Power Mac G4 Mirror doors 2x1.25Ghz: doesn't start up

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Power Mac G4 Mirror doors 2x1.25Ghz: doesn't start up

Hi everyone!

I have an old Powermac, which I haven't turn on for a few years, and when I turn it on now it reveals an issue that maybe you can help me identify and solve.

When I turn it on, and while it is starting, after just a few seconds the fan noise increases substantially (much more than the usual loud fan noise this computer in famous for) and then the computer turns itself off, leaving the power button with the white light pulsing, as it does whenever we click to sleep mode.

I thought it could be the thermal grease that had dried, I checked and it was indeed dry, I cleaned it and replaced it with new grease but the problem remains.

I've taken the disks out, one at a time (I've 2), I've taken the RAM modules out (I've 4), two at a time, and I took out the PCI cards I had installed, to see if any of these things were causing the problem but I didn't notice any differences.

I've cleaned the fans, they were alright but now are like new, and the case air inlets.

In the few times I've tried this, sometimes I can see the menu but most of the times I don't get to see the menu, it turns itself down (sleep?!) before that.

Thanks in advance for your input!

Current Pro Desktops

Posted on Apr 26, 2022 1:53 AM

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Answer 1

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Jeff

Level 6

12,362 points

Apr 26, 2022 8:08 PM in response to Fr@ncisco

Try resetting the PMU (Power Management Unit) chip. Since the computer has been disconnected from power for several years, the internal battery on the motherboard is undoubtedly dead and should be replaced. It's a 3.6-volt, ½AA lithium battery.

1. Touch the grounded metal on the rear of the case, then disconnect the power cord and open the side panel.

2. Replace the battery. After 10 seconds, press the PMU reset button once and only once. It's located beside the ATA connections.

3. Close the case and reconnect the power cable. Press the power button and hopefully, the startup problem has been corrected.

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Answer 2

Allan Jones

Level 10

80,860 points

Apr 28, 2022 9:00 AM in response to Fr@ncisco

Welcome!

The two weak spots in the MDD are the power supply and the front panel board (FPB). Your symptoms call to mind both to this MDD owner.

The original 400W PS were reliable but noisey. The 360W versions that replaced them were quieter—albeit not by much—but more prone to failure. We have two MDDs; one's PS has already been replaced and the other needs the same service.

The MDD's front panel board holds the power button. Used/pulled FPBs are usually available and not too pricey but there is a possible workaround based on where your push the button in this archived Apple article:

Power Mac G4 (Mirrored Drive Doors), Power Mac G4 (FW 800): Power Button May Require Firm Push

There is also an at-home test if your have/can borrow one of the original USB keyboards. The M2452 USB Keyboard that shipped with the first iMacs had a power button like the old ADB boards. You can often find the them for a couple of dollars at thrift stores. The M2452 was the ONLY USB board with a power button. If you decide to buy one, make certain is it properly described.

If you connect the M2452 board to an MDD, the power button on the M2452 overrides the power button on the FBB. An MDD with a bad front panel board (FPB) will often start and then shut down as you described. Rather than replace the FPB, a lot of MMD owners left the M2452 attached but tucked out of the waywhen not needed, and never replaced the flaky FPB.

There are power supply pin-out tests for MDDs described here:

http://www.jcsenterprises.com/Japamacs_Page/Blog/D275729F-09DA-4FBB-96B3-BEEEB2C04619.html

Read the text and precautions fully.

EDIT: Due to a forum glitch I got logged out before completing my entry and seeing your more recent addition. The "Restart..." screen with multiple languages is due to a kernel panic (KP). KPs can be caused by many things but are more commonly due to hardware faults. Of those, the most common is incompatible RAM, bad RAM, or partially seated RAM. I know you've addressed this but recheck that there is nothing hiding in the slots and that the RAM is the right spec:

PC-2700 2.5v, unbuffered, 8-byte, nonparity 184-pin DDR SDRAM

You may have to test with pairs or modules removed. If the modules are different makes, test the same make together,

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Answer 3

Fr@ncisco Author

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Apr 27, 2022 10:34 PM in response to Fr@ncisco

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Answer 4

Fr@ncisco Author

Level 1

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Apr 27, 2022 10:32 PM in response to Jeff

Thank you Jeff!!

The internal battery was indeed dead.

Did it like you wrote and unfortunately the loud fan noise is still around and although the machine behaviour is different I still didn't manage to make it work.

The first time all I got was the restart grey screen — "You need to restart your computer. Hold down the Power button...".

Repeated the process again, and again the restart grey screen.

Another try, this time no restart grey screen and the computer stayed on, loud fan noise but didn't shut itself down like it did a few days ago. But went nowhere, didn't start the operating system, just a light grey screen without the Apple logo.

Another time, lines of text on a white screen, "Welcome to Open Firmware... to continue booting, type "mac-boot" and press return".

I did type "mac-boot + pressed return" but the keyboard wasn't responding and I had to shut it down, pressing the power button for a few seconds.

Another try, a mixed screen — black and kernel lines of text.

Another try, finally the macos opened, really fast, I got to see my desktop and folders but it was frozen, no mouse or keyboard reaction.

(loud fan noise still)

This was the only time I saw my desktop for so much time during this all process.

Tried a couple more times but all I got was the "restart screen".

Does this tell you anything? Still PMU? Logic Board? Power supply?

This machine was just fine the last time I worked with it!

... 6 or 7 years ago.

; )

Thanks in advance!

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Answer 5

Fr@ncisco Author

Level 1

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May 6, 2022 2:53 PM in response to Allan Jones

Hi Allan!

Thank you very much for your great input!

Ohhhh… I had one of those M2452 keyboards, with the power button, and I threw it away for tech recycling when one of the keys died.

I wish I had it now, but my feeling is that the front panel board is not the issue here.

During a few of the more recents tests the computer hold on for a while and didn’t turn off on its own.

This is a strange issue because this mac is constantly moving the goal posts.

At the beginning the problem was that the computer turned itself down (went to sleep actually) before the system fully started.

Then the kernel panic screens start to appear.

Recently those kernel panic screens didn’t show up again.

Maybe it was something like what you mention, a partially seated RAM or something like that, and since I’ve opened this machine so many times that issue went away.

Now, the most recent observation, the system starts and I can see my desktop, move the mouse and click in one menu or window… but after approximately 20 seconds the system freezes and I have to turn it off.

I will check the RAM again, to make sure they have the right specs.

They should be alright because they’ve been there for a bunch of years… but maybe one of them died.

The power supply pin-out tests is probably the more advisable thing to do but I don’t have the skills for that… the multimeter is still a strange machine to me.

I’ve had it in my amazon cart before but I thought it had a big learning curve for me at this time and I “saved it for later”.

I’ll try to get a more qualified help for that task!

The only constant is the fan that accelerates a lot and doesn't go back to normal...

I don’t want to give up, this machine has been around for 20 years, it’s the least I can do for her.

: ))

I'll try your suggestions and a few more and if I find out the problem I will post it here so that other can use this info too.

Thank you all!

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Power Mac G4 Mirror doors 2x1.25Ghz: doesn't start up

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