IBM PS/55 Z – ATX Motherboard

16Jan/190

IBM PS/55 Z – ATX Motherboard

So, this ended up being a bigger hack than expected... but I'm happy with the result! I picked up this unit from eBay and hoped to use it as-is, but the motherboard wasn't healthy and Microchannel anything is impossible to find. I therefore replaced the guts with a DX2/66 motherboard! It all worked perfectly and I was happily playing games... but then I found a P166 at the markets and felt it was time for an upgrade.

Power Supplies

I picked up a Pico-ATX adapter on eBay rated at '120w' and had very little success with it. I could get it to boot without any cards... but as soon as I added anything on the ISA bus, let alone actual drives, I had zero action. Seems that it's just not up for the current required. I was also feeding it power from the internal 12v on the IBM's motherboard and this may have been overloading a single 12v rail.

It also needed a floppy connector... seems that these are for mini-atx boards where floppies are a distant memory...

Thinking that it just needed more amperes... I mounted a new 12v supply inside the monitor housing...

I grafted this onto the power rail to the front switch of the machine... it was rated at 110-240v, so there were no issues with step-downs...

This then meant the front power led was no longer lighting up, as the internal power supply had no current draw... I had to then use a resistor and put it on the 5v output of the new supply.

But... it still just didn't work... the actual Pico-ATX unit just wasn't up to the challenge of the old P166 motherboard! I then purchased the '160w' version off eBay, but it was EXACTLY THE SAME unit?

Slightly-larger ATX supply

I happened to be near an old PC shop in the city where I'd previously sourced a 'smaller' ATX power supply. Turns out they still had stock! I wasn't overly sure if it'd fit, but I was happy to have a spare in stock regardless. To my happiness, it fit perfectly!

I mounted it under the lid, as per the previous power supply, and ran the 110v in (flicking the voltage selector switch!) from the main power supply. The ATX cable was then fed straight down the back into the motherboard 'compartment'. It booted and the machine was back to normal... this time with W98SE and more horses!