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


13 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!


  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


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