Friday, December 09, 2016

PC Power for the Vintage World

Question: What incredibly useful thing can you do with a PC power supply and just a paperclip?

Answer:  Build an incredibly useful Power Supply for your Vintage S100 Bus Computer.

The Issue
So the S100 Bus computer is going to make use of 5V 12V and 8V and 16V Power rails in the following way:

5V and 12V is DC power supplied to peripherals like Floppy Disks and Hard Drives

8V and 16V is supplied to the S100 Bus card cage

The Overall Plan
Is to repurpose the PC power supply to feed all the diskette and Hard Driver peripherals in the computer.  Meaning 5V and 12V. Particularly troublesome is (say) a 30 year old plus spinning or stuck hard disk.  Don't let this current overloading device bust up your ageing and difficult to replace S100 bus linear power supply.

This solution does not address the 8V and 16V feeds the idea is those still get fed from your old 1980's style PSU.

So get a PC Power supply and look at the Motherboard power connection:

You simply need to ground the PS-ON wire because otherwise your power supply will not turn on.  Most conveniently a ground pin is adjacent.  So with the paperclip I cut into a U shaped wire I short between PS-ON and Ground.

Now cover the whole connector in insulating tape or duct tape so it can't otherwise connect and short out.

PSU Placement

Rather luckily the Case /just/ has enough room for the PC power supply inside the old 1980 case ..

A really tight squeeze

With the Computer off and just the PC Power Supply on the HXC emulator springs to life.  Meaning that it looks like the peripherals are working fine.

Let's Test
A link is made from the RS232 Serial connection via a converter to USB and thence to a Windows computer running the popular Putty terminal emulator.   Use Device Manager as necessary to determine the relevant COM: port to use in the Putty configuration

Now power on

Since the A; command worked we can tell that the floppy drive is working and this is powered from the PC power supply.  

For Cromemco RDOS (or DDOS here) the single semicolon after the A means 8" disk drive  (or in my case emulated 8" disk drive).  Had it been  A;;; with 3 semi colons it would have meant initialise the 5.25" diskette drive instead.

So it must be working.  Let us try booting

Yep, Cromix 172 XXU was read from the single 1.2MB floppy disk and the Operating System started.

All is well!

Now Remember

True System Builders always observe the rule:

Never put the case lid back on until everything is working. :-)

Otherwise you will spook it and things are bound to go wrong.

All in all the system is back up, running all peripherals on PC power.  Good for the next 20 years I reckon.

And Now

Snap: The Power