Dual G5 Powermac Resurrection

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pmjett's picture
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Joined: Sep 5 2005
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In a moment of weakness, I picked up a 2.0 GHz Dual G5. The price was good and I knew from the outset that it didn't boot. It chimes, the drive spools up, but no video appears. If you sit long enough the CPU fans accelerate to warp 9. Judging from Google this is a pretty common problem - but short on solutions. Some suggestions of failed logic boards and/or CPUs OR power supplies. I've got a known good logic board coming, and don't want to brick it. I'm checking to see if anyone thinks the G5's got a failure mode that would damage the donor logic board. I'd rather replace one part a time until it boots.

Any thoughts?

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gsmcten's picture
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Joined: Oct 4 2005
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Re: Dual G5 Powermac Resurrection

pm,

Sure sounds like a bad MoBo to me.
When you opened the case did you notice any scorth marks or areas?
Does it interior smell like burnt electronics?

Steven

(2x Dual 2.0 Gig G5's) Smile

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Steven (gsmcten)

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MaxTek's picture
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Joined: Dec 20 2003
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Re: Dual G5 Powermac Resurrection

I have one exactly like yours. After taking some parts out my G5 has had the coolant leak problem. Did you check for that?

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Joined: Dec 11 2011
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Re: Dual G5 Powermac Resurrection

The 2.0GHZ was air cooled. It's been a long time since I've worked on these, but I think you (nearly) always need the apple service diagnostics disc to calibrate the computer again after changing the board. If you don't, it will work, but fans will run at full speed. Keep this in mind if you replace the board and it works, but the fans run all the time.

pmjett's picture
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Re: Dual G5 Powermac Resurrection

gsmcten- Judging by the aggregate of google responses, the motherboard seemed the most likely culprit. I did not notice any failed components or traces- yet. Though something like a failed electrolytic would be hard to miss!

MaxTek- I understand that leaking coolant systems have indeed been an issue, but I think the 2.5 (?) and 2.7 (?) G5's are liquid cooled. I haven't pulled my CPU modules off, but I'm pretty sure they're aircooled. I do need to yank CPU boards and inspect everything.

smiggly- I recall reading about the calibration you mention. I guess I'm going to have to source a diag disc. Those fans at full tilt are pretty impressive, something I noted from this machine as it winds out. I could turn my ceiling fan off in the office!

So are my concerns about injuring the "new" motherboard if it turns out something else is broken unfounded?

mike

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eeun's picture
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Joined: Dec 19 2003
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Re: Dual G5 Powermac Resurrection

pmjett wrote:

Though something like a failed electrolytic would be hard to miss!

They can be sneaky little fellows. I've done successful repairs to trashed monitors and motherboards by replacing caps that had no visible bloating or leaking. Especially with LCDs, if there are no visible problems on the boards, my first go-to is always the capacitors.

Could be quite a number of other things, though. But to rule out factors outside the mobo that might affect its replacement, you might want to check your voltage levels on the power supply with the old board installed and running (at least to the extent it runs). That way you're testing under some load and should get accurate readings from the supply.

Hopefully you won't need it, but here's some info on the G5's power supply:
linky

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Bob Hope's picture
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Joined: Jun 17 2012
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Re: Dual G5 Powermac Resurrection

Hi,

Overall, I see that the failure rate of many of the older PM G5s is quite high for logic board failure.

Does anyone know why that is?
I've got a dead PM G5 Dual 1.8 Tower, which had extraordinarily low usage over the years ...

I was shocked when it failed a few months ago. Looking around online, indications are, it is likely the motherboard.
Wondering if there is any reasonable way to get it back into operation at low cost?

Seems like such a waste at this point.

Thanks!

Bob