BBC Model B (was a Model A) Issue 2 - serial and cassette don't work.
Checked the serial ULA in another Beeb and it was fine. Checked for +5V and -5V and discovered the -5V line was missing. I did have sound, so I wasn't expecting this supply rail to be missing. Using the Toneohm I found a broken trace underneath IC7 where someone had levered up the socket instead of the IC and destroyed the -5V rail.
Running a wire from the -5V rail entry point to pin #11 of IC35 solved the problem and now the cassette and serial are working.
Checked the serial ULA in another Beeb and it was fine. Checked for +5V and -5V and discovered the -5V line was missing. I did have sound, so I wasn't expecting this supply rail to be missing. Using the Toneohm I found a broken trace underneath IC7 where someone had levered up the socket instead of the IC and destroyed the -5V rail.
Running a wire from the -5V rail entry point to pin #11 of IC35 solved the problem and now the cassette and serial are working.
Statistics: Posted by maniacminer — Fri Jun 28, 2024 12:34 am