This is the 3rd post in a 6 post series on the Compaq Portable 386 Computer. In this section, we look at turning the computer on, getting it to POST, and taking a peek at the insides & motherboard. You can jump to:

  1. First Impressions
  2. The Gas Plasma Screen
  3. Booting Up & Opening Up
  4. The Floppy Drive
  5. The Hard Disk
  6. Installing MS-DOS
  7. Youtube VIDEO REVIEW

Now, I, like most people I know, don’t have much patience – I wanted the computer to work out of the box, but there were a host of issues that were quite difficult to troubleshoot and get working before I could even try to get the computer to boot successfully.

Press coverage from BYTE Magazine of the launch of the Compaq Portable 386, published November 1987.

Sockets, Plugs & Peripherals

Before we get into that, perhaps it’s best to take a quick tour around the machine to explain all the ports, plugs, drives, slots, and buttons.  

Looking at the machine’s front, you have the screen (covered in this previous post). On the unit’s left side, you have the standard 5.25” Floppy drive (which can be easily replaced with a much more useful 3.5” floppy drive) and a bay for the hard disk. The exhaust takes up the right side to vent the hot air coming from the power supply unit. On the top, you have a comically large, padded handle, running from end to end. Like the screen, it’s is also retractable (the handle makes it so portable and convenient!). I feel like they must have held a focus group on handle-comfort of the Compaq Portable 2 and deduced that they were really lacking in this department, but, the handle on the Portable 386 is a bit overkill.

The rear of the unit houses the serial port, the parallel port, an RGB connector (to an RGB display – not VGA), and also hidden behind a sliding door, a proprietary expansion port for the optional expansion box allowing two full-length 16-bit ISA cards – essential if you want to plug in a VGA card for an external monitor, sound card or memory card.

The expansion box adds bulk, but is necessary to add a graphics card if you want to use an external VGA monitor.

Note that this computer does not have a battery for power – all references to the “battery” on these units refer to a tiny lithium battery used to keep the CMOS memory from forgetting it’s BIOS settings. In fact, most “portable” computers at the time were not designed to be used “in transit” (like a modern laptop) – they were designed to be moved from place to place and plugged into AC power at your destination. They were marketed to people who traveled or who wanted to take their work home with them. (maybe we have Compaq to blame for all those weekends lost to working from home!)

Michael S. Swavley, vice president of marketing for Compaq Computer Corporation, introduces the Compaq Portable III at the Mark Hellinger Theater in New York, Feb. 18, 1987.
“The Compaq Portable III, starting with a weight of 18 pounds, provides the power and function of a high performance desktop computer in a small, self-contained unit that is easy to carry.” (AP Photo/Richard Drew)

The Compaq Portable III and 386 take a standard “computer plug” (if you really want to know, it’s called a C-14 type) and auto switches between 110 V and 220 V. Plugging it in and flicking the power switch at the back produces a satisfying click and the machine whirrs to life.

POST (Power On Self Test)

On booting, the computer does some instant basic diagnostics – such as checking the system board for faults and checking the CPU – if all is well, the screen should instantly flicker on in a nice warm orange glow – followed by a RAM counter to check each KB of installed RAM.

I’m messing around with an ISA RAM expansion card in this image, so the memory count is at an odd number. Typical configurations are 2 MB, 4 MB, 8MB and finally, 10 MB – which in 1987 is massive! Almost as big as a typical hard drive at the time.

The memory check does some basic checking to see how much (continuous) RAM is available – including those installed on the motherboard, the proprietary expansion cards, or those installed on a properly configured ISA ram card via the expansion box.

After the ram check, the machine will try to boot using the CMOS settings provided, meaning it will try to boot from the floppy drive using the drive settings specified. If it can’t find anything a readable disk in the floppy drive, the computer will move on and try to boot from the hard / fixed disk. If you don’t have either set up properly, you will see the message below:

This message is asking you to insert a system or “diagnostic” floppy disk as the computer can’t read the hard disk and needs to boot from its floppy drive. If you see this error even with the correct diagnostics diskette inserted, don’t worry, there is hope! Take a deep breath and grab your power screwdriver – you’ll need to open the computer up to clean or replace the floppy drive and also likely replace the hard drive.

I don’t know about you, but I enjoy opening up computers and exploring what’s under the hood. This older computer is particularly interesting as there are many jumper settings and removable parts that can be fiddled with… without too much frustration.

Disassembling The Compaq Portable 386

The complete disassembly instructions can be found here. You’ll need a set of Torx (star-shaped) screwdriver heads and ideally a power screwdriver. Start by lying the machine screen side down on a flat surface and remove the 6 screws on the back. The screws in the corners are long screws that hold the whole machine together; the two in the middle at the top and bottom hold the rear panel to the rest of the case.

Give the rear panel a gentle jiggle, and the rear of the computer case should come out. Pull up then away to reveal the motherboard underneath. For full instructions on the rear panel removal, see here.

The system board of the Compaq Portable 386 – The ribbon cabled on the left are for the hard disk and floppy drive, on board ram is in the middle, and CPU is inside the protective metal box, top right.

The photo above shows the motherboard after the protective shielding has been removed – you can see the CPU and Math Co-processor on the top right. Below that on the right edge is the socket for the battery to keep the CMOS settings. On the bottom right, you have the serial, parallel, and RGB video output ports. Continuing along the bottom edge, in the center, you will find the ribbon cable connection for the graphics card underneath, and past that is the connection (and space) for the hard-to-find 32-bit memory modem expansion interface for the modem card/memory expansion boards (which can provide up to 10 MB of RAM).

Here’s the 386 CPU that sets this machine apart – most amazing thing is that it is socketed, meaning all sorts of fun CPU upgrades are possible.

It’s more than likely that one or more of the items below will need to be repaired or replaced; luckily, assembly and disassembly of this computer is relatively easy.

  • Hard Disk – these are one of the first IDE drives developed ranging from 20 – 300 MB. Due to age, they likely won’t spin up. If they do, download and archive what’s on the disk while you can. You can replace this with a Hard Disk or, better yet, a CF Card
  • Floppy Drive – 32 years is a long time to accumulate dust. Take a look under your fridge for reference. These wide-mouthed 5.25″ floppy drives usually are very dusty and thus fiddly to get working consistently. Be ready to change drive belts and apply lubricant to get them fully working, or, more than likely, you will have to replace it. Alternatively, you can easily upgrade the floppy drive to a 3.5″ – covered in this post – making it much easier to transfer files from your main machine.
The “fixed disk” and 5.25 Floppy Drive reside in this easily removable caddy on the Compaq Portable 386
You can replace the original floppy drive with this relatively more modern 3.5 inch floppy disk drive. The BIOS supports 3.5 inch drives without a problem.
  • CMOS Battery – You will need this to keep the CMOS system settings in the memory alive. Believe it or not, some people have these units where the lithium battery is still ticking and giving current for the CMOS to save settings. You don’t really want to count on that, though, and it should be replaced – a CR2020 3v button battery makes a good choice. I simply snipped off the old battery’s connections and sandwiched a CR2020 between the leads, checked it with a multimeter, and then secured it with electrical tape. 
  • Visually inspect the Motherboard – check for jumper configurations, any blown tantalum capacitors, and see if you happen to have any optional (and extremely expensive) memory expansion boards. These are so rare that one seller on eBay has listed a unit with one of these installed at US$999.99 – here’s my 10MB upgrade card below – it’s aftermarket, made by Kingston Technologies.
10 MB of RAM for a 1987 Compaq Portable 386 – This option cost almost $10,000 when released in 1987!

So hopefully, you now have an idea of what you need to replace. If you have to replace both the floppy disk and the hard disk, or if you are not sure if your hard disk is working or not, and your floppy drive is not working, definitely, replace the floppy drive first.

If your floppy drive is working but you can’t get boot to your hard disk, see what your choices are for replacing the hard disk

Don’t forget to check out my video review below:

Booting Up, Then Opening Up

Post navigation

5 thoughts on “Booting Up, Then Opening Up

    1. hi eric,
      did you ever get a diagnostic 5.25 disk? i am in dire need of one myself. if you have one would you make a copy? my 386-25 is used for cadd only and was working great,untell the fan failed.the disk drive board had to be femoved to replace the fan,on restart it asked for the diagnostic disk which i cant find.
      regards bob

      1. Hey Bob, I have swapped out my 5.25 drive for a 3.5 floppy disk drive so I only have those. Do you have access to a computer that can boot? You can download the images online and write them to a disk.

        1. Hi am I glad to hear from you…I am not very computer savy. The computer I am using to chat with you is running on XP which has a 3.25 disc My Compaq is not online….so could you send it to my email then could I copy to a 3.25 disc and use in the compaq?. If you would like to call my number is 925 838 0582

Leave a Reply

Your email address will not be published. Required fields are marked *