Compaq Portable III Restoration

 One of my contacts at Free Geek recently reached out, he had a computer that had been on my wish list for a while, a Compaq Portable III.  I already have a Compaq Portable I (which also was a project computer from Free Geek) and Compaq Portable II, and I really like these early Compaq machines because of the story of the company.  If you haven't read about it, I recommend Rod Canion's book "Open".

Anyway, this repair story starts with a water damaged Compaq Portable III.  It was quite dirty and since I'd been told it was water damaged I had quite low expectations, purchasing it as a parts machine for a future repair.  When I got it home, I immediately got started with cleaning since it was so dirty I didn't even want to touch it.  Here's a picture from "Before"...

Definitely too gross to work on.  After cleaning for a while I started to take the machine apart.  I was pleasantly surprised.  The machine was very dirty and dusty inside as well, but there were no signs of water inside.

The next step was a Power On test. I could hear some clicking from the Power Supply, but no fans, no backlight from the display or any other signs of life.  Then, there was a snapping sound and smoke!  I suspected a capacitor.  Testing with the machine off, there was a short on the 5 Volt power rail, which for this era of machines often indicates a bad Tantalum capacitor.  I was able to find the blow tantalum and replace it, and as soon as that was done the machine booted.  I was glad to see that the Plasma Display appears to be intact as this is the unique new feature that really sets this machine apart from the Compaq Portable II which still had a CRT, and the next generation from Compaq which had a more normal LCD display.

The system had the following errors, Keyboard Error, Disk Controller Error, and Time of Day / Clock Error.  The keyboard error and Disk Controller Errors were easy to resolve because these peripherals were simple disconnected.  I cleaned the 1.2MB 5 1/4" Floppy disk drive with a cleaning floppy and I was able to boot the machine from a DOS disk.

I also discovered that the Hard Disk in the unit had been disconnected.  When that was reconnected, I discovered that the disk was blank with only a few DOS files left on the machine.  I tried re-installing a newer DOS, but I was not able too do so, there are write errors when formating the drive, so I'm disconnecting it and replacing it with an SD to IDE adapter solution that I've used in some other vintage machines.  Based on this other helpful bLog article, I set the system up for a Type 42 hard drive which provides just over 500 MB of disk space for this machine on a 1 GB SD card.

Fixing the clock error proved to be the most difficult part of this repair.  This is important for these early Compaq machines because they do not have the BIOS setup program in ROM, you have to boot up from the Compaq diagnostics floppy every time the computer looses power and that make the machine alot less usable.  Apparently there were two different clock circuit options for the 286 version of this machine.  One option is the Dallas Clock chip, which are still being made today, but that is not the option this machine had.  This machine has a rechargeable battery which had been removed from this computer probably due to concerns about leakage.  I tried jury rigging a battery holder for a CR2032 battery into this space where the rechargeable battery was but I made an error in connecting that and my modifications were a failure.  After doing some more research online I found this fantastic article on MinusZeroDegrees.net.  This article contains enough detail that I thought I would try to switch my board over from the unobtanium battery pack too the Dallas clock chip circuit configuration.  I was able to make those modifications, and now I have a working battery backed up clock and drive settings!

I installed MS-DOS 6.22 on this machine, and copied many of my commonly used utilities over to the machine.  That wraps up the repairs on the Compaq Portable III for now.  It needs a bit more cleaning, and perhaps some day I'll find a RAM expansion for it, but for now I'm quite happy to have one of these in the collection.

Please reach out in the comments or via email (My email address is on my profile) if you have any thoughts about the Compaq Portables.