The error appears both on the bench and in the machine. The error first disappeared when I tried tracing the RST line as the 6809 was being held in reset. Whilst tracing this signal the board sprung into life. It then worked for a short time in the machine but at the next power cycle the error returned. As it was whilst checking around the 7414 that it came to life, I swapped that for a new one. I've now changed also the asic and the 6809 but the error persists. Once the board springs into life it continues working until the next power cycle. Tomorrow I'll try resoldering the whole board in case there's a hairline crack somewhere.
Mike.
Edit, why is this being posted with a tiny font size? Just had to up it to 12 to see it.
