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XT clone built from ebay components

J

jh1523

Experienced Member
Joined
Jan 15, 2009
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298
Location
coastal New England
So I found recently on ebay a nice combo of a XT clone motherboard (very similar but not exactly the same as this one http://www.uncreativelabs.de/th99/m/U-Z/33657.htm) which is completely populated with 640K RAM and has 5 out of 8 BIOS sockets filled with 2764 chips (one labeled BIOS and the others numbered 1-4) and two 8-bit ISA cards. One of the cards is a CGA adapter and the other one is a multifunction 384K RAM (which can only be used to fill conventional memory, i.e. useless in this motherboard) and RTC. You can see pics of the motherboard here
http://i.ebayimg.com/00/s/OTAwWDE2MDA=/z/dhoAAOSw9N1VmL9t/$_57.JPG
http://i.ebayimg.com/00/s/MTYwMFg5MDA=/z/6XsAAOSw~gRVmL92/$_57.JPG
http://i.ebayimg.com/00/s/MTYwMFg5MDA=/z/O78AAOSwT6pVmL9-/$_57.JPG
http://i.ebayimg.com/00/s/OTAwWDE2MDA=/z/DAsAAOSwDNdVmL-E/$_57.JPG
http://i.ebayimg.com/00/s/OTAwWDE2MDA=/z/5usAAOSwPcVVmL-M/$_57.JPG
http://i.ebayimg.com/00/s/MTYwMFg5MDA=/z/01MAAOSwjVVVmNGx/$_57.JPG
http://i.ebayimg.com/00/s/MTYwMFg5MDA=/z/dUsAAOSw9N1VmNHF/$_57.JPG
http://i.ebayimg.com/00/s/MTYwMFg5MDA=/z/-I0AAOSwDNdVmNHL/$_57.JPG

The mobo and cards are in pristine, almost unused condition - and they come with the original manuals too, including complete schematics and for the video card programming reference for the registers. :)

I've put them together and it works beautifully so far. My problem now is that I don't have a floppy interface that works with it. I tried all of my ISA multi-IO cards, which are 16-bit. The mobo recognizes the serial, parallel and game ports on them - but not the floppy or the HDD interfaces. Thus I haven't been able to get an OS running on it yet. When it doesn't find a floppy it defaults to the ROM Basic.

I do have a lo-tech ISA CF adapter (rev.2, not the latest 2b) which I use with a 6GB microdrive on a few 386 and 486 machines - it has DOS 5 installed - but in this machine it just causes it to hang and not boot. I think I may have to recompile the XT IDE universal bios with only basic XT support and no 286/386 opcodes, because I think that may be the problem. And I just realized that when I get the universal bios recompiled I will have no way to transfer it to a 386 or a 486 where I can flash it because I lost my USB FDD and I won't be able to write a floppy from my laptop. :( Crazy idea, but I may have to dig out my old camera which uses CF for storage, attach it to the laptop and see if I can use it to write to the microdrive...

Stay tuned.
 
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It's pretty unusual to have so many ROMs installed. Try unplugging all of them except the ROM BIOS and try your controllers again. Perhaps they are conflicting.
 
Very nice generic board.

Is it sometimes possible to use the floppy controller of a 16-bit ISA FDD/HDD card on an 8-bit system. But you will only be able to access 360K/720K disks unless you add a special BIOS, or install a driver after booting. The hard disk parts won't work. So if you have a USB 3.5" floppy drive, make sure it can handle 720K disks.

What kind of motherboard BIOS does it say it has? It is kind of odd to have more than one chip unless it has a pirated IBM BIOS with basic. :)
 
Looks like a great build!

I have one of those motherboards myself but I stole some IC's from it years ago (for another project...). Unfortunately I don't know which IC's to replace where as back in the day I really didn't care about the board.

It would be fantastic if you could take some Hi-Res pictures of the entire motherboard itself so I can read the IC part numbers. I hope someday to see if I can get this motherboard working again; although I still need to find a BIOS for it.
 
3pcedev said:
Looks like a great build!

I have one of those motherboards myself but I stole some IC's from it years ago (for another project...). Unfortunately I don't know which IC's to replace where as back in the day I really didn't care about the board.

It would be fantastic if you could take some Hi-Res pictures of the entire motherboard itself so I can read the IC part numbers. I hope someday to see if I can get this motherboard working again; although I still need to find a BIOS for it.
Click to expand...

I'll be happy to post hi-res pictures, as well as dump images of the bios chips.

Here are hi-res photos (20MP). I think you can read every chip between the two, let me know if these work for you.

https://dl.dropboxusercontent.com/u/107843342/xt/IMG_0037.jpg
https://dl.dropboxusercontent.com/u/107843342/xt/IMG_0038.jpg
 
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Here's a dump of the main bios chip, the one marked "SID v4.1 BIOS"

I made both a .bin and a .hex image, they're both inside the archive.
 

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jh1523 said:
Then when it fails reading from FDD falls back to Basic.
Click to expand...
Per what SomeGuy wrote, I expect that with a 16-bit floppy controller, you will be able to boot from a 720K sized 3.5" boot diskette.
An image of such a boot diskette (created using WinImage) is in the STEP 2 section of [here].
 
Those basic ROMS are identical to the IBM PC basic v1.10. I'm not aware that IBM or MS licensed those, but obviously some third party BIOSes could accept them.

The first ROM is a generic XT clone BIOS. It looks to be completely rebranded by the OEM, so not sure exactly who wrote this one. The "Anonymous" PC bios used by MESS is a newer version of the same thing.

BTW, that first "ZIP" file was actually a 7-zip, that used their new beta's compression that not all other clients support.
 
SomeGuy said:
BTW, that first "ZIP" file was actually a 7-zip, that used their new beta's compression that not all other clients support.
Click to expand...

Yeah, I made it a 7zip but then the forum software didn't want to accept it with a 7z extension so I just renamed it instead of compressing it again. :p

Also: yes, it looks like the "pcxt.rom" file is almost identical except for the ... trademark. :) I wonder if I burned that file in an EPROM and plugged it in the board, would it work? Hmmm...
And the "turbo 3.10.bin" seems to be an earlier version of the two. :p
 
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jh1523 said:
I wonder if I burned that file in an EPROM and plugged it in the board, would it work? Hmmm...
Click to expand...
It should. Your board looks to be a fairly standard ERSO style clone, which itself is a very generic XT clone, which is what MESS emulates. In general, you can interchange the BIOS between these kinds of boards without much issue. In fact, if it were me, I would probably plop a Phoenix BIOS in there, as that often seems to increase software compatiblity (I always had issues with the DTK BIOSes).
 
That board is very similar to an XT board I have, which also has the IBM Basic Roms (labeled in the pic below)
 

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As an experiment I programmed an EPROM with the Phoenix 2.51 BIOS from http://www.minuszerodegrees.net/xt_clone_bios/xt_clone_bios.htm and used it in the X'golden motherboard. It works, but stalls at "cannot find boot disk" and doesn't go to Basic. I guess I won't know if it's fully functional until I find a way to attach a boot device.

(FWIW I didn't have any 2764 chips so I used a 27256 and programmed it with 4 copies of the BIOS concatenated)
 
mikey99, do you happen to know if your BIOS is also the same "Special Integrated Designs Co" OEM?

I'm wondering precisely what the original source was. A quick Google search doesn't turn up much of anything for Special Integrated Designs. But there were many, many tiny outfits that did custom ERSO board based systems.

It looks like this outfit must have regularly included IBM Basic ROMS on their boards.

Also, I like how all of the chips are socketed. Very easy to fix. Most ERSO styles boards don't use sockets for the logic chips.
 
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