29 Aug
2025
29 Aug
'25
7:41 a.m.
On 8/29/2025 10:30 AM, Tony Duell wrote:
Apart from slot 8 in an IBM PC/XT motherboard (which this is), all
slots are the same. The ordering I gave is simply how the machine was
shipped from IBM, it makes sense as it gives the neatest run of video
and floppy cables.
FWIW, my 5155 has the following cards :
1 CGA video
2 Data Acquisition/Control
3 Floppy controller
4 and 5 Async serial (modified so you can use either RS232 or current
loop without opening the case)
6 and 7 Parallel printer (modified to have bidirectional data lines)
I've also done the motherboard mod to have 640k RAM there
OK, Slot 8 is not convenient so it can remain empty. I'll
figure out an order based on the cabling.
Oh, based on experience I expect it will work fine as long as I
don't leave it turned off for 20 years again. :-)
If the floppy drive is the orginal Qumetrak then there are little
plastic spacers on the screws to fit into the recesses on the drive
chassis casting. One of mine was missing so I milled a replacement
from plastic block
It's TEAC 55. Only one of those spacers was there.
Well I do. To the extent that I bought all the Techrefs from IBM many
years ago and have a shelf of them upstairs. I've also downloaded the
bitsavers ones of course. Along with manuals for literally hundreds of
other machines. Maybe you can find a failed component on your own but
I am stupid enough to need the schematics.
I have never been able to learn how to do anything from a video, for
me it's the most ridiculous way to present such information. And
there's so much misinformation on the web (in all fields) that I
prefer to start from the original manuals rather than somebody's
version of whatever
Sorry, I was just trying to be humorous. I have piles of paper manuals
for most of my computers. As for failed components, I have never and
would never waste time trying that on a PC class machine. Now, on a
PDP or VAX.... Still have an oscilloscope.
bill
On Fri, Aug 29, 2025 at 2:26 PM Bill Gunshannon via
cctalk
<cctalk(a)classiccmp.org> wrote:
Just a comment that I found it interesting. Surprised there
isn't a lot of noise on the screen.
On 8/28/2025 3:03 PM, Tony Duell wrote:
Not in the origiinal IBM version. On Thu, Aug 28, 2025 at 7:46 PM Bill Gunshannon
via cctalk
<cctalk(a)classiccmp.org> wrote:
Interesting. Not coax.
On 8/28/2025 1:07 PM, Tony Duell wrote:
> On Thu, Aug 28, 2025 at 5:51 PM Bill Gunshannon via cctalk
> <cctalk(a)classiccmp.org> wrote:
>>
>>
>> I finally got the missing keyboard and now it is time to try
>> and revive it.
>
> I restored one some months back. Mine is 100% IBM boards and options....
>
> The portablePC has a normal XT motherboard in it. The standard video
> board is the CGA one, with the composite output (on the 4 pin
> connector originally designed for an RF modulator) feeding the
> internal amber moniitor. This is actually a Zenith unit.
That explains the weird little cable stretching over some of the boards
and getting in the way. :-)
It's normally yellow and black twisted pair.
As standard, the CGA card goes in slot 1, closest to the PSU. Floppy
controller in slot 3. This leaves slot 2 as an empty full-length slot
and slots 4-7 as half-length ones. Slot 8 is not really useable. Being
an XT motherboard, the card there has to assert the buffer enable pin
on reads. The only IBM card that will do that is the async serial one.
And it's about 1/4" too long to fit, it fouls the power connectors on
the drives.
More interesting info. I was not aware of there being any priorities
on the IBM PC bus. I thought all the slots were the same. At least in the past when I last worked with PC's at
the hardware level (a
really long time ago when they were new) I never saw any needed
ordering of the cards.
Here's mine, satrtng from the PSU:
Slot 1: That CIL thing (now that I have booted without it I think
it was an interface to some weird lab device,
They had similar interfaces in their Apple ]['s
as well.)
Slot 2: Memory
Slot 3: Floppy ( a long card )
That may be the original IBM card
Slot 4: HD Controller (WDX-GEN)
Slot 5: Video-Serial-Paralel
Cerrtainly not IBM!
Slot 6: Empty
Slot 7: Empty
Slot 8: Empty
Recommended ordering?
Whatever fits in the case and lets the cables run neatly. > No idea yet as it is buried in the system
below the floppy. But I
> plan on pulling it out as soon as I figure out the mounting scheme
> for the disks.
OK. I took it all apart. Miniscribe disk. With it out I hooked it up to an ext5ra PSU I had and toggled the power
on and off a bunch
of times. It finally spun up and the blinky LED is not longer blinky.
It may work for the moment. I'd grab any interesting data off it ASAP though.
I seem to remember you need a 5.5mm or 7/32" spanner and nutdriver to
do that. You take off the earthing bracket on the right hand side of
the drives towards the rear, then loose the other 3 screws on each
drive and slide them out backwards.
Ended out having to take the screws all the way out so I could
wiggle them a lot. Very snug fit, especially the fascia.
There are some useful manuals on bitsavers. The Technical Reference
for the PC/XT and portablePC gives the motherboard schematic and BIOS
source. The Options and Adapters volume 1 gives the schemaitcs for the
drives and monitor. And volume 2 gives the CGA and floppy controller
schematics (and lots of others).
Pfft. Who needs manuals when you have google and youTube. :-)