have ever been damaged as a result. When the battery dies, it's the same as running without a battery, and the Mac doesn't die under that condition either. It's not cool to start or perpetuate a completely untrue rumor which makes people leery of trying a troubleshooting method that often works, when PRAM/NVRAM is scrambled. If you've had Mac die after you removed its battery and powered it up, it had other problems, and/or you zapped the logic board with static electricity buildup on your body, etc.

To reset a Mac's PRAM/NVRAM/Open Firmware/PMU/SMU etc. chip(s), I would first try other methods since they're easier, for most people, than removing and reinstalling the internal battery. I'd reset them from the keyboard first, following the Mac model's particular power manager reset process, if just unplugging and plugging in the AC power cord didn't help (and in fact just unplugging the AC cord is the method for resetting some Mac models); if those methods didn't help, then I'd press the logic board's reset button. As far as a "CMOS" battery's health goes (it should be called a lithium battery, referring to the battery type, not to the type of chip it's powering, since so many other chips in a computer are also CMOS, not just the clock/calendar/PRAM/NVRAM chips), you need to measure its current-delivering capacity, not its voltage, since a bad battery may still measure full or nearly full voltage of 3.6 volts. If the battery's current-delivering capacity is at or near zero, it should be replaced, or else reinstalling it may just make the Mac act up again.



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Possibly recover from a dual CPU failure on a Mac Pro
Authored by: ghay on Aug 29, '08 12:14:40PM

Did you not ever come across the LC475?

That was post 1985, but try removing the battery or letting one die - the Mac will not boot without it. Common problem at the time....



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Possibly recover from a dual CPU failure on a Mac Pro
Authored by: osxpounder on Sep 02, '08 09:58:04AM

Still, that's not exactly permanent damage, one must admit.



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Possibly recover from a dual CPU failure on a Mac Pro
Authored by: sipatel on Aug 26, '08 02:48:36PM
The thing to do is leave the battery out for a minimum of ten minutes, put the battery back in and then power up...

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Possibly recover from a dual CPU failure on a Mac Pro
Authored by: johnsawyercjs on Aug 27, '08 04:09:46AM

Waiting ten minutes isn't needed by the vast majority of Macs--only a very few.



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Possibly recover from a dual CPU failure on a Mac Pro
Authored by: delight1 on Aug 26, '08 09:29:07PM
I'm not sure if this is helpful, but while reading the article, i was reminded of this apple help doc: http://support.apple.com/kb/HT1806


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Possibly recover from a dual CPU failure on a Mac Pro
Authored by: fredpoint on Aug 27, '08 06:25:00AM

typo: chime -> no chime

I have tried to reset PRAM and SMC first but they didn't help.

The thing which apparently break my mac was a low level linux kernel hacking. I probably wrote irrelevant datas in the wrong place... I was playing with fire and I burn myself :)



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Possibly recover from a dual CPU failure on a Mac Pro
Authored by: ghay on Aug 29, '08 12:13:07PM

If you are having problems with your Mac booting, and you go and reset things - you can do serious harm - or at the very least - make fixing it a lot harder.



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