G4 Cube boots to black screen after grey Apple

MrCheeto

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Nov 2, 2008
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I have a G4 cube I've just installed Tiger on.

Now, once it boots, it will go to a blank screen once it should go to the blue screen.

It work 100% with a VGA monitor, but the Apple Cinema just isn't game.

Help pleeeease
 

MacTech68

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Mar 16, 2008
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Australia, Perth
Try resetting PRAM, three chimes at least.

Or, boot with the VGA monitor and select a resolution that the Cinema Display can handle, then shut down and connect the cinema display and try again.

If you can't determine supported resolutions for the Cinema Display, just select a really low res like 640 x ???.

Which Cinema Display is it? Do you have a method of testing the Cinema Display on another machine checking that all supported resolutions work?
 

MrCheeto

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Nov 2, 2008
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Did it all*

The only thing I can't do is test the machine with another ADC display or the display with another ADC-supportive Mac.

It's either the 23" HD or 20" Cinema Display.

The G4 runs fantastic with a VGA monitor and Mac OS 10.4.11 installed though!
 

MacTech68

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Mar 16, 2008
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Australia, Perth
Other than a PMU reset, I'm stumped.

Does the white light stay on (on the display) ?

Does Startup Manager work? (option key at startup)

Does Firewire Target Disk Mode work ?

What about entering Open Firmware and trying:

reset-nvram

set-defaults

reset-all
 

Macman756

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Sep 24, 2008
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Atlanta, GA
Did it all*

The only thing I can't do is test the machine with another ADC display or the display with another ADC-supportive Mac.

It's either the 23" HD or 20" Cinema Display.

The G4 runs fantastic with a VGA monitor and Mac OS 10.4.11 installed though!
ADC port on the graphics card is bad, or the VRM card is failing and not supplying the voltage needed to power ADC, (VGA doesn't need power from the Cube)
 

MrCheeto

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Nov 2, 2008
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Here's the process.

Press Power Button and the Mini Boots.

The display comes up to a white screen.

The screen switches to grey, then the Apple appears and the spinning load icon appears

When it appears that it should switch to the blue "Loading Mac OS X" screen, it instead just cuts dead to black. When it's black, the light on the display is on as well.
 

MrCheeto

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Nov 2, 2008
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OK, now a new problem.

I left the cube over-night in working-condition.

I left the PSU plugged in overnight, but not plugged into the Cube.

Now it won't boot! The drives won't spin at all! No sound except a really low quiet electrical hum!

To make matters worse, I posted online about my MacBook Air trackpad not working, and now it works flawlessly!

8O The demons have been exercised from my own MacBook Air into a new host-body! Mother of Jobs, help us all!!
 

Intell

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Jan 24, 2010
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You Cube's power supply is probably dieing. That could be why the Studio Display isn't working correctly. There is a thing you can try to get it working again. I forget the exact procedure, but it entails using a hairdryer to warm up part of the power supply. If that works, you'll have to do that every time you start the Cube up with a cold/room temperature power supply.
 

MrCheeto

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Nov 2, 2008
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That's odd, because I have my Blue's Clues skills and I can put two and two (and a third two) together and say that it doesn't make sense.

Cold start boots to black screen.

Warm start (plugged in all night, now it's warm) shows power button light and nothing more.
 

MacTech68

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Mar 16, 2008
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Australia, Perth
My final 2c,

As you've already noted, without another ADC Display card in another Mac, to eliminate the Cinema Display as a cause, or another Cube PSU or Cube internal regulator board, you're kinda snookered. You could end up chasing your own tail. :mad:

There could even be poor connectivity inside the Cube. Tarnished connectors/contacts. Who knows!?? :(

EDIT: I guess if you have an older AGP G4 tower, you could put the Cube's Display card in THAT and test the display. If it works, at least you'll know the Card and Display are ok.
 

MrCheeto

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Nov 2, 2008
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To make matters WORSER, now the G4 doesn't even have the power light! It will flash when you touch it but that's it! Dead!

This thing wants to be buried...
 

Intell

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Jan 24, 2010
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If the G4 is now refusing to start, I'm very sure its the VRM/DC-DC board. There are two or four little chips on them that die frequently. The last one could have died on your board.
 

MrCheeto

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Never mind. Tested the PSU. It checks out 100%
 
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MacTech68

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Mar 16, 2008
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Australia, Perth
Putting my multi-meter on the PSU's socket connector with the four pins, I read less than 1v and one of them gives me about 1.2v.

Is testing just as simple as touching the shield (ground) and one pin at a time, or is there an "on" state like ATX power supplies where you have to short one of the wires?
PSU is always on (when mains power applied).

Outer shell is only chassis gnd.

Power is two pins closest together (notched side) +28v

other two pins are GND or 'return'.

I repaired one once that had a faulty capacitor in the pulse width modulator. PSU work fine without a load but failed under normal load. Opening the Cube PSU case is a doozy. :eek:

EDIT: beat me to it.
 

MrCheeto

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Nov 2, 2008
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OK, so do you think that it was failing to power the display because it couldn't take the load? How would that explain the fact that it only cuts off once the Mac is booted?

How, then, is it that I can't even boot it now? Not at all! I just get a light for one second then it's gone.

What sort of status LED's should I look for inside? I see a green one at the bottom near the DC-in and a red one by the RAM.
 

MacTech68

macrumors 68020
Mar 16, 2008
2,187
152
Australia, Perth
OK, so do you think that it was failing to power the display because it couldn't take the load? How would that explain the fact that it only cuts off once the Mac is booted?

How, then, is it that I can't even boot it now? Not at all! I just get a light for one second then it's gone.

What sort of status LED's should I look for inside? I see a green one at the bottom near the DC-in and a red one by the RAM.
My reasoning was that it sounded like a resolution and color change was causing the failure.

Given the symptoms now, I'm suspecting a blown internal voltage regulator PCB, which doesn't sound good at all. If it is, then it's possible that 28v has been sent down the 3.3v rail to the motherboard. Not good. :(
 

MrCheeto

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Nov 2, 2008
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OK, here are the symptoms:

First, the Apple display would cut off right when the "Booting Mac OS X" screen should appear, but otherwise worked in Open Firmware and Disk Select.

Now, with any kind of display connected, when I press the power button, it will flash for one brief second, then fade. There are no mechanical sounds inside, just a slight whining, which I would expect from an old processor.

The whole time it's whining, there is a red LED by the RAM and a green LED across from it. If I hold down the power button after trying to start it, the whining will stop and the red LED goes out.

Troubleshooting tips?
 

Intell

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Jan 24, 2010
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After reviewing the Cube's service manual, I have some ideas. Have you tried resetting the PMU? Its the push button switch near the top of the logic board, it may be hidden by the video card. Push this switch one time. Also, make sure the PRAM batter isn't dead.

There is a green LED on the VRM/DC-DC board that turns on when the Cube is getting 28v from the power supply. If this LED is on, then the power supply is properly working as is some parts of the VRM/DC-DC board.

I believe there is also a hard drive activity LED inside the Cube.

There is a troubleshooting step that has similar problems you are having with it not turning on. The solution is to reseat the VRM/DC-DC board.
 

MrCheeto

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Nov 2, 2008
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Check check and check...

No activity LED, the hard drive acts like it's not even plugged in. Same with the optical drive.
 

Intell

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Jan 24, 2010
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If you've done all of that, then the VRM/DC-DC board is likely dead. Pull it and check for blown components. If you need to replace it, just buy another Cube. Buying just a VRM/DC-DC board alone is around $100.
 

Intell

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Jan 24, 2010
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My guess is that the VRM board was on its last legs and the ADC pushed it over the edge. This is why I don't use my Cube to power my ADC. I use one of those Apple ADC to DVI adapters.
 

Intell

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Jan 24, 2010
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VRM is another name for the DC-DC board. It's the board that controls the voltages within the Cube and changes the 28v into other needed voltages. It is located on the other side of the logic board than the ram sticks. It stands up and fits into a slot of its own.
 

MrCheeto

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Nov 2, 2008
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Yes I removed the magic widget and put it back into its bing blorp, nada.

Snap. Sad days...