Hugo Holden
Veteran Member
I saw that Sol-20 board for sale too. I noticed that somebody in the past had fitted a non standard D-25 connector. The original ones are still available on ebay if you hunt around, they had a relatively long reach from the position of their pins to the actual connector shell. A similar design was used on the serial connector on the Votrax type & talk and I had to find one for the replica. And it looks like two of the DIP switches have been replaced, probably a good thing. The original pale blue CTS dip switches in my Sol were intermittent and I replaced them with Omron low profile types in sockets. Watch out for the errors in the manual relating to the DIP switches and baud rate settings. The long job you have here is cleaning all the individual IC pins, and testing every socket claw with a dummy IC pin. I found quite a few damaged socket claws in my machine, and if not fixed it creates a minefield of intermittent faults, much like the DIP switches. You are fortunate though, most of the sockets do not appear to be the TI type, but the more reliable dual wipe type resembling a modern socket design. Though it is possible they are single wipe. The character ROM might be in a TI socket.
Your board seems to have had a good number of mods on the bottom, by the look of the wiring.
I collected a number of those white ceramic NEC 8080's as I thought they looked quite pretty, but somebody mentioned they had an odd quirk compared with the Intel IC, but I cannot recall what that was. Or maybe it was the NEC 8088 that had the quirk.
I also noted that somebody had installed non-standard relays for the tape motor control on your board. Probably they got annoyed with the original DIL relays contacts sticking together leaving the motor stuck on. This happens because in most tape units there is a filter capacitor in parallel with the motor and the surge currents charging that cause the problem. PT ameliorated this later by placing resistors in series with the contacts, as a mod, to limit the current, but not ideal as that limits the motor starting torque. In my machine I used new DIL relays in sockets, but I modified my tape decks with a driver transistor (edit typo) added to the motor circuit to reduce the relay contact current that way. (see end of article)
I wrote a detailed article on the Sol's cassette interface because I found the design of it very interesting and it is an analog meets digital circuit. It has a very simple and effective amplitude levelling circuit at its input using a jFet:
Your board seems to have had a good number of mods on the bottom, by the look of the wiring.
I collected a number of those white ceramic NEC 8080's as I thought they looked quite pretty, but somebody mentioned they had an odd quirk compared with the Intel IC, but I cannot recall what that was. Or maybe it was the NEC 8088 that had the quirk.
I also noted that somebody had installed non-standard relays for the tape motor control on your board. Probably they got annoyed with the original DIL relays contacts sticking together leaving the motor stuck on. This happens because in most tape units there is a filter capacitor in parallel with the motor and the surge currents charging that cause the problem. PT ameliorated this later by placing resistors in series with the contacts, as a mod, to limit the current, but not ideal as that limits the motor starting torque. In my machine I used new DIL relays in sockets, but I modified my tape decks with a driver transistor (edit typo) added to the motor circuit to reduce the relay contact current that way. (see end of article)
I wrote a detailed article on the Sol's cassette interface because I found the design of it very interesting and it is an analog meets digital circuit. It has a very simple and effective amplitude levelling circuit at its input using a jFet:
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