I recently picked up a blast from the past; a high-end vintage 1995 Compaq 486 DX4 laptop. This machine is a real piece of computing history, sporting a 486 DX4 processor and a modest 8MB of RAM (yes, that’s MEGABYTES, not GIGABYTES!). Back in its day, it retailed for nearly $2,500, which is roughly equivalent to about £1,500 today – a significant investment for a portable computer in the mid-’90s.
I bought it somewhat spontaneously, driven by curiosity and nostalgia, wondering if I could get it up and running again. Unfortunately, when I powered it on, I could hear the hard drive make a quick clunk and then nothing – it wouldn’t turn on. Rather than giving up, I decided to take it apart and see if I could identify the problem.
Upon inspection, I found that the issue was surprisingly simple to diagnose and fix. The culprit was a fuse located on the underside of the motherboard. This tiny component had failed, preventing any power from reaching the internal circuitry. Replacing the fuse was straightforward, and after doing so, the laptop powered on as if it were still brand new.
This experience led me to consider why the fuse failed in the first place. My theory is that the failure occurred during charging cycles. Over time, the internal resistance of the battery cells can increase as they age, especially if the battery has been used extensively or stored improperly. When the internal resistance rises, it can cause the battery to draw higher current or produce voltage spikes during charging, which can stress the fuse and cause it to blow.
Given this insight, I would advise anyone owning vintage or older laptops with batteries especially if they haven’t been used in a while to be cautious about using the battery in future. It might be safer to run the device directly from AC power instead of relying on the aging battery, which could pose risks of further electrical issues or damage.
Overall, restoring this vintage Compaq was a rewarding experience, not just for the technical challenge but also for reconnecting with a piece of computing history. It’s a reminder of how far technology has come and how sometimes, a simple fix can bring an old machine back to life.
I wasn’t entirely sure of the exact current rating of the fuses, but as a precaution, I decided to replace both of them with new 3A SMD (Surface Mount Device) fuses. Given their small size and high current capacity, these fuses are well-suited for vintage electronics and provide a good safety margin. After carefully installing the new fuses, I reassembled the laptop and powered it on; much to my relief, it sprang back into life.
However, once powered up, I noticed that the system wasn’t fully operational yet. The CMOS had a checksum error and the settings had been lost, which is common in older machines after being powered off for a long time. To get everything back to normal, I needed to replace the CMOS backup battery (a CR1220 button cell). This tiny battery keeps the BIOS settings stored when the device is unplugged, and over the years, these batteries tend to deplete or fail altogether.
Replacing the CR1220 was straightforward: I just removed the old one and popped in a fresh, new battery. Once installed, I powered the laptop on again, and it was ready to go – fully functional, the system running smoothly. It was a satisfying moment, seeing this vintage machine come back to life after so many years of dormancy and a few simple repairs.
For anyone who is interested in getting one of these with no HD up and running here is the AUTOEXEC.BAT and CONFIG.SYS files:
AUTOEXEC.BAT
@ECHO OFF
SET PATH=C:\CPQDOS;C:\;C:\DOS;C:\WINDOWS;C:\WINDOWS\CPQWIN;C:\LL5\
SET LMOUSE=C:\MOUSE
LH C:\MOUSE\MOUSE
SET PROMPT=$P$G
SET TEMP=C:\TEMP
REM C:\CPQDOS\HIBRN8.EXE
LH C:\DOS\NLSFUNC C:\DOS\COUNTRY.SYS
LH C:\CPQDOS\KEYB UK,437,C:\CPQDOS\KEYBOARD.SYS
C:\DOS\SMARTDRV.EXE 2048 512
rem UNDELETE /LOAD
rem C:\WINDOWS\WINCONFIG.SYS
switches=/F
SHELL=C:\DOS\COMMAND.COM /P /E:1536
STACKS=9,256
DEVICE=C:\DOS\HIMEM.SYS
DEVICE=C:\DOS\EMM386.EXE NOEMS I=B000-B7FF X=D000-D4FF
DEVICEHIGH=C:\WINDOWS\CPQWIN\CPQCM.SYS
DOS=HIGH,UMB
REM *** Begin PCMCIA Drivers
REM Warning: Do not move, reorder, or delete any of these lines.
REM
;DEVICE=C:\CPQDOS\PCMSMIX.EXE
DEVICEHIGH=C:\CPQDOS\SSVLSI.EXE
DEVICEHIGH=C:\CPQDOS\CS.EXE
DEVICE=C:\CPQDOS\CSALLOC.EXE
;DEVICEHIGH=C:\CPQDOS\ATADRV.EXE
;DEVICEHIGH=C:\CPQDOS\MTAA.EXE
;DEVICEHIGH=C:\CPQDOS\MTAB.EXE
;DEVICEHIGH=C:\CPQDOS\MTI1.EXE
;DEVICEHIGH=C:\CPQDOS\MTI2P.EXE
;DEVICEHIGH=C:\CPQDOS\MTSRAM.EXE
;DEVICEHIGH=C:\CPQDOS\MTDDRV.EXE
;DEVICEHIGH=C:\CPQDOS\DBLFLASH.EXE
;DEVICEHIGH=C:\CPQDOS\MS-FLASH.SYS
DEVICEHIGH=C:\CPQDOS\CARDID.EXE
REM *** End PCMCIA Drivers
BUFFERS=20
FILES=35
COUNTRY=44,437,C:\DOS\COUNTRY.SYS
Drivers (Mouse, PCMCIA etc.)
To download a copy of the drivers for this laptop please click the download button above.
Recovering the BIOS / Diagnostics Partition
These laptops do not have a physical onboard BIOS and as such rely on a BIOS partition on the hard disk.
The Compaq Contura originally shipped with two floppy disks:
Rescue Disk 1: Diagnostics
Rescue Disk 2: Setup