Image Map Image Map
Page 1 of 2 12 LastLast
Results 1 to 10 of 11

Thread: Compaq Deskpro 386/25e Memory Expansion

  1. #1
    Join Date
    Apr 2011
    Location
    NYC, New York
    Posts
    18

    Default Compaq Deskpro 386/25e Memory Expansion

    Hello everyone,

    I have a Compaq Deskpro 386/25e that I would like to add more memory to. It has 4mb currently installed (I'm guessing the module on the mainboard), and based on this thread here from recently, I have a few options for installing the memory.

    These units have what looks like a proprietary connector for memory expansion, and from what I understand from the thread, I can install either a 1mb expansion card or a 4mb expansion card with the ability to add more modules to the cards.

    So I found and purchased this Kingston KTC-4000E module thinking it was a 4mb base card with the option to add 2 more 4mb modules which is why the listing is shown as 4mb-12mb expansion. I'm guessing I misunderstood something...

    When I installed the card, the computer booted up and began testing the memory. Usually it stops at 4096kb, however with the card installs, it reaches 4032kb, the screen goes blank and the computer beeps twice while the floppy drives do their initialization sounds. Then that's it, the computer does nothing else. Numlock is still responsive.

    I removed all other ISA cards except for the memory expansion card and attempted to boot the system but the same thing happened.

    Did I do something wrong? Is there a jumper I'm not aware of? Or am I screwed and I bought the wrong card. I figured that since it had the proprietary connector, it was compatible but that may have been an incorrect assumption thinking back.

    Here are some pics of motherboard and the Kingston card in case it can help you guys.

    DSC_0109.jpg
    DSC_0110 (1).jpg
    s-l1600.jpg

    I found these two cards on eBay, not sure if they would be compatible or not:

    https://www.ebay.com/itm/NEW-NOS-COM...S/321683980127

    https://www.ebay.com/itm/COMPAQ-1125...5/112370657271

    Thanks for looking and for your time

    Mike

  2. #2
    Join Date
    Mar 2017
    Location
    New Jersey, USA
    Posts
    463

    Default

    The Deskpro 386/25e is slightly different from the Deskpro 386/25 so not everything in that other thread applies here.

    First, the 386/25e has space for a memory module on the system board. I think it is assumed you will always have this populated with a 4MB module (all memory configurations shown in the Compaq Service QuickRef start this way). You can then add either a 4MB or a 1MB board, and each board has 2 sockets that will take 4MB or 1MB modules. While you can add 4MB modules to the 1MB board and vice-versa, it appears that if you add 2 modules to a board they must both be the same size. Each memory board has only 2 positions for add-on modules (unlike the 386/25 boards which allow 3 additional modules).

    All that said, it looks like you got the right board. I'm not sure why it's not working. There's nothing in the QuickRef about any jumper or switch settings, it should just work.

    Code:
    1MB expansion board Assembly 000960 Spares # 112518-001
    4MB expansion board Assembly 000963 Spares # 112517-001
    1MB memory module Spares # 113225-001
    4MB memory module Spares # 113226-001
    Note that while the memory boards have different spares numbers, the modules that go on to the board are the same ones used for the 386/25. So those at least should be interchangeable.

    The 2 ebay links look like the wrong thing, those are for the Deskpro 386s which was a 16-bit machine (386SX CPU)
    Last edited by kgober; November 15th, 2018 at 01:57 PM.

  3. #3
    Join Date
    Apr 2011
    Location
    NYC, New York
    Posts
    18

    Default

    Hey thanks for the reply. I've been pulling my hair out over this issue all week. So I contacted the seller and he agreed to send me another older style KTC-4000E which is the Kingston equivalent to 112517-001. We were thinking that maybe since the newer revision has higher density memory chips, it could be causing an issue. However that didn't work. The same problem persisted.

    He also sent me an actual 1MB, 112518-001 Compaq board, and that also exhibits the same behavior.

    I have filmed the problem hoping it can help

    https://photos.app.goo.gl/CZJBsHnU5NMPn5hp8

    You can here the system beep as if there is an issue, but the screen goes blank and doesn't respond to any key presses.

    I'm really at a loss here. Any help would be greatly appreciated.

    Thanks

  4. #4
    Join Date
    Apr 2011
    Location
    NYC, New York
    Posts
    18

    Default Big Update

    So just an update, I've actually made some progress. When the screen goes blank and I hear the two beeps, I hit F1 thinking the system was experiencing an error and it was prompting me to hit F1 to continue. I was actually right. The screen comes back on and MS-DOS loads. I startup 3.1, and when I go into control panel, I get "insufficient memory to open this application". So I exited and put the Compaq setup disk in to see if I can figure out what's going on. Then the fun began...

    Here's what I'm shown before setup loads:

    DSC_0138.jpg
    Followed by:
    DSC_0139.jpg
    Followed by:
    DSC_0140.jpg

    Once in setup, the BIOS detects the memory expansion board, and reports the correct amount of memory:

    DSC_0142.jpg

    In this case, I'm using the 1MB Compaq expansion board. The BIOS always shows the correct amount (if I'm using the 1MB Compaq, or both 4MB Kingston boards).

    I then ran the diagnostics on the setup disk, and here's what I get (for all 3 boards):

    DSC_0135.jpg
    And...
    DSC_0133.jpg


    When I run MEM in DOS, here's what I get:

    DSC_0132.jpg

    And finally, like I said before, once in Windows 3.1, all I get is this:

    DSC_0127.jpg

    So once again, I'm not really sure where to go from here. It does this for all 3 memory boards. I have a hard time believing they're all bad. Is there a setting in the BIOS that I'm missing that is used in this situation?

    The only BIOS setting I see for memory is this:

    DSC_0141.jpg

    Don't really want to mess with the advanced system options.

    What exactly is a parity error? I'm really hoping my motherboard is bad.

    Once again, any help is much appreciated. Thanks for your time.

  5. #5
    Join Date
    Mar 2017
    Location
    New Jersey, USA
    Posts
    463

    Default

    The original IBM PC, and many of the systems that followed it, used 9-bit-wide memory. Generally this was done by using 9 chips. For example. using 9 64-kilobit chips, you would end up with 64-kilobytes of 9-bit memory. Since the 8088 used 8-bit memory, that 9th bit was used as a parity bit, in order to detect memory errors.

    Parity is a way to detect errors by including an extra bit that reports whether the number of other bits 'set' is even or odd. If an 8-bit value has an even number of bits set, the parity bit will be set one way, and if there are an odd number of bits set, the parity bit will be set the other way. Now if any single bit fails and reports the wrong value, this will show up as a parity error.

    It seems unlikely that you have 3 bad memory boards so I'm afraid the issue is likely with your system board. It could be a relatively minor thing like an issue with the socket (maybe a damaged contact, or a failed solder connection) or it might be something basically unfixable like a failure in a custom Compaq memory controller chip. I don't know enough in this area to be able to give particularly detailed advice about how to proceed.

    It might be that the best path is to be happy with a 4MB DOS system, and get yourself a 486 for Windows 3.x.

  6. #6
    Join Date
    Apr 2011
    Location
    NYC, New York
    Posts
    18

    Default

    Kgober, thanks for the reply.

    I know it seems a little bit silly, but this machine means more to me than just a normal vintage PC. This was the machine my father brought home from his job in 1995 for my family when they were closing down. It's the first computer I've ever used and it's what got me interested in computers at such a young age. My father passed away in February suddenly and unexpectedly so it's been a very tough past few months for me. When I found the machine in my attic recently, after putting it away in 2013, I had a flood of memories come back from him and I using it when I was a kid. It brought me some happiness which I haven't had in a while. So I will do whatever it takes (including finding a new motherboard) to make it perfect.

    I want to upgrade the machine to be able to play Doom and maybe even take a crack at installing Windows 95 on it (not sure if I even can).

    I cleaned the sockets where the expansion boards go in, but sadly that didn't work.

    Do you think it could be a problem with the 4MB module that's currently installed on the mainboard? Is it possible that a parity error would show with the base module if more memory was installed in the system? I feel like it might because the memory check fails before it even completes checking the initial 4096KB of RAM. It halts at 4032KB every time, but only when an expansion board is installed. Just a thought.

  7. #7
    Join Date
    Mar 2017
    Location
    New Jersey, USA
    Posts
    463

    Default

    It's certainly possible that there's a problem with the system board memory module but it seems to me somewhat unlikely. Maybe adding an expansion card does something to the memory bus capacitance that causes a marginal system board module to fail? Trying a new module couldn't hurt, and they may be e a bit easier to find since the modules are compatible with multiple systems, unlike the expansion boards.

    I am not by any means suggesting that you get rid of this computer, I have a Deskpro 386/25e as well and it's the best 386 I've ever owned. I'm just not sure that it's worth running Windows 3.x on it. Mine has 16MB RAM but I still only use it for DOS games (X-Com, Civilization, F15 Strike Eagle, etc.), which run very well. I think that kind of thing is what this system is best at.

    Doom should run fine with just 4MB of RAM, but I wouldn't attempt Windows 95.
    Last edited by kgober; November 18th, 2018 at 04:14 PM.

  8. #8

    Default

    Quote Originally Posted by jetmike747 View Post
    I want to upgrade the machine to be able to play Doom and maybe even take a crack at installing Windows 95 on it (not sure if I even can).
    Win95 will install on such a machine, but that's about all it will do. As mentioned, you really need a 486 (and at least 8MB of RAM) for Win95 to really do anything of significance (without completely wearing your patience out). Doom would also run, but likely with the older Compaq video, it would be choppy at best.

  9. #9
    Join Date
    Apr 2011
    Location
    NYC, New York
    Posts
    18

    Default

    Kgober & T-R-A,

    Thanks for the input with 95. I'll just stick with Windows 3.1 for now just to have it. I'll mainly be in DOS because I wanted to run DOS games on it anyway.

    Kgober, do you have any plans to sell your 386/25e in the future? In case mine decides it doesn't want work haha. I have no idea how I'll be able to find another main board for it, and I want to upgrade it as much as possible. I want to get a nice sound card and maybe even a better graphics card to make it a truly bad ass DOS gaming PC.

    I'm going to try to find some modules for it, and see what happens with my fingers crossed

  10. #10
    Join Date
    Mar 2017
    Location
    New Jersey, USA
    Posts
    463

    Default

    Quote Originally Posted by jetmike747 View Post
    Kgober, do you have any plans to sell your 386/25e in the future?
    Not really; this is my only 386DX system so it fills an important niche in my CPU collection.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •