Help with crazy fans in Mac Pro

Question

Level 1

13 points

Help with crazy fans in Mac Pro

Hi,

I desperately need some help! I switched on my Mac Pro today and heard a little popping sound, followed by a minor burning smell. I immediately powered down. Now when I try to start, I get all fans on full power and no other response. No other lights etc, Main front light is on solid. I'm guessing its a PSU fault - and ideas on how to check?

Thanks

Extra info if needed:

Mac Pro 1,1 (2006) running ML via chameleon boot

2 x quad 3Ghz CPU (upgraded)

20gb ram

Ati radeon 5770 graphics card

4 x 3 tb HHD in raid 0 by newer tech controller card

Boot / installer partitions on HDD on IDE connector

SSD for OS on IDE connector

I have tried removing / disconnecting all possible components with no change in symptoms

Thanks for any suggestions.

Mac Pro, OS X Mountain Lion (10.8.2)

Posted on Nov 3, 2012 6:28 PM

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Answer 1

Nov 3, 2012 6:51 PM in response to king_stevo

The fans are set to maximum by Hardware at power on. In a working Mac, the running software resets the fan speed to more reasonable speeds based on measured temperatures multiple times a second. If the software stops running, the fans revert to high in a very short time.

The Chime is generated in software after the first part of the power-on self test has completed successfully. No chime memnas it never completed, but no idea how far it got.

If the only problem is not enough working RAM to start up, the power light blinks. (this presumes your Mac gets far enough to check RAM).

The side door is not interlocked, and there are no Hazardous Voltages available to your unaided fingers, but components may be HOT. An optical Drive Molex power connector will show just over 5 Volts and just over 12 Volts on the outer leads, with Ground on the inner black wires. There may also be diagnostic LEDs.

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Answer 2

king_stevo Author

Level 1

13 points

Nov 3, 2012 6:59 PM in response to Grant Bennet-Alder

Thanks for your input. The graphics card's fan comes on full instantly (and I know what you mean now, it usually does but then quickly drops). However, it's staying at full power and the other internal fans then join it shortly after at max speeds.

Sorry, I should have said, there is no chime. I don't think I'm getting anywhere near that stage. No LEDs on ram boards or anything.

I'll grab a multimeter this afternoon and test for power to the molex.

Can't see any other LEDs when power is on.

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Answer 3

king_stevo Author

Level 1

13 points

Nov 4, 2012 3:57 AM in response to Grant Bennet-Alder

Okay. So I get just over 12v on one side of the molex plug, but barely anything on the other. Certainly not 5v. So, does that mean my psu is definitely done? Is it repairable or must it be replaced?

Are they specific to model or would (for example) a 2008 psu fit and work in my machine?

If its a replacement, I've got my work cut out. Trying to find one of those here in china wll be a lot harder than you think it might be!

Would a second hand one be okay, or is this something that should always be new?

Thanks again for your time and advice.

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Answer 4

Nov 4, 2012 6:37 AM in response to king_stevo

The lengths of the wires will be an issue with any but an exact match, as the wiring harnesses changed with each major model. Sometimes several different suppliers were used for a given model, and PSU from a different supplier should work fine.

If a used one is what you can get, that is what you use. Some assurance that the replacement actually works is better. (it reduces complexity of what is trusted, what is unknown.)

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Answer 5

king_stevo Author

Level 1

13 points

Nov 6, 2012 2:42 AM in response to Grant Bennet-Alder

Am totally gutted. Got a new power supply, fitted it (man those connectors are fiddly to reach!) and the same thing.

I traced the ODD power cable back to the logic board and removed it. I then tested for voltages across the 4 pins and same thing. I get 12v but no 5v. So, the next question (that I'm scared to ask is) does this mean I've popped a capacitor or something on the logic board? In other people's experiences, are the logic boards repairable? Is it possible to get it properly tested without costing a fortune? I seem to be sinking money into this thing at the moment :-(

As always, ANY advice gratefully received.

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Answer 6

Nov 6, 2012 4:45 PM in response to king_stevo

It seems your logic board decided to commit suicide on you. Apple will do diagnostics on your Mac Pro for free but the cost of repairing the logic board will be expensive since your Apple Care expired. So, you have a choice of either biting the bullet and have them repair it or if you feel comfortable to do it youself and buy the part online and replace it yourself There are a few reliable online third party retailers such as www.powerbookmedic.com.

Good luck.

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Answer 7

king_stevo Author

Level 1

13 points

Nov 7, 2012 2:37 AM in response to JShimazaki

Cheers. I'm happy to do it myself - I've removed everything from the machine now anyway, so just need a new board to start the big rebuild!

Trying to source one here in china without having to go direct to apple who want about £450 for it...

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