PDA

View Full Version : Model 25 ibm ps/2 box external power supply idea for an internal hdd



kiyotewolf
May 21st, 2011, 12:54 PM
Snipped from a private msg.
Names withheld for privacy.

Quoted

"i've got an ISA drive controller i could throw in"


What you can do, is, adapt the existing OEM model specific iteration
of the IDE header, and adapt out +5, -5, +12, -12 voltages, to hook up
a hard drive, then use the ISA controller with an 8-bit slot.

The ISA controller uses modern ribbon cable, to connect the hard drive
to the computer.

YES THE MODEL 25 has an IDE port, but it is PROPRIETARY. It's like
Power-Over-Ethernet, where the unused pairs carry power to a remote
device, IBM made a proprietary power supply scheme, where they used
about 4 ribbon cable wires per power rail (a power rail is a wire from
the power supply, it also means it's the source voltage, whatever that
might be, so it could be a power rail of negative five volts, or of
five positive volts, or of 12 negative volts, or of 12 positive
volts), so that's 12 wires off the existing IDE on the ribbon cable
(this is a guesstimation based on photos of someone who modded a hard
drive INTO a PS/2 Model 25).

SO!

I have an alternative.

You will love this.

If you plug in your hard drive to the Model 25, it will blow your hard
drive, and ruin the computer as well, because it's carrying HIGH
CURRENT POWER to the drive, along the WRONG PINS.

So!

Get the ISA controller card, (if I had the ISA card, I wouldn't have
the want to get rid of the Model 25 in the first place, I would've
modded in a hard drive already, and used it as a talking computer with
SPEECH.COM which REQUIRES 4.77mHz speeds, to talk correctly), then do
this.

Find the ground plane between the Model 25 and a seperate EXTERNAL
computer power supply.

If you can connect a 2nd power supply between the Model 25, and the
Hard Drive, you can provide the data bus via the ISA 8-BIT CARD, and
provide the power, via an external junk computer, stuffed in a box.

BUT!!!!!

You must do THIS, to make that idea work, as long as it WILL work.
This is THEORETICAL, and SHOULD WORK, without killing the computer, (I
hope).

Connect the BLACK lead of the external power supply AND THE GROUND OF
IT, meaning the casing should have a wire screwed from it, to the
casing of the Model 25.

There needs to be a COMPLETE LOOP, of current, between the Model 25,
and the EXTERNAL power supply, if the power going from the external
computer supply, will feed the power needs of the INTERNAL hard drive.

If you simply make a long four-pin wire, that connects from the
external, snaking inside the Model 25, and leave it there, if the
power supply and the Model 25 cases touch, there will be an ADVERSE
current flow, due to an imbalance in current flow.

IF YOU CONNECT THE BLACK OF THE EXTERNAL TO THE BLACK OF THE INTERNAL,
AND TIE THE GROUND PLANES BETWEEN THE INTERNAL AND THE EXTERNAL ADD-ON
EXPANSION BOX, THEN YOU WILL HAVE PROPER CURRENT FLOW, AND THE POWER
SUPPLY WILL BE ABLE TO RUN THE HARD DRIVE WITHOUT HAVING AN ELECTRICAL
FAULT, FAILURE, OR OTHERWISE POWER FLOWING THE WRONG WAY, AND IT
SHORTING OUT AND DESTROYING EVERYTHING WITH RAMPANT UNWANTED CURRENTS.

Also. One more thing.

Tie the power cables together of the EXTERNAL and the INTERNAL power supplies.

If the pins of the internal power supply feeding the AC input plug are
reversed, compared to the external power supply, you WILL, (and not
may you WILL), GET ADVERSE CURRENT FLOW.

This is a problem with poor circuit design, but is handled, if you
splice two normal PC power cables together, so that it functions like
one device, with ONE SINGLE POWER PLUG. THIS IS DEAD HONEST ESSENTIAL
FOR MY IDEA HOWEVER THEORHETICAL TO WORK BECAUSE IF YOU KEEP THE
INTERNAL AND EXTERNAL POWER SUPPLIES ON SEPERATE WIRES, AND YOU USE A
3 PRONG TO 2 PRONG ADAPTOR, AND REVERSE THE PLUGS POLARITY ON TWO
DIFFERENT SIDES OF AN EXTENSION CORD, YOUR GROUND PLANE WILL BE IN
OPPOSITE PHASE OF YOUR OTHER GROUND PLANE, AND YOU WILL HAVE 60 HZ
FEEDBACK BETWEEN GROUND PLANES, OR WORSE, 120V AC BETWEEN GROUND
PLANES, THEREBY EXPLODING AND DESTORYING THE ENTIRE PROJECT.

I only detail all the gory mess of a failure, because i want you to be aware.

Adding a hard drive to a Model 25 is a HUGE UNDERTAKING, and if you
can get assistance, modify the proprietary IDE port to provide
INTERNAL power to your hard drive.

If you are not ribbon cable savvy, like I am not, then you would shy
away from such risky ideas, BUT if you are power cable handy, like I
am, my idea, however risky it is, on it's own level, is something a
ribbon - cable non-savvy person might try, as a last resort.

if you want me to do a tutorial video on how to do my idea of powering
the internal via external means, I will put together a video show
program, of what I just wrote.



:M

Unquote.



Does this make sense to you guys, my idea, of trying the ground planes together to provide more +5, +12 levels to something new?

I'm thinking along the lines of the Power Of Tower which was a much touted Expansion box for the Tandy 1000 HX, which I was drooling over and still do, well, ever since I saw it advertise in 1989.



:M

Chuck(G)
May 21st, 2011, 02:20 PM
Sounds complicated. Do you have a free ISA slot? It might be simplest to pick up the XTIDE controller, a CF to IDE adapter and a CF card, which can be powered from the XTIDE traces (the V2 PCBs have a header for CF power). No fooling around with power cables, power supply ratings. It's quiet and fast and generates little heat.

Has anyone run an XTIDE card on a Model 25 yet?

lutiana
May 21st, 2011, 02:24 PM
I tried my XT IDE in my model 30-8086 and I could not get it to boot with the ISA MFM controller installed. But that was as far as I got, plus it was an old BIOS on the thing so I would not call this definitive at all.