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G5 quad processor compatibility.

ClintonGoodfellow

Active member
Hello!

Been having problems with an old 2005 g5 quad which I’ve owned for a while.

It didn’t work when I first got it. Played with the ram and got it running. Kept it on for a couple days and then restarted, then it never worked again after that. Temps seemed alright from memory.

Currently when you turn it on, the fans come on. No codes flashing on the front panel power led. The ‘checkstop’ led flashes briefly, ‘power on’ and ‘trickle’ leds stay on. Nothing happens on the screen and eventually the fans start running loudly. The ‘firmware good’ led never comes on. No other leds ever come on.

Im wondering if the logic board is at fault. Have tried smc resets, new batteries, diff graphics cards, diff ram, diff slots. Pretty much all the usual. One of my powermacs never had working sound, can’t remember if this is the one or not, so not sure if it’s not chiming, or whether it is but i can’t hear it do so!

I have a known working processor module from a 2005 g5 2.3 DP machine. I was wondering if this would be compatible with the quad to rule out the logic board?

The end plan, if I can get it running again is to rebuild the LCS.

Any advice would be greatly appreciated!

Cheers!
 

Byrd

Well-known member
I believe the DC 2.3 CPU will work (but jet turbine fans without calibration), however the issue might be the LCS has shat all over the motherboard and/or CPUs. I'd be taking it apart to see the damage first.
 

ClintonGoodfellow

Active member
Pulled the lcs from the machine as per manual. No sign of leakage on the logic board or where the water block mates with the top of the cpu. I didn’t however split the processors from the lcs for closer inspection.

Reinstalled the unit, powered it up and same results as before above, no sign of the ‘firmware good’ led coming on.

Worth trying the known good 2.3dp processor unit in it to check the logic board? If I get the same results would I assume the logic board is toast?

Weird symptom. With the machine turned on doing nothing, the fans actually slow down when the clear panel is removed to check the leds. Would have expected the opposite?
 

ClintonGoodfellow

Active member
Got some time and installed the known working 2.3dp processor onto the quad logic board. Same symptoms as before except the insert cpu b light is obviously now on. The ‘firmware good’ led never comes on and the machine never boots.

Can we assume the logic board is toast? Would a bad psu cause problems like this?
 

CircuitBored

Well-known member
Would a bad psu cause problems like this?

Possibly. This sounds similar to the issues my Quad was having when I first acquired it, which were remedied by a new PSU.

An easy way to test this is to warm the PSU up a bit and try booting again. Failing PSUs often struggle to start up when cold. Use a hairdryer set to low heat to pump some warm air into the PSU for about 30 seconds. I've used this trick on everything from Quicksilvers to theatrical moving lights and it almost always provides useful results.

You mentioned that you haven't rebuilt the LCS yet so I would like to state that this simply needs to be done if you want to actually use the machine, as these are seventeen year-old sealed loops that notoriously fill up with decomposed coolant. It is possible that your CPU waterblocks are so gummed up that they are overheating almost instantly.

Have you checked that the pumps in the LCS are actually working? They can get so blocked up that they actually stop spinning. Again, this will cause the machine to instantly shut off when powered.

Have you checked that the backside fan is working? There is a radial fan hiding behind the HDD cage that blows air over the heatsink on the backside of the logic board. If this fan dies, the logic board overheats and will itself die shortly after. In a similar vein: the thermal paste on the aforementioned heatsink needs replacing in order for it to work effectively.

Quads are tricky, troublesome, and require a lot of patience. They are, however, extremely fun and interesting machines when they actually work, IMO. The sound of a Quad booting cold is one of the most distinctive in the Mac kingdom.
 

ClintonGoodfellow

Active member
Hi, thanks for getting back to me.

Funny you should mention the psu, I had suspected it myself. With the 2.3 installed I was able to get at the terminals and measure the voltages. First round of measurements, they seemed low 3.3 was just under 3v. By the time I got back around to run through them again it was a steady 3.3v and the rest within spec. I do have a spare psu for these which was taken from a working machine, I suppose that should be my next port of call, but will def try the hairdryer trick first.

I do plan on rebuilding the lcs, but it was working well for a couple days with normal temps until I restarted the machine and it never came on again after that. I believe it to be doing something, but it clearly won’t be working at peak performance and will need remedied. Found some o-ring bits in and around the cooler. Can’t work out here they’re from as it hasn’t appeared to have been leaking. (Yet)

I can’t confirm the backside fan is working as it’s troublesome to get at. Is there a proven method in testing these, or should I just try powering it out of the machine whilst replacing the psu?

I am keen to get it running again and future proof it. It’s kinda a culmination of a particular era of apple machines so needs to be saved and maintained.
 

ClintonGoodfellow

Active member
Just spent a good hour or so putting in a known working replacement psu. No change whatsoever, machine behaves identically as before. I’ve replaced everything inside the case now other than the logic board. Ram, processor, gfx card, psu, the heap all swapped out.

Should I just go ahead and source a new logic board? There surely can’t be anything else I can try at this stage?
 

mg.man

Well-known member
I don't know if this is your problem, but years ago when I was repairing these, I found quite a few suffered from microfractures in lead-free solder used for the large "north-bridge-type" chip near the memory slots. I'm currently away, so can't send pics, but if memory serves, there is a heat sink on that chip with "sprung" plastic clips. The issue is similar to the Ring-of-Death issue XBOX consoles suffered from.

The real solution would be to re-flow the chip, but a stop-gap may be to take the "X-clamp" approach and use some machine screws (carefully!) to clamp down the heat sink with a little more pressure.
 

ClintonGoodfellow

Active member
I think you are correct, had suspected this myself.

Got some time and tried several things today with no avail. Tried a hairdryer on the ram slots are around that general area with gentle heat, tried pressing on various chips with a wooden dowel before plugging in power. No change, still exactly the same as it has been.

I don’t have a facility to reflow other than using my hot air rework station and hoping for the best! Was able to temporarily repair a few 360’s but as you say needs done right.

I might be interested in a board if you have one for sale. I’m based in the UK if that’s any use? Cheers!
 

mg.man

Well-known member
Sorry you've not got it going yet. I am on my way back to the UK today, so will have a rummage and see what I have. Feel free to PM or nudge me here if I get sidetracked! 😀
 

3lectr1cPPC

Well-known member
I don't know if this is your problem, but years ago when I was repairing these, I found quite a few suffered from microfractures in lead-free solder used for the large "north-bridge-type" chip near the memory slots. I'm currently away, so can't send pics, but if memory serves, there is a heat sink on that chip with "sprung" plastic clips. The issue is similar to the Ring-of-Death issue XBOX consoles suffered from.

The real solution would be to re-flow the chip, but a stop-gap may be to take the "X-clamp" approach and use some machine screws (carefully!) to clamp down the heat sink with a little more pressure.
I wonder if that's why my original dual 1.8 G5 logic board quit working after I removed the RAM for cleaning. I've since replaced the board so I know it wasn't anything wrong with the RAM (believe me, I tried everything I could before the nuclear option) but that could have been it I suppose.
Side note, not looking forward to the day when I have to recap the G5 boards. There have got to be about 50 SMD caps on the PMG5 logic board...
 
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