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G5 iMac CPU fan controller bad

Message #1 - Posted 2009/01/04 - K Miller

Hello All. I could use a bit of advice on how to better cool my limping iMac.

I have a 3rd edition G5 iMac (2.1GHz with iSight) that has a fried CPU fan controller on the logic board - char marks and all. I replaced the fan itself to no avail - the new one either fried instantly or simply doesn't get the current it needs and the thing goes into thermal overload shutdown.

So I rigged up an external PC fan to blow into the small circular CPU fan intake on back (this is USB powered and runs continuously) and it works OK but it's crude and noisy. Anyone have an idea on how to better repair the machine? Or even how to wire this external fan so that it's speed is proportional and/or it shuts off at sleep?

Thanks in advance!

Message #2 - Posted 2009/01/04 - Jolly Roger

Previously, K Miller wrote:

Hello All. I could use a bit of advice on how to better cool my limping iMac.

I have a 3rd edition G5 iMac (2.1GHz with iSight) that has a fried CPU fan controller on the logic board - char marks and all. I replaced the fan itself to no avail - the new one either fried instantly or simply doesn't get the current it needs and the thing goes into thermal overload shutdown.

So I rigged up an external PC fan to blow into the small circular CPU fan intake on back (this is USB powered and runs continuously) and it works OK but it's crude and noisy. Anyone have an idea on how to better repair the machine? Or even how to wire this external fan so that it's speed is proportional and/or it shuts off at sleep?

Thanks in advance!

No telling where the short is occurring; so you may want to avoid powering the replacement fan through the same circuit.

I imagine if you can find a suitable place on the logic board to supply full power to the fan, you could get a fan with the same shape and size that runs at the full speed of the stock fan all the time and wire it up to the power source, and that would do the trick.

Send responses to the relevant news group rather than email to me. E-mail sent to this address may be devoured by my very hungry SPAM filter. Due to Google's refusal to prevent spammers from posting messages through their servers, I often ignore posts from Google Groups. Use a real news client if you want me to see your posts.

JR

Message #3 - Posted 2009/01/04 -

Yes finding another suitable place on the logic board to tap into for fan power is indeed my quest. Any suggestions?

I assume the original fan and it's replacement are both still good untis with the controller being at fault. I've contemplated tapping the harddrive wires or the DVD/superdrive but is that constant power? At least that way the fan would sleep when the machine does.

The wires of the original CPU fan are:

- Brown
- Black
- Gray
- Black

Any ideas on which wire is which? I'm assuming it's +12V to brown and both blacks are ground while the gray reports fan speed?

On 2009-01-04 13:09:11 -0800, Jolly Roger said:

Previously, K Miller wrote:

Hello All. I could use a bit of advice on how to better cool my limping iMac.

I have a 3rd edition G5 iMac (2.1GHz with iSight) that has a fried CPU fan controller on the logic board - char marks and all. I replaced the fan itself to no avail - the new one either fried instantly or simply doesn't get the current it needs and the thing goes into thermal overload shutdown.

So I rigged up an external PC fan to blow into the small circular CPU fan intake on back (this is USB powered and runs continuously) and it works OK but it's crude and noisy. Anyone have an idea on how to better repair the machine? Or even how to wire this external fan so that it's speed is proportional and/or it shuts off at sleep?

Thanks in advance!

No telling where the short is occurring; so you may want to avoid powering the replacement fan through the same circuit.

I imagine if you can find a suitable place on the logic board to supply full power to the fan, you could get a fan with the same shape and size that runs at the full speed of the stock fan all the time and wire it up to the power source, and that would do the trick.

Message #4 - Posted 2009/01/05 - Florian Zschocke

K Miller schrieb:

Yes finding another suitable place on the logic board to tap into for fan power is indeed my quest. Any suggestions?

I assume the original fan and it's replacement are both still good untis with the controller being at fault. I've contemplated tapping the harddrive wires or the DVD/superdrive but is that constant power? At least that way the fan would sleep when the machine does.

The wires of the original CPU fan are:

- Brown
- Black
- Gray
- Black

Any ideas on which wire is which? I'm assuming it's +12V to brown and both blacks are ground while the gray reports fan speed?

First, if you can't measure it, don't do it.
Second, if you don't have the right tool to measure it, buy one. Third, if you connect the wrong wire, the the machine will be dead and gone.
Forth, check all other possible options first. You could easily check the fans you got. A Motor is also a generator. It produces energy if you turn the wings. Better, try to connect it to a 12v source and see what happens. Fifth, try the hardware test first. Is the fan still seen by the system? Dose it report a bad fan? Post the error code form Apple-Hardware-Test here.

Greetings Florian

Message #5 - Posted 2009/01/07 - Fred Bambrough

In message <2009010521375516807-@news.hevanet.com>
K Miller wrote:

On 2009-01-05 08:27:35 -0800, Florian Zschocke said:

Is the fan still seen by the system?
Dose it report a bad fan? Post the error code form Apple-Hardware-Test here.

Thamk you Florian for your interest and advice. I have attached a screenshot of graphs from the (excellent) application "Hardware Monitor." The graphs depict a rising RED CPU temp that is not affected at all by the rising then pegged CPU fan speed.

Thank you for your abuse of Usenet.

Fred

Message #6 - Posted 2009/01/08 - K Miller

Apple Hardware Test (v.2.5.3) stops after the LogicBoard section with the error code:

"2FAN/4/8: CPU Fan"

I don't believe the CPU fan is actually turning, though the AHT documents indicate that all smart fans will run at full speed - and the other two certainly seem loud...

Thanks in advance.

On 2009-01-05 08:27:35 -0800, Florian Zschocke said:

Is the fan still seen by the system?
Dose it report a bad fan? Post the error code form Apple-Hardware-Test here.

Message #7 - Posted 2009/01/08 - Florian Zschocke

K Miller <nospam@nospam.com> schrieb:

Apple Hardware Test (v.2.5.3) stops after the LogicBoard section with the error code:

"2FAN/4/8: CPU Fan"

Ok, to make it sure that is not the FAN, test it in one of the other positions. I don't know if it possible with model. Could you connect it to the position of the lower right or left fan? Do they have the same connector?

Florian

Message #8 - Posted 2009/01/08 - K Miller

On 2009-01-08 12:06:09 -0800, Florian Zschocke said:

K Miller <nospam@nospam.com> schrieb:

Apple Hardware Test (v.2.5.3) stops after the LogicBoard section with the error code:

"2FAN/4/8: CPU Fan"

Ok, to make it sure that is not the FAN, test it in one of the other positions. I don't know if it possible with model. Could you connect it to the position of the lower right or left fan? Do they have the same connector?

Florian

The HDD fan and leads is the only readily accessible (while the machine is running) but unfortunately the connector for the HDD fan has only 4 pins (the CPU fan has 5 but only 4 wires used.) I'll try to jumper the HDD fan pins to the old CPU fan.

Kurt

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