CIRCLE WITH A DOT

I went down to @icm to work on Miss Piggy, their PDP-11/70 system. Any instruction that touched memory would wedge the processor (though front panel accesses worked OK). Brought along my KM11 diagnostic set to help diagnose the issue and traced it down to a faulty microcode ROM (one of several early bipolar 256x4bit PROMs in the system). We had a spare ROM board so we swapped that in; chip-level diagnosis will happen at some later date. The system boots 7th ed. UNIX once again!