Unfortunately using a scope is something I've never done before although would give it a try. I have swapped out the vias and even used a different via from a spare vic20 and sadly its the same.I suspect that the VIA has the shift register bug. The simple tests described in the fault finding section cannot readily detect this fault and it usually needs a scope to confirm the incorrect number of shift register pulses.
I assume you've checked for continuity between the VIA pins and the User Port. Specifically you need to check pins PB0-PB4 and CB1/CB2.
I only get ?card with the whole unit from the user port removed after power down and the bbc restarted.
Does anyone know a reliable place to get a user via that wont have the incorrect number of pulses? At least then I can rule the shift register bug out.
Also anyone recommend any beginners multimeter/Oscilloscopes? (Athough an Oscilloscope, that's probably a step too far for a beginner?)
Statistics: Posted by Coastered — Tue Jul 01, 2025 8:16 pm