Power Mac G5 power issues - Red lights on CPUs

gavinstubbs09

macrumors 65816
Original poster
Feb 17, 2013
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NorCal boonies ~~~by Reno sorta
I just got done rebuilding the LCS, and I noticed that I can turn on the Mac and get no boot, and a few minutes later the fans ramp up. Resetting the PSU gives me half a bong and no boot. Once I reseated the graphics card and got a full chime plus the white light in the front stayed on. Every other time use white light is off.

Any suggestions?

Update:
Got it to run after I rebuilt the LCS once more, and the fans still jump up then back down. CPU/A is pretty toasty while CPU/B sticks around 130*F. My best guess now is some sensor is broken so I am running the Service Diagnostics to check for sure.
 
Last edited:

eyoungren

macrumors Core
Aug 31, 2011
21,332
13,191
ten-zero-eleven-zero-zero by zero-two
I just got done rebuilding the LCS, and I noticed that I can turn on the Mac and get no boot, and a few minutes later the fans ramp up. Resetting the PSU gives me half a bong and no boot. Once I reseated the graphics card and got a full chime plus the white light in the front stayed on. Every other time use white light is off.

Any suggestions?
Try rearranging the RAM. G5s throw a big snit if they aren't in the right spot.
 

gavinstubbs09

macrumors 65816
Original poster
Feb 17, 2013
1,386
247
NorCal boonies ~~~by Reno sorta
I've taken the processor out a few times now, each time checking thermal paste/coolant in the system. This last time I put processor 2 in the top slot and number 1 in the bottom slot. Made no difference at all. The fans sped up as if it was turning on normally, then a bit later fans kick in 100%

What sucks is this thing worked before I took it apart to rebuild the LCS. I'm a but bummed!

Red lights on each processor card light up each time I boot, and from what I can find out is people with 2.5GHz systems where people check to see if it leaks, so possibly my processors are overheating? New thermal paste is on the cards too, Artic Silver 5.

I'm lost right now, tempted just to buy a 2.7GHz LCS off ebay or get a pair of 2.3GHz air cooled CPUs to throw in here.
 

Intell

macrumors P6
Jan 24, 2010
18,881
368
Inside
G5 logicboards typically cannot run with a different speed CPU in them. This is because the FBUS is locked to the CPU's speed. If you do put faster or slower CPUs than the original ones, it'll either not boot or be stuck in a kind of safe mode where the CPU runs at 900Mhz.
 

gavinstubbs09

macrumors 65816
Original poster
Feb 17, 2013
1,386
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NorCal boonies ~~~by Reno sorta
Good news! I got it to boot up and I can use the thing now! Typing this on it.

I went through and re-hosed the entire system but using the proper aluminum tubing rather than how I just used fuel line throughout the entire setup. However, CPU/A likes to sit around 160*F then randomly spikes to 170*F and even at some points up to 200*F. CPU/B is pretty stable and sits around 126*F. So I need to find a way to keep CPU/A cooler!


Could a temperature sensor be broken in which case reports that the CPU jumps 40 degrees within a second and the fans jump up then back down?

I'm going to run the ASD on here and then I can find out for sure.
 
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jrsx

macrumors 65816
Nov 2, 2013
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Tacoma, Washington
Good news! I got it to boot up and I can use the thing now! Typing this on it.

I went through and re-hosed the entire system but using the proper aluminum tubing rather than how I just used fuel line throughout the entire setup. However, CPU/A likes to sit around 160*F then randomly spikes to 170*F and even at some points up to 200*F. CPU/B is pretty stable and sits around 126*F. So I need to find a way to keep CPU/A cooler!


Could a temperature sensor be broken in which case reports that the CPU jumps 40 degrees within a second and the fans jump up then back down?

I'm going to run the ASD on here and then I can find out for sure.
Awesome! Good to hear that! Is the CPU that's spiking the one that seems to sit slightly higher than the other CPU?
 

iamMacPerson

macrumors 68030
Jun 12, 2011
2,747
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AZ/10.0.1.1
Awesome! I was getting a bit worried!

I'm not sure if the LCS G5s need it, but did you run the thermal calibration?

Also, do you still need those O-rings?
 

gavinstubbs09

macrumors 65816
Original poster
Feb 17, 2013
1,386
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NorCal boonies ~~~by Reno sorta
CPU A is the one that loves to get hot. I just got the red light on the processor, but only on the top, not the bottom.

I don't think they do but I am going to run it anyways just to see if something else is wrong just to make sure.

I do need those O-Rings but I just reversed the old ones and they seem to be holding in well, and I think they should at least last a week for the new ones to arrive!
 

iamMacPerson

macrumors 68030
Jun 12, 2011
2,747
865
AZ/10.0.1.1
CPU A is the one that loves to get hot. I just got the red light on the processor, but only on the top, not the bottom.

I don't think they do but I am going to run it anyways just to see if something else is wrong just to make sure.

I do need those O-Rings but I just reversed the old ones and they seem to be holding in well, and I think they should at least last a week for the new ones to arrive!
Ok no problem. They should be here some time early this week.