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.