CPU or Logic Board Needs Replacement–Which One

Question

CPU or Logic Board Needs Replacement–Which One

G4 MDD, Dual 1.25, 1 gig. After much troubleshooting, either the CPU or Logic board needs replacement. How do I determine which is causing the problem? Went through many pmu resets, logic board resets, pram zaps, ram eliminations and the two times it booted after three days of this, the pointer froze again on the screen. Oddly enough I ran TechTool after one of the boots and all harware passed. Rebooted and used for 1 hour before antother freeze. Therefore it is either the cpu or logic board. How do I tell?

( Also not a drive issue since I took it out and installed it in another G4 to write this message.)

G5Dual, 3GIG Ram,, Mac OS X (10.4), Also G4 MDD Dual 1.25 1 gig ram

Posted on Oct 24, 2009 9:28 AM

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Answer 1

Allan Jones

Level 9

68,690 points

Oct 24, 2009 6:54 PM in response to Patrick Corcoran

Have you checked to see if the computer is overheating? The Dual MDDs tend to run pretty hot and you could be experiencing thermal shutdowns.

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Answer 2

Oct 25, 2009 3:02 PM in response to Patrick Corcoran

Allan Jones wrote:
Have you checked to see if the computer is overheating?...

Temperature Monitor might be useful.

Maybe remove and replace the heat sink with some fresh thermal paste, after cleaning up the old paste. Just to make sure the CPU cooling system is in good shape and doing it's job. If it's dusty in the case, blow/vacuum it out as best you can.

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Answer 3

Oct 25, 2009 5:57 PM in response to Glen Doggett

Well then, why won't it boot after it has sat for hours and is not the slightest bit warm? In fact, I removed four of the empty card slot covers over two years ago to keep it cooler and the machine is dust free. I can try the heat sink fix but it just seems a stretch to think it is heat related. Where do I get Thermal Paste?

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Answer 4

Oct 25, 2009 6:15 PM in response to Patrick Corcoran

Patrick Corcoran wrote:
Well then, why won't it boot after it has sat for hours and is not the slightest bit warm?

maybe you don't have a heating problem at all, but something more serious with the hardware, just a suggestion to possibly help rule that out as one of the many potential culprits. How old is the PRAM battery? A dead one can cause booting problems.
http://eshop.macsales.com/item/Newer%20Technology/BAA36VPRAM/

Patrick Corcoran wrote:
In fact, I removed four of the empty card slot covers over two years ago to keep it cooler...

While this may increase airflow from the open PCI slots directly into the PSU exhaust, the cooling airflow through the CPU heatsink might be reduced. You might want to replace those slot covers and let the cool air in from the front/bottom get drawn up through the heat sink and then out the PSU exhaust the way the machine was designed to operate. Have you made any other mods to the machine?

lots of thermal paste options here:
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH &Description=thermal+paste&x=0&y=0

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Answer 5

Oct 26, 2009 11:59 AM in response to Glen Doggett

Ok. Removed the heat sink and will get some thermal grease and give it a try, with the slot covers back in. To the other poster, I am 100% sure it is not battery related. Tried it with three brand new batteries.

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Answer 6

Oct 26, 2009 5:15 PM in response to Patrick Corcoran

some info on applying thermal paste to the CPU, and tips on cleaning up the old gunk:
http://www.hardwaresecrets.com/article/274

Some typical precautions are to avoid getting the area wet and shorting out something, use sparingly the pure alcohol with little to no water content on a Q-tip, and avoid thermal paste with metallic additives that can be electrically conductive.

Sounds like something else going wrong if you can't boot cold with a brand new battery.

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Answer 7

Oct 27, 2009 2:30 PM in response to Glen Doggett

Ok, a wasted afternoon. Removed heat sink, applied new thermal paste, took drive out of this working machine and installed in dead machine and it still will not boot. The CD drive spins the OS disk, the hard drive is running, there is a red light on the logic board, the white power light stays lit but the machine will not boot. It does not chime or send a signal to the mouse. I am back to thinking it has got to be the logic board or cpu. Any other ideas?

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Answer 8

Oct 27, 2009 5:29 PM in response to Patrick Corcoran

You can't boot from an OS X CD/DVD in the optical drive after cmd-opt-P-R and holding down "C"?

Maybe a bad RAM stick or a bad optical drive? If you have a good machine you can try swapping parts out from that one, like it sounds like you were trying this already. Not sure if a bad logic board could do damage to any of those good parts that you swap out to test.

Ruling out one possible problem from the many options is not necessarily a wasted effort, if the machine is worth it to you.

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Answer 9

Oct 27, 2009 7:03 PM in response to Glen Doggett

When you boot any Mac the mouse immediately gets a signal the instant the power button is pushed as evidenced by the optical tracking lighting up. This isn't happening which is why I inquired about the cpu or logic board. Is it the logic board that checks for peripherals or the cpu? It is not the mouse or keyboard since I am typing on it right now on another G4. It could be that the power supply isn't supplying enough power, but that would not make sense since the fans are all going and the boot disk in the super drive is kerchunking and evidently spinning and attempting to load. That rules out a bad optical drive since the last time it did boot which was indeed a fluke after about 50 attempts to boot it, the computer ran for two days and I ran TechTool and it said all hardware passed. It could be flaky ram, but I will need to check that. But ram might be able to be ruled out if I know if the cpu or logic board sends power to the usb ports before even searching for ram. I wouldn't think on start up that the machine would prioritize ram in the sequence when it is available for reconfiguration whereas the the the kernal is going to run from rom before ram. Which all leads back to the death of the machine anyway which is that the arrow cursor froze on the screen after using the machine after a few days. It might be ready for the sledge hammer since I need to get a freakin new G5 anyway to run the new final cut pro, thank you Apple. I really wonder if I had invested all my money into Apple stock instead of their computers how I would have done versus my career. Mac SE over $3k at the time, Quadra 950, 9500, G4, G4MDD, G5 and a refurbished MacBook Pro for my kid. I must be nuts!

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Answer 10

Oct 28, 2009 9:33 AM in response to Patrick Corcoran

Patrick Corcoran wrote:
When you boot any Mac the mouse immediately gets a signal the instant the power button is pushed as evidenced by the optical tracking lighting up...

I'm not really familiar with details of the Mac boot up sequence and when ROM and RAM gets used, but as a point of comparison: I observed on my MDD after pressing the power button, a slight delay before the start up chime (external speakers on audio-output port) and then about 7 seconds before the light on my mouse comes on, plugged into keyboard, which is plugged into the built-in USB port. I think the start up chime and white/gray apple are built into the ROM, the Mach kernel gets loaded from disk, maybe some expert could clarify or confirm that, as to when RAM gets utilized or tested during the boot process.

Patrick Corcoran wrote:
I really wonder if I had invested all my money into Apple stock instead of their computers how I would have done versus my career. Mac SE over $3k at the time...

I'm with you there, I had one of those SE's in college, it cost more than a few years tuition. I imagine if I spent all that college tuition money on Apple stock, I could have retired by now! Apple's Time Machine just doesn't quite work like the H.G. Wells version.

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