NSM Hit 120 scans but does not trip

Hi,
Just bought a faulty NSM hit 120. When a selection is made the carriage
makes two return scans but does not trip. All cabling looks good, what
voltages are marked look fine. If I manually trip by moving the relay in the
control unit whilst in scan it will play ok. I have no manuals, but from the
looks of it the memory may be a core store similar to 70`s seeburgs which
I'm familiar with. Can anyone give me any pointers, websites with scans,
schematics etc to help me understand the write / read system of this
machine?

Dave