Fixing a HP OmniBook 430

By Cèbe, . Permalink Retrocomputing

Every year or so, I try to run all the machines in my collection. As can be expected, the failure rate is going up every year, and there is not always an obvious "recap" fix. Sometimes, however...

The HP OmniBook 430 is a nice little machine featuring some nice additions such as MS-DOS on a ROM and a tiny integrated mouse. A particularity of the machine is that the BIOS / Firmware / DOS resides on a PCMCIA card and the laptop won't POST without it. It also has a Maxtor PCMCIA hard disk for conventional storage, and a RAM extension that provides a whooping 6 MB of RAM.

Until recently it worked just fine, but on my last testing session it suddenly shut down, never to start again.

Opening the pastic case was quite difficult. The old plastic became very rigid but luckily not brittle (yet) so a few clips had to break... The price to pay for this repair.

The caps did not look leaky and were not out of specs. I measured correct capacitance and ESR for each of them; or so I believed. Upon further inspection, the PCB did look a bit oxidated. Maybe those caps are not so respectable anymore!

After a good cleaning with IPA, it does turn out there was some oxidation developing underneath the caps!

I replaced the following caps:

  • 1500 uF 25V LXF noname
  • 1500 uF 10V PL(M) Nichicon
  • 2300 uF 6.3V PL(M) Nichicon

I removed but didn't replace the 3 "supercaps" GC 5.5V 0.22F -- I could only measure the voltage and it was clear they were not retaining any. They are most likely used for RAM persistence when the laptop hibernates. This is another great feature for 1993! But I don't need really need it today. One of the supercaps had a resistor directly attached to the + side (not soldered to the PCB).

Putting back the laptop together lead to another problem: the already flaky keyboard connector got even worse in the process, but a bit of double sided tape fixed it... for now.

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