'Wind-Tunnel' G4 (MDD) not booting

[AdrianK]

'Wind-Tunnel' G4 not booting​

Weird behaviour. When I try to boot the G4, I get no bong, but just a loud high pitched beep. Then the fans start whirring at high speed, and the Mac switches off. Nothing at all on the screen. It's supposed to be running Snow Leopard, though it's clearly not getting that far...
Help!

 

[AdrianK]

Have tried resetting PMU and replacing PRAM battery, but had no effect...

 

[MacsBug]

1st thing that I would recommend is to pull out the your RAM modules one at a time, and reseat them.

When you close the case make sure that the latch is closed properly
.
Next you should Reset the NVRAM on your G4.. This is different on the G4 than on other machines.

To reset the NVRAM:

• Power on while holding down the following 4 keys Command Option O F
• At the Open Firmware prompt, type: reset-nvram, and then press Return
• Next, type: reset-all and then press Return (your Mac should restart)

Once this Is done, hopefully your G4 will boot.

If your G4 does not boot after this please let me know which model G4 you have, and I can send you the service manual so you can further troubleshoot things.

 

[AdrianK]

I will certainly try what you suggest. The barrier may be that there seems to be no life at the monitor end of things A blank screen will simply mean I don't see an Open FIrmware prompt. However, tomorrow - I shall try.

 

[AdrianK]

I did exactly as you advised. Same loud beep, hurricane fan-speed, blinking power light and then powered off. Nothing appeared on screen despite open firmware keys depressed. The screen is good (Apple 17" Cinema Display,) just checked on another machine.
What could that loud beep mean??

 

[MacsBug]

According to the service manual a single beep means that RAM is not seen.

 

[AdrianK]

Ah. Now that's very helpful - thanks. I have tried re-seating the RAM. Perhaps I should now try replacing it...

 

[MacsBug]

One other thing the I read in the service manual is specific to the 17" display. It stated that if you have no video to try and disconnect all external firewire devices.

This is from the manual. "The power requirements for multiple FireWire devices and the Apple ADC 17" CRT display
may exceed the capacity of the power supply, causing it to shut the system down."

 

[AdrianK]

I replaced all four RAM sticks with those from another G4 and the machine started. It booted into a dialogue that invited me to type 'mac-boot' if I wanted to continue booting. which I did. The dialogue was black on grey, and small type, unlike Terminal's white type on black. I re-set the time in the sys prefs and restarted with Cmd-opt FO in order to reset the NVRAM, but the old pattern happened again - nothing on the screen, long beep, flashing power button, fast fans, and stop. Seems like an intermittent problem at best, But again - I'm stuck. Any further ideas?

 

[AdrianK]

And as for Firewire, I have nothing connected in addition to the 17"monitor other than K/bd and mouse. There's a PCI Firewire card. I could try removing that. (I now have. No change.)

 

[MacsBug]

Is the ram that you tried PC2700?

Also according to the service manual... "When no memory is installed The computer does not make a normal startup sound. Instead, you hear a single tone, and the LED on the front of the computer flashes continuously."

Here is a link to the Service manual.. https://app.box.com/s/jju17ey1nu2ygas183vgfkohkkqgbzfk

I also have the diagnostic Discs if you want an image of them. You would need another Mac to create the disc from the image.

 

[AdrianK]

The RAM was indeed PC2700. I'm getting the impression that the logic board isn't registering its presence. It's worked perfectly with the same internal set-up and HDs since new.
Thanks for the service manual link - most kind.
The machine is now not doing anything. No lights, no beep. seems like logic board to my untutored eye. I've taken it round to my local repair guy who's very expereinced and has spare logic boards in case that's waht he diagnoses.