Diagnostics (VIC-20)

it is easier to group basic problems with common causes on the vic 20 rarely will there ever be trace damage it is almost also ic failure, and the failure of specific ics gives common output problems no screen this indicates most commonly a bad power supply, fuse, regulator, or a dead short all in all preventing the system from receiving power it can also be a bad vic chip (under the metal can near av port) less common could be your tv, video cable or video circuit on the computer black screen if you get a valid video signal but all black this is usually 6502 cpu (ue10) kernel rom (ue12) basic rom (ue11) bus transceiver (uf8) solid color screen (blue / red / yellow / cyan) if you get a screen with no border and all a solid color, it's almost always a bad vic (under the metal can near av port) user / cassette port if the user port or cassette ports are not working, this is usually the uab3 (mos 6552) serial port if the user port or cassette ports are not working, this is usually the uab3 (mos 6552) or the ub4 (7406) no keys working if it isn't the actual keyboard, it is usually uab1 (mos 6552) by the keyboard connector joystick issues if not the actual joystick or physical port, this is usually the uab3 (mos 6552)