Power Mac G4 MDD No Video

[bredfrown]

Hey there, everyone, I've got an G4 MDD I've had around for a few years that I thought I would dig up and try to get working again.

It was a dual 1.25 GHz G4 that I had to downgrade to a single 1 GHz G4 (after I fried the old CPU card back in 2012, I replaced it with a 1 GHz card from eBay in early 2022).

Anyway, here's where it gets strange.

The old CPU card that I broke would just cause the MDD to boot with the fans running at their max speed, with no chime, video, etc. Dead.

I swapped that CPU card out, and it would chime, respond to me holding the mouse button to eject the DVD drive, and I could hear the hard drive spinning, but I'm
not getting any video from my ADC display (I'm able to power this MDD via the power button on it), nor my Dell monitor via DVI.

Any ideas? I was thinking it could be PSU-related, but I'm not quite sure.

I currently don't have a PRAM battery in the MDD.

 

[herd]

What went wrong with the original CPU? A common way to troubleshoot is to swap parts with another machine to narrow down the possible problems.

Just based on your description, I would guess the problem is CPU related. There were several versions of the MDD, possible CPUs, heatsinks, etc. The 1.25GHz CPU would have a 167MHz bus speed, while the 1Ghz CPU probably was set up for 133MHz. You could try slowing down the CPU to see if that helps.

 

[bredfrown]

Hey there, Herd!

I was wrong in my original post, the other CPU card I have is a dual-processor 1GHz G4 with a 167 MHz bus.

Way back in 2012, I took the processor card out (can't remember why), and after putting it back in, the machine kicked up its fans at high speed. Also, there wasn't a chime or anything else either.

With the CPU I bought in 2022 (the dual 1GHz G4 with a 167MHz bus speed), it would chime, but no video.

I wish I had another one handy where I could test, but I don't at the moment.

This morning, I decided to put the original processor card back in just to see if I might've seated it incorrectly way back when, but the fans kicked up at full speed. I wanted to take it apart again to check the cards, and it appears that both bus speeds are at 167MHz, so I basically have one card that's 250 MHz slower (1 GHz w/ 167MHz bus vs. 1.25 GHz w/ 167MHz bus).

I took the RAM out – I had 2 GB, and have been testing each 512 module. Using only a single stick at a time, but no change. I have the 1 GHz CPU card in there now.

Does the MDD require two slots to be populated with RAM?

 

[RepairManiac]

The MDD will work with 1 DIMM installed. I would also start it up without any DIMMs installed - you should get a beep and the front LED to flash. If it does not change (meaning zombie), then you either have a bad CPU , mobo, or bad combination of parts.
There were many versions of the MDD 167Mhz boards used for the dual 1.25, however the Dual 1.25 processor module worked in both the MDD and MDD 2003 models. I can't seem to confirm the same for the dual 1Ghz CPU Board. Can you post the last four digits of the SN# from the 1Ghz processor board? I'm curious which one it is.