8087 on DEC Rainbow 100A

[bsdimp]

Greetings,

I recently purchased a PC1XX-AK on ebay. It was billed as a 8087 board, but that was just what was printed on the board. There's no 8087 on that board. It's just a memory adapter. Which is cool, as it lets me have 832k on my 100A now.

Has anybody had luck retrofitting a 8087 onto such a board? It looks like there's room to solder in a socket and put an 8087 there. There's also a bunch of other unpopulated pads as well for reasons unknown, so I thought I'd ask before embarking on board destruction.

I'm aware of the PC1XX-EA that's for the 100B that has a 8087 on it. I've been looking for one of these for years since I accidentally missed the last one that came up on ebay.

Warner

 

[saipan59]

Greetings,

I recently purchased a PC1XX-AK on ebay. It was billed as a 8087 board, but that was just what was printed on the board. There's no 8087 on that board. It's just a memory adapter. Which is cool, as it lets me have 832k on my 100A now.

Has anybody had luck retrofitting a 8087 onto such a board? It looks like there's room to solder in a socket and put an 8087 there. There's also a bunch of other unpopulated pads as well for reasons unknown, so I thought I'd ask before embarking on board destruction.

I'm aware of the PC1XX-EA that's for the 100B that has a 8087 on it. I've been looking for one of these for years since I accidentally missed the last one that came up on ebay.

Warner

If you're talking about adding an 8087 to a board that wasn't designed to have it, I think there's no way that it's worth the trouble, and probability of success seems low, unless you are quite an expert at early x86 design...
But I could be wrong ;-) .

Pete

 

[Terry Kennedy]

If you're talking about adding an 8087 to a board that wasn't designed to have it, I think there's no way that it's worth the trouble, and probability of success seems low, unless you are quite an expert at early x86 design...
But I could be wrong ;-)

I read the OP as saying that there was PCB etching for an 8087, but it wasn't populated on his board. DEC was quite fond of using the same board for a variety of configurations - memory boards that could take 4K or 16K chips, parity or not, and so on; multifunction bootstrap / terminator / memory refresh / kitchen sink boards in a variety of configurations.

If this is one of those, a combination of looking an an original IBM PC Technical Reference (to see how IBM wired the 8087 to the 8088) and reasonable-resolution pictures (if available) of boards with the 8087 option installed might provide enough information to add it to this board.

 

[bsdimp]

Followup two years later: I got my 8087 board via winning a DEC Rainbow that was being sold as is and while the main board was broken in ways that are resisting repair, it did have both a 8087 board and a 1MB board from suitable solutions in it... I did look into populating the chips in the original board and saipan59 was right: it was going to be a huge hassle....

 

[na103]

Followup two years later: I got my 8087 board via winning a DEC Rainbow that was being sold as is and while the main board was broken in ways that are resisting repair, it did have both a 8087 board and a 1MB board from suitable solutions in it... I did look into populating the chips in the original board and saipan59 was right: it was going to be a huge hassle....

Hi bsdimp,
from what i read here should you have an 8087 card like this?


this is the only half picture I could find on the Internet.

I'd like to rebuild it like I did with the memory expansion and graphics card here

https://forum.vcfed.org/index.php?threads/rainbow-100-graphic-card.1237512/

https://forum.vcfed.org/index.php?threads/rainbow-100b-memory-extension-board.1234350/

Would you like to collaborate with me by sending me some hi-res images now and in the future do some measurements with the multimeter?

Thank you
Nicola

 

[alitel]

Hi Nicola,
Resurrecting an old thread here -- I just had it explained to me how this works on a 100A -- I am EXTREMELY keen to acquire one of these 8087 adapter boards, so am now on the hunt. If I do find one, I'd be more than happy to provide any information you wish if you still want to pursue a modern rebuild (which I think would be fantastic -- the only thing AFAIK that holds a 100A back anymore is the memory limit (though I could be wrong).

Cheers, A

 

[N. Brown]

DEC part number PC1XX-AK is really a Memory Expansion Adapter with the unused option for a 8087 Numeric Co processor.
Dec PCB number 50-16534-01 is both the Memory Expansion Adapter with the 8087 Numeric Co processor installed .
..
These cards still come up for sale on Ebay.com at times.

 

[N. Brown]

Hi Nicola,
Resurrecting an old thread here -- I just had it explained to me how this works on a 100A -- I am EXTREMELY keen to acquire one of these 8087 adapter boards, so am now on the hunt. If I do find one, I'd be more than happy to provide any information you wish if you still want to pursue a modern rebuild (which I think would be fantastic -- the only thing AFAIK that holds a 100A back anymore is the memory limit (though I could be wrong).

Cheers, A

If you can not get a hold of one of the following RB100 expansion cards
DEC part number PC1XX-AK is really a Memory Expansion Adapter with the unused option for a 8087 Numeric Co processor.
Dec PCB number 50-16534-01 is both the Memory Expansion Adapter with the 8087 Numeric Co processor installed .
..
It is possible to modify a RAINBOW 100B Memory expansion card to work with the 100A and 100+ models, but this will require cutting a couple of circuit traces and rewiring a couple of new jumper leads.
To do this modification there would be a lot of data that I would have to re enter on to this forum for a archive.

 

[alitel]

Thank you also for this! I do see an expired listing on ebay for one of these. I will add the part numbers to my ebay saved searches!

Cheers! A

 

[N. Brown]

Greetings,

I recently purchased a PC1XX-AK on ebay. It was billed as a 8087 board, but that was just what was printed on the board. There's no 8087 on that board. It's just a memory adapter. Which is cool, as it lets me have 832k on my 100A now.

Has anybody had luck retrofitting a 8087 onto such a board? It looks like there's room to solder in a socket and put an 8087 there. There's also a bunch of other unpopulated pads as well for reasons unknown, so I thought I'd ask before embarking on board destruction.

I'm aware of the PC1XX-EA that's for the 100B that has a 8087 on it. I've been looking for one of these for years since I accidentally missed the last one that came up on ebay.

Warner

Yes you can retrofit the Pc1XX-AK to have a 8097 numeric coprocessor on it, but that in theory will change its part number. To do this change I recommend a good disordering station to do it.
AS far as a parts list of components that is need, if you can read the component values and the semiconductor part numbers off the pictures I have uploaded to this forum that should survives.
..
As far as the 8087 Numeric processor option we used a different one when we where refurbishing the Dec. RB100 for export sales, it was cheaper and quicker for us to get.
So for any custom PLA used we likely no longer have the code for them.