MDD FW800 PSU replacement: No picture.

[Dt990]

In my quest to build out OS 9 bootable powerhouse, I learned why these machines were called the wind tunnel. I wanted to make this thing quiet and looked into the ATX power supply conversions.

I watched Action Retro's Ultimate PowerMac G4 (time stamped to the part where he replaces the PSU) and bought the FSP Mini ITX Solution/Flex ATX 500W as he used and the premade conversion cable.

Quick specs:
Crucial MX500 SSD as the boot drive using SATA -> ATA StarTech converter
2 GB of RAM
ATI Radeon 9000 Pro

I made the classic mistake of organizing the cables before testing. The computer would chime but wasn't outputting a picture. I plugged in the original PSU and sure enough, it booted fine. I tried again with no dice. I decided to get a bit smarter, and booted off the old PSU and turn on file sharing so it'll pop on up on my network, then go back to the old PSU.

It's not booting as near as I can tell. It'll chime and that's about it.

Someone on a discord speculated that perhaps the GPU needs ADC to properly boot. It also could be a bad cable. It's unclear to me.

 

[reddrag0n]

what video connector are you using on the ati 9000? if you have the ADC plugged in while booting with the new psu, then that's your problem. if you hook up via dvi or vga then the new psu will work just fine as it's not supplying the +28v for the adc power connector on the video card. also check ATX G4 for their cable conversion for the mdd. just to make sure the cables you have on the adapter match up to the cables on the new psu

 

[Dt990]

what video connector are you using on the ati 9000? if you have the ADC plugged in while booting with the new psu, then that's your problem. if you hook up via dvi or vga then the new psu will work just fine as it's not supplying the +28v for the adc power connector on the video card. also check ATX G4 for their cable conversion for the mdd. just to make sure the cables you have on the adapter match up to the cables on the new psu

I forgot to mention using DVI to HDMI.

 

[reddrag0n]

I forgot to mention using DVI to HDMI.

could be your adapter. i have a few dvi to hdmi adapters and only 1 or 2 of them work like they should out of the whole lot

 

[Dt990]

could be your adapter. i have a few dvi to hdmi adapters and only 1 or 2 of them work like they should out of the whole lot

I doubt that’s the issue, as the same cable works off the default PSU, I’ll try the other dvi to hdmi cable but I don t think the computer is fully booting with the atx PSU. It chimes.

 

[reddrag0n]

then best bet, refer to this thread for help with your psu adapter. has to be a wire or two that's out of whack

G4 MDD ATX PSU Conversion

 

[Dt990]

then best bet, refer to this thread for help with your psu adapter. has to be a wire or two that's out of whack

G4 MDD ATX PSU Conversion

That's my thinking, I might just buy a different PSU and see if that'll work, I did notice mine has a 24v instead of 12v as marked by the pin out but I thought 24v is the norm on all ATX

 

[reddrag0n]

That's my thinking, I might just buy a different PSU and see if that'll work, I did notice mine has a 24v instead of 12v as marked by the pin out but I thought 24v is the norm on all ATX

that may work for the +25v line. if it has 12v also, see if you can configure it with an adapter

 

[helmetguy]

Did you get this working in the end? Changing the PSU worked for me when trying to adapt an ATX PSU to the MDD, but not before I went through two other ATX PSUs with the same result (starts, chimes, but no video signal).

In this case I used a 24-pin ATX extension lead and swapped the pins at the motherboard end to the MDD's pinout. The extra two +12V wires and ground wire that the MDD uses were taken from the 4-pin CPU connector on the PSU.

The first PSU was a Silverstone ST45SF-G (the one I wanted to use as it's SFF), the second was an XFX XPS-750W-3XS and the third (the one that worked) was a junky old Enermax ENB500AWT that I got from a recycler.

The first two PSUs were taken from working Windows machines, so they were known good PSUs.

I don't know enough about ATX PSU circuits to know why this happened, but hopefully this is useful info for someone.

 

[SASDakota]

I had this exact response from my MDD and Radeon 9000 pro after switching to this PSU: https://www.amazon.com/gp/product/B0BZHNR2HC

My MDD boots with a 7800gs as a GPU, I am now working out a graphical bug with the 7800gs due to the ROM flash.

Made my own conversion harness using the ATXG4 website pinouts.

 

[helmetguy]

There's a 9000 Pro in my MDD as well. OP's machine also has a 9000 Pro. Interesting.....

Unfortunately I don't have other video cards to test.

 

[helmetguy]

Since my last post I've got my hands on several G4-compatible video cards.

I was able to get my MDD to show video with a Geforce2 MX and the aforementioned Silverstone ST45SF-G, the one that gave no video with the Radeon 9000 Pro.

No idea why this 9000 Pro is evidently so picky about PSUs. It doesn't seem to be a wattage issue as the XFX PSU I tried, that also didn't work, is rated for far higher wattage than the stock PSU on all rails.

It doesn't seem to be an ADC issue either as I've had the 9000 Pro working with an Enermax PSU, with no +25v connected at all.

I guess if you ATX-swap a G4 and get no video - change the video card.

 

[Dt990]

Since my last post I've got my hands on several G4-compatible video cards.

I was able to get my MDD to show video with a Geforce2 MX and the aforementioned Silverstone ST45SF-G, the one that gave no video with the Radeon 9000 Pro.

No idea why this 9000 Pro is evidently so picky about PSUs. It doesn't seem to be a wattage issue as the XFX PSU I tried, that also didn't work, is rated for far higher wattage than the stock PSU on all rails.

It doesn't seem to be an ADC issue either as I've had the 9000 Pro working with an Enermax PSU, with no +25v connected at all.

I guess if you ATX-swap a G4 and get no video - change the video card.

Interesting, I’ll try the PSU with the 9600 Pro since I had to tape the ADC heads off on it.

Downside is I’m pretty sure that GPU isn’t os 9 compatible.