Sol 20 Terminal Computer

Sol 20 front
Sol 20 rear
Sol 20 keyboard
Sol 20 card cage top
Sol 20 main board
Sol 20 card cage rear
Sol 20 fan
Sol 20 ports
Sol 20 and ZVM-123
Electric Pencil logo
Electric Pencil
Microsoft BASIC
BASIC listing
BASIC5 listing
LIFE instructions
LIFE pattern
Dual drives
CP/M 2.2
Sol 20 Terminal Computer from 1976

CPU: 8080 @ 2MHz
Floppy Drives: Dual Shugart SA800-2 8" drives (single-sided)
Display: Zenith ZVM-123
Ports: 2 cassette ports, composite video, parallel data interface, serial communications interface
Model: Sol 20
ROM: SOLOS-1 Personality Module
Original Price: $995 kit

Before powering up the system, I took the precaution of reforming the two large capacitors in the power supply. The voltages checked out, although a little on the high side. On powerup, the monitor displayed the SOLOS > prompt. As expected, the keyboard was completely non-functional, due to the disintegration of the foam/mylar pads. I replaced the pads with the pads from a Sun Type 4 keyboard, and all the keys worked.

This system has 3 16KRA dynamic RAM boards installed, for a total of 48KB. The 16KB block from 4000-7FFF was not recognized; that turned out to be a dirty DIP switch on the board. Also, the 4KB page from 8000-8FFF would not take/retain data. I tracked that down to a faulty 74LS157 multiplexer chip on the 8000-BFFF RAM board. The system appears to be fully working. I loaded several programs (ENT files) through the serial port, and was able to run BASIC5, LIFE, Microsoft BASIC, and Electric Pencil.

The Sol 20 was designed by Lee Felsenstein, who later designed the Osborne 1.

Update (03/28/2022): I installed a Micromation Doubler FDC and connected a pair of Shugart SA800-2 single-sided drives in a nice wooden enclosure. I now have a 48K CP/M 2.2 system running on the Sol.

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Last updated on Monday, March 28, 2022