Apologies if I'm missing something but I couldn't find anything in the service manual, or the extract you posted, which explains why pin 5 of IC 27 is patched to somewhere in the region of pin 39 of the user VIA and pin 1 of IC25 is patched to somewhere near pin 11 of IC 7 on Issue 2 boards built by ICL and not those built by Cleartone.There is a lot of detail in the Acorn BBC Micro Service Manual
I'm sure that a specific and definitive answer to that question would reveal some details which are not covered by the service manual.
Statistics: Posted by NJ_ — Thu Jun 19, 2025 8:28 am