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A Mac Issue


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So I am working on a mac g5. I have not worked on very many so my knowledge is limited. So here is the issues and steps I have taken to try and fix the issue.

When the mac was brought in it would:

  • Chime the mac boot up sound
  • Not show any video
  • fans will start normally but after awhile would spin up to full rpm

What I have tried:

  • Reseting the pram
  • Reseting the pdu
  • checked the onboard battery for 3.5 volts
  • started without the battery
  • tried new ram

After some more diagnosing, the Mac will start once out of every 10 times it starts. (This is just a rough estimate. Not actual) Even when it does boot after about ten minutes it will freeze, and fans will be at top rpm. Then when I try to reset it, sometimes it will not boot with no mac chime, not boot with mac chime, or boot with mac chime. It is very random. I am very clueless as I have not had many times to work on a mac. What would you say is the problem? The logic board, cpu, pdu or something else? I have disconnected both hard drives and still received the same issue.

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When is the last time the cmos batter was changed on the device?

Can you boot off external media? Like a live linux disc or mac install disc? Just curious is it still has the same problem off live media. If so, something definitely hardware wise is out of whack.

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It sounds like you may have some hardware problem.

1) Is the power supply overheating at all?

2) Make sure the CPU Fan is sitting properly.

3) Make sure all cables are clean and in good condition!

4) If else fails, it could well be the CPU or Mobo, that's causing the lockups/freezes

Edited by Infiltrator
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it does not seem to be heat because it will do the same thing right away when i turn it on. I could leave it running when it does not show anything then i will restart it and at times it will show something. Other times when I start it right away it will work. I can not find a pattern as to when it does work correctly.

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But it does this even when trying to boot off other media, or only when booting from the HDD? What happens when booting while HDD unplugged from board? (Obviously no OS to boot, but wondering you get a blank screen still)

Edited by digip
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I would get one of the power supply tests that are like 5 bucks or sneak up to the computer shop and use theirs to make sure the power supply is good

when you say no video does it show up on the network?

If it does not show up on the network I would start checking the motherboard.

If its on the network then you are just having a video card issue which goes back to testing that and the powersupply.

Edited by leapole
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I personally would not think it was the video card because at times the mac would play the start up chime with no video, other times it would not play the start up chime both without video

So how does that rule out the GPU? Worth a shot looking into. Any hardware failure on boot, generally causes some sort of beeps. No beeps is usually worse than no post at all. But MACs are a little different than a pc, and I don't have enough experience with them. I've never owned one or taken one apart, but would gather, basics are still the same. Does this machine allow you to put a different GPU in?

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Which model G5 is it? Here's the troubleshooting steps for the June 2004 and Early 2005 models.

Power-on LED illuminates when power button is pressed, fans spin, and boot tone

chimes, but there is no video

Reseat video card. (Make sure video card is fully inserted in connector and end of card is

secured by the connector latch.)

Reset PRAM (restart computer while holding down Command-Option-P-R keys until second

boot tone chimes)

Replace video card

Reset logic board. Refer to “Resetting the PMU on the Logic Board” in this chapter.

Replace logic board

Resetting the PMU on the Logic Board

The PMU (Power Management Unit) is a microcontroller chip that controls all power functions for

this computer. The PMU is a computer within a computer. Its function is to:

tell the computer to turn on, turn off, sleep, wake, idle, etc.

manage system resets from various commands.

maintain parameter RAM (PRAM).

manage the real-time clock.

Important: Be very careful when handling the logic board. The PMU is very sensitive and

touching the circuitry on the logic board can cause the PMU to crash. If the PMU crashes and is

not reset, the battery life goes from about five years to about two days.

Note: For the location of the PMU reset button, see “Logic Board Diagram” in the Views chapter.

Many system problems can be resolved by resetting the PMU chip. When you have a computer

that fails to power up, follow this procedure before replacing any modules:

1. Disconnect the power cord and check the battery in the battery holder. The battery should

read 3.3 to 3.7 volts. If the battery is bad, replace it, wait ten seconds, and then proceed to


2. If the battery is good, go directly to step 2.

Press the PMU reset button once and then proceed to step

3. Do not press the PMU reset

button a second time because it could crash the PMU chip.

Wait ten seconds before connecting the power cord and powering on the computer. If the

computer does not power on, there is something else wrong with it; refer to the “Startup

Failures” section of “Symptom Charts” in this chapter.

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