Processor Tech SOL - Preliminary

Most recent revision of this page Aug 8 2012.

Introduction

I have a couple of Processor Technology SOL computers. On June 30 and July 1 2012, the MARCH club sponsored a vintage computer repair event, at their site at the Infoage museum and science center in Wall NJ. Myself and two other people (bill Degnan, Sudbrink) brought SOL computers. Bill brought a SOl and an IMSAI configured like a SOL; both could boot up the same CP/M. Follow the Web link for details. I brought two of my SOL's for test and repair. I only got to one of them, but I got it running. I'll describe that one here.

The event coincided with a visit by Lee Felsenstein, a designer and document author of the Processor Technology SOL in 1977, and designer of the Osborne 1 computer a few years later. On the left is a photo of myself (left) and Lee (right). Follow the Web link above for details on that talk.

Processor Technology SOL computers

IN this photo are two SOL's side by side. Bill Degnan's on the right in front; Herb Johnson's in the back on the left. These capacative keyboards can be operated "naked" by touching the keypads, as Bill Degnan demonstrates in this photo.I discuss my keyboard repairs below.

Bill tries an 8080 in circuit emulator on his SOL. It was not able to operate the SOL. All it would display when the ICE halted the processor, was this single line of random characters.

Fortunately for me, my (herb's) SOL came up to a prompt right after full power-up. It had been decades since this computer was last operated. The "prompt" is a little skewed because the monitor is not adjusted to match the SOL's video scan rate.

In this photo, my SOL is operated by Bill Degnan (left) and shows a hex dump on-screen. Lee Felsenstein (right) examines the CPU schematic, to determine the operation of the master clock and divider. The 'scope shows an output of the divide-by-seven counter which drives the CPU with a 2MHz clock. Lee worked out and confirmed the signal from reading the schematic - on the spot.

In this photo, Herb (left) gets an autograph for his SOL, from the co-designer Lee Felsenstein (right). In the background is Will Donzelli.

At the time above, I had forgotten Lee and I had some prior correspondence. Check this bit of discussion in 2002 about the Helios OS, and a 2005 update by Lee Felsenstein.

floppy controller

I was prepared at the MARCH event above, to add a working Northstar floppy controller. I brought a known-working original Northstar controller and single-sided drive, made for the SOL. That's why I brought the NorthStar Horizon system, if I had to construct a boot disk. But Bill's Sudbrink's SOL disks and drives were double-sided sided; and he did not arrive with his SOL and IMSAI until Sunday. So there was only time to ask him for copies of his SOL/N* disks. Thanks!

SOL keyboard repairs

Here's a series of photos about my (HErb's) work on restoring a SOL keyboard. Removing the keycap assembly, you can see the PC board. The keyswitches include a foam insert with Mylar/metalized pad (shown as brown). Here's the keycaps in closeup. The foam insert has disintegrated, leaving behind the plastic disks in the key assembly - one is shown removed. At the right, one of the keys pads has been replaced with a new foam-rubber and Mylar-capped insert.

This photo shows a bag full of those inserts, which I made beforehand. It's a tedious process to scrape out the key assembly the old foam, add a dab of cement, and insert the new foam insert. This picture shows that effort in process, keycaps in various stages. In a later photo, I've removed all the degraded old foam and started to add new foam/Mylar inserts. I was not able to complete this process during the June/July event.

My keyboard repairs got complicated. There are issues with how the key inserts are made, their materials, and what variations make a difference in use. I've had to try other materials and methods. Here's a link to a Web page with details about restoring a Sol keyboard.

Copyright © 2012 Herb Johnson