Compaq Deskpro 286 model 2550 - problems with all memory boards

[dhau]

Hi folks,

I wonder if it is a common problem that none of EMS/XMS boards seem to work in Compaq Deskpro 286 model 2550 (8MHz).

I tried Intel Above Board AT, Intel Above Board Plus 8 and AST Rampage 286. Intel boards stop PC from POSTing. With AST board, Deskpro POSTs and boots, but ramp.com doesn't detect the board...

Any advise? Model 2550 is very similar in spec to IBM PC AT 5170, and all my memory boards work fine in 5170.

 

[jafir]

Have you run the setup disk for the compaq to tell if you’ve got the extra memory installed?

For the AST cards, what version of superpak disk are you using?

How much RAM does the deskpro have onboard? Is it 512k like a 5170 or 640k like the older 8086 deskpro? That may change where you need to set the starting amount of memory on the cards.

 

[dhau]

Thank you for your reply!

This Deskpro has both BIOS and memory on the Compaq Magnum 16-bit isa card. It has 128KB of base ram soldered in and another 1MB of memory in 4x9 41256 chips, so the total memory is 128+1024=1152KB. I had to remove second megabyte of memory, because it was conflicting with ROM on network card.

I should also mention that is has Realtek 8019 ISA network card with 16KB ROM @ C800h with XT Universal BIOS for AT r602. This is how I can boot from a 2GB CF card. May be the network card conflicts with extended/expanded memory boards.

Update: I apologize, I should've tried it first. The slot I used was never used before, so probably had some oxidation. After I moved the memory card to another slot, it worked. I then moved it back and inserted/removed the board several times to clean up the contact pads and then it started working even in the slot where it didn't work before.

 

[dhamilton]

Hello! I was wondering if you could help me out. I have one of these "magnum" Compaq boards and I am trying to find one of these memory boards. Would it be possible for you to take a picture of your card? I have the part number, but it would be really helpful to have a picture of one to show someone looking for it.

I appreciate your help!

 

[dhau]

Here it is

 

[dhamilton]

Thank you! How well is your system running? If you ever want to part with it, let me know. Or if you're interested in the newer 286 board I can help out.

 

[dhau]

My Compaq Deskpro 286 model 2550 runs very well. I ordered a Compaq VGA card from 1987 with PVGA1A chipset. Hope it'll work. I got one before and it was doa.

My PC has original Compaq multi-io card: parallel, serial, floppy and IDE controllers. It uses Magnum card for 2MB + 128KB memory. I also installed Intel Above Board AT for 2MB EMS memory. And a Sound Blaster 16. No problems with it, runs very stable, I did upgrade ROM to J.2 version using two Winbond 27c257 eeprom chips.

I got an original Compaq Deskpro 5.25" DS/DD floppy drive and a modernish 3.5" black floppy.

I like Compaq computers from 1980s, so I'll keep it for as long as my living conditions will allow it. I also have a couple of Compaq Portables (8088), one Portable II (286 @ 8MHz), two Deskpro (8086), all with original Compaq cards in them. I do hope to buy an original Compaq Enhanced keyboard some day, but I'm in no rush.

 

[dhamilton]

Nice! I've been trying to assemble (as close to stock as possible), the Compaq flagship desktop machines from 1984, 1985, and 1986. These years are when they introduced their first 8088, 286, and 386 machines.

I've had mixed luck so far. I have a Deskpro (8088), a Deskpro 286 (2550), and a Deskpro 286 (2551). The original boards in these had sadly been mostly replaced by the time I got them. My mission is to restore these to original stock as best I can.

Original boards in these computers are important because in some cases there are compatibility issues in some instances with generic cards. For example, the Deskpro 8088 expects a printer port on 03B0h, (not 0378h), and will throw a 401 error on boot-up if it doesn't detect one. The 10/20 MB tape drives included in these old machines don't seem to work unless they are connected to a Compaq floppy controller.

Besides the original monochrome adapter, which I have two or three of, I don't have any original Compaq display cards. I did however get lucky and find a Compaq EGA monitor, which would match up well with the Deskpro 286.

I have one working Compaq Floppy/Winchester controller. It had a dead short in it when I got it. A capacitor had shorted (but wouldn't blow). I replaced the cap and it now works.

I'm in the process of teaching myself how to do basic repair of these things, like troubleshooting dead boards, etc. That part alone is a fun hobby unto itself. Do you still have the display card that was DOA? It's very possible it can be repaired. The tantalum caps on these things are notorious for shorting.

I'll keep my eye out for a keyboard.