Released 1987: The Compaq Portable III is a PC/AT-clone computer released by Compaq Computer Corporation in 1987. It was advertised as being much smaller and lighter than the previous portable x86-PCs, however it was still quite large by today’s standards. Its street price upon its release was 4999 USD for a model equipped with a 12 MHz Intel 80286, 640 KB RAM, 1.2 MB 5.25″ floppy, 20 /40 /60 MB hard disk, and a 10″ amber colored gas-plasma display or 5799 USD with the upgraded 40 MB hard disk. There was also an optional ISA Expansion chassis allowed for two full length 16-bit ISA add-in cards. Power is supplied using a mains electricity outlet, no battery exists.¨


  • Manufacturer: Compaq Computer Corporation
  • Type: Portable computer (dragable)
  • Released: 1987
  • OS: Compaq DOS 3.1
  • CPU: Intel 80286 @ 12 MHz (FPU possible)
  • Memory: 640 KB (upgradable with expansion board)
  • Display: 10″ gas-plasma display
  • Graphics: Up to 640 × 400 pixels monochrome
  • Storage: 20, 40 or 60 MB hard drive, 1.2 MB 5.25″ floppy drive
  • Sound: PIT (PC speaker)
  • Connectivity: CGA, serial, parallel
  • Dimensions: 41 x 19.2 x 24.8 cm
  • Weight: 9.1 kg
  • Predecessor: Compaq Portable II
  • Successor: Compaq Portable 386, Compaq SLT/286

Repair and upgrades
Got this one from a college at my job. An error message about inserting the “Diagnostic disk” and “no settings found” on startup. The machine and keyboard also needed a throughout clean, and the keyboard coil cable was “rotten”.

A friend has an vintage PC with 5.25″ floppy drive and he made wrote me a Compaq DOS 3.1 floppy, I’ve also found the diagnostic/BIOS setup software for this model on Internet and copied it to an floppy. This model got no BIOS setuo software built into its ROM and needs to run the setup from disk.

Turns out, this computer got a non-rechargeable battery integrated into an special IC chip “Dallas chip” for storing the CMOS/BIOS settings. No surprise, the battery was long gone. The “Dallas chip” contains a small amount of CMOS RAM and the RTC (clock) as well.

Dallas “RTC” chip: I removed the chip from the main board, luckily it was already in a socket. I used a carpet knife to carefully scrape holes exactly where the ground and plus for the battery are located (above pin 16 and 20 I think). I cut the ground leading to the integrated battery and soldered on two wires for a new battery. I removed a battery holder from a cheap Christmas decoration snowman I had laying around. Finally, I inserted the fixed chip back on the main board again. The computer now remembers both CMOS settings and time, this is necessary for an hard drive to work as to correct type of hard drive needs to be preset from a list.

The “Dallas”-chip for CMOS settings was given a second life with a new battery.

Harddrive: The original 2.5″ Conner harddrive was “dead”, no surprise really. I removed the drive and tested it on an Linux PC with testing software to make sure it was really dead. The computer uses an IDE/PATA harddrive, so a CF memory card adapter should work as a replacement. I installed a CF card and a CF-IDE adapter, it worked perfectly for a few minutes, then it froze. It was not going to work with this adapter or CF card.

Then I got an SD memory card adapter for the IDE/PATA controller instead, I was told this was more compatible with old IDE interfaces. I got an 128 MB SD card laying around. I managed to setup and format an 102 MB partition. To make it autoboot, I had to use the unofficial option “MBR” for the FDISK command, FDISK /MBR. It forces the boot sector i be written on the card, or something like that. Luckily this worked.

The original Conner IDE/PATA 2.5″ hard drive, 63 MB.

Keyboard cable: Keyboard cable cover plastic was in a terrible condition and was cracking and falling off. I found a coiled keyboard extension cable with the old 5 pin DIN connector on eBay. It was very difficult the split the keyboard open without breaking any of the clips, three of them broke even when I used my time on “wrestling” it. Then I had to just measure with my multi-meter what color of wires corresponded to the old cable and solder it onto the keyboard PCB very carefully. It turned out great.

Replaced the old cracking keyboard cable with a new.

Floppy drive: The plastic eject button was missing. I made a 3-D model of the eject-button by looking at photos and measuring. I also first made a wood mock-up to be sure I got it right. It fitted just perfect. When I was at it I also lubricated the moving parts inside to floppy drive.

Made a new eject button, the original button was missing.

Mouse and FPU: As a bonus, I was lucky to find an old serial port mouse for it laying around at my job. I also installed an 80287 @ 8 MHz FPU, just because it was a free socket for it.

Update 2022 – floppy drive : Got parts from another machine and replaced the floppy drive with my 3D-printed eject button. Now it got a drive with an original eject button.

Update 2022 – keyboard: Took the key caps apart and had them submerged in hydroperoxide ‘hair bleach cream’ for a few days. It reversed the yellowing.

My Compaq Portable III running Windows 2.1 and Excel.
My Compaq Portable III running Windows 2.1 and Excel.
Compaq Portable III

Remi Jakobsen

I'm collecting classic computers and video games, stretching from the 70's into the 90's. Restoration, history, usage ...

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47 thoughts on “Compaq Portable III

  1. Thanks for the info. I am waiting for my Compaq Portable to show up and see what needs to be done to make it fully operational!

  2. Nice Job on this lugable, how did you get the setup floppy made?
    I’ve been trying for a while on mine and the exe made floppy wont boot
    you wouldn’t have the files in the disk I can toss on a dos 1.44 floppy?

    1. Thanks. You can boot with any 5.25″ HD 1.2 MB or DD 500 KB MSDOS (or MS Compaq DOS) boot disk. As you probably already know, you make an MSDOS boot disk by using the “SYS” command or by runing the SYS command by adding it to the FORMAT command parameter, like this: “format A: /S”. I can send you the Compaq setup program or disk image files for Compaq DOS.

    1. If I remember correctly, on mine, it was clipped together, must be very careful, take your time and not break them. But I think there is another variation with “hidden” screws instead of clips, maybe hidden between some of the key caps, so you have to maybe remove a couple of key caps to get to those.

  3. Ok thanks good to know. Not sure if you’ve come across this issue, but the screen on mine has several black lines going vertically. Is this something that can be repaired, or can this be written of as a failed screen.

  4. I don’t know. It’s a gas plasma screen. I repaired a Macintosh Portable with LCD screen with stripes. The missing stripes was caused by broken wires in the monitor flat cable going to the main board, maybe you should measure the connectivity in the cables to the display panel. (BTW: as you probably know you can connect an external cga/rgb monitor and use a hot-key to switch to that screen).

      1. Whatever is fair – not looking to make anything on it… just want it to go to a good home. 🙂 I’m going through gear and cleaning house. Let me see what else I have and I’ll shoot you some pics. thx

  5. This is fantastic! I just picked up one of these and want to get it restored. Right now I’m getting a 201 memory error.
    Mine does not have the Dallas “RTC” chip I have the M146818P chip. Would I still need to change that out for a battery? Thanks!!

    1. I don’t know that chip, if the battery sits in that chip you need to replace it somehow I think. However you should be able to boot from a floppy even with dead battery and the default CMOS settings. If you got a memory error message, maybe there is a failed RAM chip on the motherboard that needs to be replaced, I would have started with that.

  6. Please, can you tell the output voltages values for te power supply’s connectors? The 12 pin and the molex. Please, i can’t found the information anymhere!!

  7. Very good job Remi ! I recently found the same computer, a Compaq Portable III but fitted with the Compaq 3″ 1/2 drive instead of 5″ 1/4. This computer is in very nice shape and still power on.
    Unfortunately I have no floppy disk and I will need this indispensable COMPAQ DIAGNOSTIC DISK to setup it.
    Would it be possible to get an image disk (diag & Compaq Dos) to build one, in 720ko 3″1/2 format if possible ?

  8. Hello Remi,
    Sorry, I hadn’t seen your post earlier but since my last one I’ve made some progress. I found the SP0308 file on and with a new 3 “1/2 floppy formatted 720Kb (/ T: 80 / N: 9) I managed to run the program to create the diagnostic floppy (with the QRST.EXE program), this done with an old laptop running Dos.
    Unfortunately (and after several tries), everything goes correctly until the last track but stops with an error message “A checksum error as occured. The diskette just build is invalid (does not compare with the MASTER)”
    Wouldn’t this come from the Dos version used ? Should this operation be done under a specific Dos (Compaq Dos) ?
    Thank you for your help.

    1. I don’t think the DOS version matter, it can boot any version. I’ve got SP0316.exe that you can start in DOS and use to make two 360KB 5.25″ setup disks for it. I can send it to your e-email if your interested, just tell my where to send it.

  9. Thanks Remi but my Compaq is fitted with a 3″1/2 drive, so a 5″ floppy disk would not be of any use to me.
    I will redo other tests soon. I just refurbished an old Compaq Presario 1260 by replacing its bad floppy drive, and it now works perfectly. I will try to find some other Dos floppy disks in my old stash, and I hope it will work now.
    Thanks again … and Happy New Year !

  10. Hi Remi;

    Nice job on the Portable III! When this PC came out, it was the best PCompatible you could buy with a handle on it. We had some at work, and I always enjoying using it. The amber plasma display is beautiful!

    Anyway, I have restored a Portable III and an Oki Microline 320 Turbo printer. The printer works fine, but is noisy and slow. I would like to upgrade to a laser printer.

    Do you have any experience using Lexmark laser printers with DOS PCs? They still make laser printers with parallel ports on them!

    Thank you, and great job on your website.

    1. Hi Greg, thanks for your comments. Yes, the gas-plasma display is great compared to the LCD’s at the time. I’ve almost no experience using printers with DOS PCs I’m afraid.

  11. Hi I’m looking for a 5.25 setup disk and diagnostics disk. It’s very hard to come by and there are no writeable 5.25 to usb drives. A pc with a 5.25 and a 3.5 inch both is also a rare find to come across. Would you be able to send a Setup disk? I have a 3.5 parallel drive to attach once I get things started for easy software use though it is unable to do anything without having the computer ready to go. Thanks!

    1. If I remember correctly, you need only the small setup program to config the CMOS/BIOS. If you have a 5.25″ MS-DOS bootable floppy somewhere, you can boot from floppy and transfer the setup program from another PC using a serial (COM-port) null-modem cable. Another method could be to install a GOTEK (floppy emulator using USB stick), and put the disk image file of the “setup disk” onto a USB stick and boot from the GOTEK. If not, I will send you a floppy, but I will need your address and stuff. I see someone on eBay is selling copies of the setup disks, and they also “stole” my photo for adverting this: Maybe the easiest way for you is to simply buy one from there:

  12. Hi Remi,

    I have a pristine Compaq SLT 386s/20 complete with original Compaq carrying case. Boots to DOS but without the setup disk that’s as far as it goes. Comes with a Microsoft Serial Mouse. If I can secure the startup file(s) I can create the startup disk. HP supposedly has the zip files but for the life of me I can’t remember how to access ftp.

    1. Seems like you got a great setup there. If it boots to DOS is obviously works. You could Google to find the setup disk, download it on a modern PC and transfer it to a machine that got a 5.25″ floppy drive to make a physical diskette. An easy way to transfer the zip file is using an USB 3.5″ floppy drive on your modern PC, you get them for next to nothing on eBay.

      1. Does it matter that it only has a 720 3.5″ drive? Haven’t opened it up to see what kind of HD it has but do hear one spin up. To the right of the 3.5 there is a vacant bay of some sort. Doesn’t appear wide enough to support a 5.25.

          1. Remi,

            Thank you for answering my questions in a timely manner. Though I haven’t created the setup disk yet I’m confident that will go smoothly. Last thing to do will be to try and breath some life back into the battery.
            Again, thank you for your help.


  13. I have found a Comaq III (Model 2660) in my office where it has sat, (untouched but air conditioned) for the last 30 years. I held on to it as it was from the company I used to work for and it reminded me of my boss who had passed away, so I held on to it. Now with the move home, I figure it is time to see if it worth something to someone. Also as an organ donor, I realize that maybe the parts can be used by someone for something. Is there hope?

  14. Hello Fred;
    I love the Portable IIIs and their amber screens. I have a lovely one that I restored sitting on my desk, and use it regularly. Always on the lookout for systems and parts. Do you have a description of yours? Floppy drive size? Disks? Carrying case? Printer? What would you want for it? Thanks, Greg.

  15. Hi: I just found a Compaq 2660 in my closet. Its over 30 years old. I also have the carrying case. I plugged it in and the power is on but nothing comes on the screen. Anything I can do to fix it? Alos, any idea where I can sell it? Send a response to my email. Thanks

    1. Hi, could be many things, maybe just a loose connector, power supply output voltage to mainboard wrong or anything.

      You can sell locally or on eBay if you don’t mind the hazzle. A fully working machine usually change hands for around 100 usd, so don’t expect to much for a non-working unit.

  16. Hi I’m waiting on one of these arriving and I’m curious about the keyboard connector at the machine side. Does it use a standard AT connector you mentioned a keyboard extension and it having a 5pin din. But then only talked about the soldering at the keyboard side. Did you happen to record which pins go to which connector on the keyboard? Obviously I can use a multi-meter when it arrives

  17. Hello Remi,
    I am also trying to use a SD to IDE as HDD, which settings did you use as HDD type and which settings in FDISK?
    Compliments for your work and website!
    Regards Rolf

      1. Problem solved! Formatted the SD card again, it was a used one and therefore not properly recognized by the computer!
        Just a question, did you manage to install a GOTEK floppy emulator on the PIII?

  18. Do you still own this? Would love to see it with Windows 3.0, the ISA expansion and ISA 16-bit graphics/audio card and an ISA 16-bit ethernet card!

    Not sure what the use cases would be. But it would be interesting, certainly.

    Take it to a retro LAN?

    1. I still own it. I’ve retro-brightended the key caps since last time, and got the ISA expansion. I’m not taking it tp retro-lan most likely, I’m more fond of Amiga computers and pre lan-gaming of the 90’s Taiwan PC’s.

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