[G4] Power Mac G4 (MDD) Power Supply Replacement Notes

[Alan Kidner]

I recently rescued a Power Mac G4 (FW 800) Dual 1.25 GHz from the skip 
at work, purchased 2GB of second-hand RAM on eBay, installed the cards 
and drives from my Quicksilver and was running sweetly for about a week 
before the power supply unit (PSU) died.  

The machine is now up and running again using a standard PC power supply 
that I had in the attic.  It's noticeably quieter and the CPU is a 
little cooler (54oC).  Most of the necessary information came from a 
website previously mentioned on this news group.  However, I am 
submitting some notes below that may be helpful to anyone else who finds 
themselves facing the same problem.

Notes:
- New ATX PSU is 480W original was 360W
- I bolted the new power supply flush against the top of the case with 
the front edge against the collar for the top front, side panel fixing.  
My large PCI raid card would just fit in the bottom PCI slot.  Every 
millimetre was needed and the new PSU was a very snug fit!
    . . drill out front two pop rivets holding door latch assembly
    . . bend back the front corner fold on the door latch assembly (a 
thickness of metal too much!)
    . . remove front locating lugs from underside of plastic top cover 
(new PSU blocks the slots)
- I cut the connector and wires from the original PSU and soldered them 
to extension cables (see parts list below) so that the connection to the 
new PSU was above the optical drive bay.  Using the extensions means 
that the new PSU is left intact and can easily be replaced with another 
should the need arise.  
- Don't connect the white wires
- Expect two spare red wires on the ATX side
- There were 25 wires from the 24-pin connector on the G4 side. The thin 
orange wire was the odd one out connected to pin 6 together with another 
orange wire of normal thickness.  Connect this thin wire to the grey 
wire from ATX pin 8.  This is the Power OK (POK) connection.  Connect 
the thick orange wire from MDD pin 6 just like all the others i.e. 
matching to any on the ATX side of the same colour.
- There will be one spare black wire on the ATX side (I terminated one 
of the two on the 12v P4 extension)
- You will probably need to cut one or more of the disk drive power 
cables from the Apple PSU in order to extend those on the new one.
- I bolted a new mains socket in place on the back of the case and 
connected it appropriately to the new PSU.  Be careful with mains power!

Parts List (for any UK readers Maplin part numbers in brackets):
- ATX PSU
- ATX Extension (A21GF)
- 4 pin 12v P4 Extension (A46AK)
- Euro Mains Chassis Socket (HL15R)
- Euro Chassis Socket Cover (JK66W)
- 2.5 mm Heat Shrink Cable Sleeve (BF87U)
- Euro Side Entry Socket (JP19V) OR Right Angle Socket and lead (AP08J)
- Disk drive power cable extension (A27AB)
- 3.5mm Nut (to secure top bolt of case back cover after removal of old PSU)

Links:
Details of MDD to ATX power supply swap
     http://www.atxg4.com/mdd.html
     http://www.applefritter.com/node/23857
QuickTime movies for PSU removal and installation
     http://docs.info.apple.com/article.html?artnum=26259
The easy option Apple PSU exchange!  UK readers try VIS £90 + Carriage + VAT
     
http://www.applemacparts.co.uk/store/index.php?manufacturers_id=1355&sort=1a&filter_id=7603
UK electronics part supplier
     http://www.maplin.co.uk/