I recently aquired a few Robocop PCBs, and this particular one seemed to be working fine at first glance. Eventually however, I realised that certain sounds seemed to be missing from the attract mode.
In particular I noticed Robocops speech as he rolls off the Prime Directives was not there. A closer look playing the game revealed further sounds missing, like the groans from the enemies as you kill them and others.
I then realised that is was just the ADPCM samples that were missing.
So I looked at the CPU board where most of the final digital and analogue circuits are. First I checked the DACs and found no samples present, so went further back to the large YM2203 sound chip. I probed pin 19 of the IC and would have expected to hear the samples here, however I heard nothing except static.
I was able to determine that the ADPCM samples are stored in the EN02 ROM, so I popped this into an eprom reader and checked the content.
The eprom was corrupted, so I burned a new one and the samples were restored.
Another Robocop saved.