SWTPC digital microlab

[PE SWTPC microlab]

I purchased this PE MicroLab in March 2023, and did some restoration work as described here. This page was last updated Apr 9 2023 (C) Herb Johnson all rights reserved. Search my Web site to find other Web page content of interest. My home Web page for restoration of vintage computing is at this link.

Purchase and inspection

This PE magazine Microlab was purchased online at auction. The price was modest likely because of its rusty appearance. But the interior was merely dusty and looked in reasonable shape.

On arrival I examined the rusty front plate. Inspection showed it was a thin steel plate with some brass/bronze coating. It was dusty and had numerous rust spots on the underlying steel. Under the plate of course, was a printed circuit board.

Meanwhile I inpected the case and interior. This photo of the inner corner shows many features. The case is some kind of cheap grained wood, not pressboard. Note the IC is an MC789P with datecode "7011", that is 1970 and week 11 (March). Another chip has a datecode 1970 and week 35. Those are close to the March 1970 publication date of the Popular Electronics article which introduced the product, as available from SouthWest Technical Products. This model I have, has the PE logo. Many SWTPC products of course have the STWPC logo.


The interior looked sound and in reasonable shape. Note there's no AC power switch, or AC fuse! If you look carefully at the lamps, from front and back, they were likely inserted into the front-panel before installation and then wires soldered. The PE article describes that the posts are installed on the PC board before the front panel is inserted around them. I'll consider the assembly and disassembly later.


I used a few cleaners, from Simple Green to Bar Keeper's Friend. The latter is an alkaline slightly abrasive material used with water to turn rust into crumbly iron for removal. These were not effective on the iron oxide but cleaned the brass. Inspection of the black legends on the board, suggest these were likely silkscreened black paint or ink. Most of them were intact, some probably lost to wear.

Cleaning improved the surface but there was still some residue. Some areas were hard to scrub and the brass would shine up if buffed. This photo on a cloudy day shows the overall condition. This photo in clear sunlight shows the variations in among the pegs. I don't know of a clear remedy for the exposed rusted steel.

Support and parts

Here's a PDF of the PE article which includes assembly and schematic and how-to-use examples.. I haven't looked on the Web, for a SWTPC manual for the product.

Another issue is to acquire additional wires with the proper connectors. This unit came with one wire. Here's a photo of one of the terminals and the wire connector. The PE article describes these cables as something the builder produces. The end connectors are called "5/32" dia plated hair pin cotters" on "#24 wire" to connect to the "terminal posts". The fraction refers (I think) to the diameter of the circle formed by the circular arcs at the center of the pin. The posts themselves are some kind of steel, which I'll need to brass- brush to clean up.

Search of parts vintage and modern, shows hair pin cotters like are still in production. One brand says they are "made from [either] hard drawn MB spring wire zinc plated and baked, or Stainless Steel. It will take time and attention, to select plausible parts and build wires by soldering these cotters onto wires with heatshrink to cover the join.

Test and repairs

Of course, I'll have to test and restore the power supply and confirm the condition of the logic and lamps.

- Herb Johnson

Herb Johnson
New Jersey, USA
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Copyright © 2023 Herb Johnson