I have zero repair experience on Beebs.
But, IMO:
- the VIA is unlikely to be the culprit
- the fact that the Serial ULA at least half-works (cassette relay operating correctly) suggests that the fault may be elsewhere
Possible causes, again IMO:
- bad MC6850 ACIA
- bad analogue circuitry on the cassette input
- bad DCD capacitor on ULA pin 15
Do you have a means of testing the RS423 interface (which would also be disabled by a bad ACIA)? Do you have a way of getting software onto the machine other than typing it in? There are some tests that can be done on the ACIA even without any RS423 hardware.
What do you get if you type
> PRINT ?&FE08
on boot?
But, IMO:
- the VIA is unlikely to be the culprit
- the fact that the Serial ULA at least half-works (cassette relay operating correctly) suggests that the fault may be elsewhere
Possible causes, again IMO:
- bad MC6850 ACIA
- bad analogue circuitry on the cassette input
- bad DCD capacitor on ULA pin 15
Do you have a means of testing the RS423 interface (which would also be disabled by a bad ACIA)? Do you have a way of getting software onto the machine other than typing it in? There are some tests that can be done on the ACIA even without any RS423 hardware.
What do you get if you type
> PRINT ?&FE08
on boot?
Statistics: Posted by Diminished — Fri Jul 11, 2025 10:52 am