Visited a small retro gaming event this weekend and came home with some cool new vintage computing junk. In particular I finally got hold of a Commodore Vic-20. This was my first computer back in the eighties so it holds a special place for me. It is in good condition, even has the first(?) ceramic revision of the VIC video chip. However it’s not the model that takes the C-64 type of power supply, instead it has a two prong connector which should feed the vic with 2 amps worth of 9 volt alternating current. I had some 9V ac wallwarts laying around so I decided to try it out if the thing is in working condition.
Turns out that the wallwart rated at 1A isn’t enough for the circuitry, or alternatively the VIC chip or something along the address bus decoding is busted. I’m guessing it has more to do with the power supply, since probing with a scope revealed that the TTL glue logic responsible for the VIC address decoding is stuck at around 2 volts.
The glitching causes interesting visual patterns though!