Compaq Portable III


Wiki – setup disks

Product Bulletin
Motherboard jumpers
Service Manual



The computer will not access HDD when the CMOS battery is discharged or absent. There are two versions of the batteries possible:

  • Integrated inside Dallas DS1287 real time clock controller chip. It is easy to replace the integrated battery with an external one, following these instructions. Please mind that my computer is missing the back cover, so maybe the battery needs to be positioned differently, but the idea is basically the same.
  • Separately soldered to the board, with MC146818 chip instead of DS1287 – this version will have additional resistors, diodes and oscillator soldered near the chip and the battery. These components are missing in the Dallas version where some zero-ohm links are soldered instead.

Video Board

Floppy Disk Drive

Canon MD 5501

Hard Disk Drive

Conner CP3041

Power Supply


Panasonic MD400F640PD5 – gas plasma display.


This is not the original keyboard coming with Portable III, but one taken from Compaq Portable 386. The keyboard seems to be compatible, also physically fits the cover perfectly.

Compaq Portable keyboards had cords in which the plastic cable coating broke easily with time and fell off leaving the bare cables visible. A vintage keyboard extender may be used as a replacement.



Signal at pin 2 of the LCD screen 4-pin power connector


27 thoughts on “Compaq Portable III

  1. Hi, you can tell me the pinout scheme voltage of the 4-pin red molex connector that powers the LCD screen. Then the voltage is in DC or AC? please.


      1. Thanks. The purpose is to replace the original power supply with a modified atx pc or a modular power supply.


    1. thanks for your help. That white connector then connects to the red molex connector of the main power supply. Are the 200 dc volts negative?


  2. Love the machine and this is some excellent documentation! I have a Portable III myself, and am in the middle of replacing the old frayed keyboard with a new cable. I made the mistake though of not documenting the pinout of the old cable, and every combination of wiring I can think to try from the new cable to the keyboard’s internal connector doesn’t seem to work when testing on the machine. Do you happen to know the pinout between the keyboard port on the machine to the keyboard’s internal connector? Thanks in advance!


      1. Thanks for the reply and sorry this one is late as well! I have not yet solved my keyboard wiring. If you ever get the chance to open up yours and see the wiring that would help greatly!


      2. Greetings, to late but i’ve seen your topic and i’ve just dismounted a portable III keyboard and made some measurement …

        i’ve photos of motherboard with color wires and i’ve measured which wire goes where…
        If you want i can give you if webmaster give you my mail adress
        best regards.


  3. Does anyone have the pinouts for the power supply connector to the motherboard? I have a dead computer, and trying to start by verifying if I have a bad power supply. Turning it on, the only thing I get is a click from the relay. Both with and without everything hooked up. Thanks


  4. Hey Pawel, thanks for this trove of info! I’m missing all the screws holding the mainboard onto the chassis, but they don’t appear to be standard M3, and the service manual just says P/N 107386-001 but not what they actually are. Any idea on what thread pitch and size they are? Cheers!


    1. Hi silvervest1

      Just looking at a Compaq Portable 3 that I had in the loft.
      Motherboard has been trashed by the leaking Lithium battery!
      The screws I have removed appear to be ANC No 6 thread. 0.138″ od 32 tpi



    2. Sorry…..I’ve given the case screw info!

      The Motherboard screws are smaller : ANC 4 – 40 0.112″ 40 tpi




      1. Hey Mick, that’s fantastic, thanks! I needed the case screws as well so that’s tops.
        Are you able to measure their lengths as well? I’m guessing just based on the mounts that 1/4″ will be fine but nice to know!


      2. Hi Silvervest1

        Motherboard screws are 1/4 inch thread length with a T-10 star socket head and have a captive shake-proof washer.

        The case screws are T-15 star socket head with a plain washer.
        The two short ones for middle of the back are 1/2 inch long thread.
        The four corner screws are 4 inch long shank with 3/4 inch of thread.




  5. Hi,

    I’ve recently acquired this type of old crap and for a while I was super happy. It didn’t last long as it did last for only 20 minutes and ever since I am the devastated. Seems like during a power cycle something died in the power supply because since then the plasma display won’t light up. ( The computer itself boots up, the logic power train is fortunately a totally separate circuit in the PSU ) I’ve disassembled it to almost atomic parts, took the capacitors out, checked every transistor I could find, and they seem to be fine.

    I’ve took some measurements on the high voltage outputs, and I was shocked to find this:
    pin 1: ground
    pin x: n.c. ( an intentionally missing pin as protection against general stupidity )
    pin 2: -120V
    pin 3: -200V
    pin 4: -195V

    As this makes no sense whatsoever in respect to the measurements Pawel took ( except reading it backwards ), I assume I am now in need of a schematic or someone that is kind enough to help me and has access to a working Portable III.

    Please help, or else… 🙂


      1. Hi Pawel,

        thanks for the fast response. I’ve also took my measurements on the display connector. The marking on the display PCB says:
        1 – GND
        2 – n.c.
        3 – +HV ( positive high voltage from ground, should be +200V –> on the PSU PCB the wire is marked 200T )
        4 – -LV ( negative logic voltage from ground, so this should be -5V )
        5 – -HV ( negative high voltage from ground, I guess -200V, but no clue —> marking on PSU side cable says 200N )


  6. Awesome information and pictures! I have just opened up mine, and there seem to be some revisions and differences here and there. You have a socket for a Dallas chip, where mine has a CDP6818E RZA Z 801 chip soldered on that spot. Where you board has the empty square next to the power delivery of the board, I have a big Lithium Battery, Compaq part number 107157-001. Which seems to be a bit harder to replace. It is soldered onto the mainboard with 4 pins. Will come back to your site a lot I guess for all the great information. Thank you for sharing this and keeping the site running.
    Regards, Jasper


    1. Hi Jasper

      The large Lithium battery is not soldered onto the motherboard that I have.

      It is a push fit into position by four projecting pins on the bottom of the package.

      They assembled it with a blob of adhesive on two side presumably to stop it from working loose
      while the machine was being transported.

      I’ve just made a holder for a Lithium cell type CR2354 that fits the same way.




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