Problem

Solid green/brown screen, no sound.

Diagnosis

Breywood (aka Shackled) shares the same CPU board as Last Mission but uses a different video board. There are two 6809s, a 6502 for sound and a read-protected 8751 that serves as copy-protection and handles coin inputs.

As I had just finished debugging another 6809-based game with my logic analyzer, I hooked it up to the 6809s to see what was happening. CPU1 appeared to be stuck in a loop, having read back a bad value from the 8751. Time to see if the 8751 is actually running…

The 8751 has its own reset circuit, and has an active-high reset input:

The voltage at the RST pin was >4V, which is logic high. I swapped in a new capacitor and voila, the game sprang back to life (with no other faults!)

Fix

Replace 10µF 16V capacitor at C38.

Philip Bennett