Old Computer Restoration Notes


Over time, I have come to believe that computer restoration is in some ways similar to other antique restorations, and in others ways very different.

The conventional wisdom with antiques, in general, is to preserve. Stabilize. But don’t change it, lest you may lose the history. For example, with antique furniture, you never would want to strip old varnish or paint. Cars are different (and similar to computers), because as parts wear out, similar replacement parts may or may not be available, and so change (at least minor change) is almost guaranteed over time. Rustproofing and repainting an old car is accepted, and encouraged.

But computers are far more complex than even cars, and have more subtle and/or complex failure modes. You almost certainly can’t operate an antique computer without maintenance, and maintenance means change. (This reminds me of a Japanese story TODO-find-reference in which they tear down and rebuild a wooden temple every 50 years. The American is appalled at the loss of “history”, but the Japanese see it as a means of continuation of history. Perspective. What exactly do you value here?)

I find computers only interesting when they are operating. A computer is far more than the physical piece. It is the software and the knowledge and the way it was used. Museum pieces can just go rot. With computers, use it or lose it.

And so… how to keep them operating? This page is just a high-level overview, as I build out my own notes.

Removing Bad Capacitors

Electrolytic capacitors are common because they’re cheap. But they contain an acidic gel that can leak or dry out over time. Leaked electrolytic capacitors look about like spilled cola. But it’s acidic, so it can start corrosion that can eat into the PCB and break traces. You’ll want to remove all electrolytic capacitors, clean and repair the damage, and replace them with with tantalum.

Surface mount

If possible, clip the cap off the leads first. Easier to remove each lead separately, and less heat is needed. Sometimes twisting the cap gently helps; old solder joints sometimes just give. But be careful to not pull up the pad off the PCB.

Soldering tweezers are often recommended, but I’ve never needed them.

How to neutralize acid from leaked electrolytic capacitors? First pass, I scrub with Q-tips and rubbing alcohol, then as a second pass, scrub with hydrogen peroxide or baking soda. Rinse.

Cleaning

First, remove all socketed chips and bad capacitors.

Or water with mere drop(s) of non-polar (non-ionic) detergents, with multiple rinse cycles of plain water.

98 - 99% pure dehydrated ethanol alcohol may be useful as the final rinse, because it will pull water out (faster than leaving the board out to dry for several days).

Cork Pads

Old computers often had cork pads on the bottom of the keyboards and main units. Over time, these move around, become un-grippy, or peel off completely.

Lorne on Vintage Computer Marketplace sells authentic cork replacement pads for old IBMs. He’s great to work with.

TODO: How to make otherwise good cork pads grippy again? How to cut the old glue, clean, re-grippy-ificate, and reglue?

Metals

After washing dirt off unpainted metals, I apply a thin coat of gun oil (or similar), work it well into any pits in the metal, and wipe off any residue. Good oils are slow to evaporate and have corrosion inhibitors.

Plastic Restoration

Retr0brite

Carefully watch the plastic in the sun. As soon as the reaction has finished, bring the case back inside. Apparently, once the reaction has finished, the plastic is no longer protected and can very quickly reverse course and yellow again. Perhaps a thicker coat of Retr0brite might make work better.

Or keep it moist in the sun for 2 hours with a repeatedly sprayed solution of: - 14 teaspoon Oxi-Clean - 500mL 3% hydrogen peroxide - mix in spray bottle

Software Archiving

Reading floppies.

Diagnostics

Some systems shipped with diagnostic software. Find it. Run it.

Schematics

You can’t seriously troubleshoot a board without a schematic. Find it.

Updated January 1, 2014