CPU Shack: IBM 64-256K PC/XT Mainboard - SOLD

[CPUShack]

Here is a nice IBM 6320152 PC/XT Mainboard, with a 1983 dated P8088

Fully populated Memory (256K)

Unknown if it works, but looks nice

$25 and its yours

[CPUShack]

Make me an offer

[debs3759]

I would make an offer, but without knowing if it works it's too much risk

I need a working 808x motherboard

[stamasd]

I offer $16 due to unknown working condition.

[CPUShack]

Sold, let me know if it works

[stamasd]

Can you do me a favor? I'd appreciate if you could post a close-up picture of the chip marked U44 on the motherboard, or at least write down the markings on the chip. I can't read it from the picture above, even zoomed. It's the socketed chip located right below the large AMD 8255 in the picture.

It should be a bipolar PROM 256x4, but I want to know exactly which one. I've seen versions of this motherboard use 24S10, 82S129 and 74S287 chips.

(depending on which it is, I may be able to replace it with one that has modified data and expand the memory on the motherboard from 256k to 640k, or even 1024k)

[CPUShack]

TBP24S10N (TI)

[stamasd]

Thanks. So it's the original chip as in the IBM docs. Should be easy to replace.
(but not with the same - I'll fit an EEPROM instead; I don't trust ebay sellers for "NOS" OTPROMs that are 30+ years old)

[CPUShack]

[stamasd]

Yeah. You need an adapter of course. But it's much safer than buying at random PROMs that may or may not be blank, and are quite rare and expensive too. It's done routinely to keep old arcade cabinets working.

[stamasd]

Very late update on this motherboard.
I've managed to make it work.
It had a lot of corrosion around the CPU and clock chip, as well as the NPU socket and even some of the PSU connector. Some of the CPU pins were so corroded that 4 of them broke off when I pulled it from the socket.
I don't know how that corrosion happened there, but I cleaned it up nicely. Soldered back pins on the CPU and for protection I inserted it into a 40pin socket to act as an interposer.
Next issue was the trimmer capacitor in series with the clockgen crystal was broken. I replaced that of course.
Next issue was U19 (one of the 2 BIOS chips) was bad, only reading blank. I replaced U18 and U19 with a custom BIOS burned into EEPROM chips.
Next issue was when powering up, one of the tantalum capacitors (the one on the 12V rail) exploded, as these are known to do. I replaced the capacitors on the +12V and -12V rails with ceramic MLCC capacitors.
Next issue - well not an issue, but there by design - board is 64-256K and I wanted the full 640K so I did the appropriate mod.
With all the above the board works now.

Some pics:

CPU with corrosion and broken pins.


Repaired CPU, inserted in cleaned up socket via 40pin interposer. And new custom BIOS chips, and 640k mod also visible.


Blown capacitor

After fixing all of the above, the board now works correctly.

[Mearas]

Thx for the late reply.

[karman]

Basic on ROM! That's cool. I Thought this board would boot from floppy or hard disk.

[H3nrik V!]

Great when old posts are revived with succes stories!

[Marcin]

Old batteries make disaster from top to bottom of board and I was suprised when even last ISA slot can have corroded pins. Above case was on level hard but thankfuly you recovered it