GPSNAV problems

I have a problem with my GPSNAV (model 20 I believe, with the external
antenna). The GPSNAV output to the screen works fine, directs me to the
waypoints etc. This shows that the GPS engine is working.

However, the output to the PDA via the serial port, and the Datacom output
to the L-Nav seems to be doing nothing. The cables are definitely OK.

I am unable to find a .cai trace on the logger after a flight, output to
the PDA is hugely intermittant- it works for a few seconds at most over a
whole flight. The L-Nav reads GPS (Wait).

Has anyone else experienced similar problems? Dickie Feakes, the UK dealer
seems to think it could be in the contact pins, but it seems odd as it is
experiencing issues with NMEA output on 2 different connector types.

The logger was overhauled with all internal parts (except the power board)
replaced roughly 3 years ago.

Any ideas on how to fix it?
I am UK based.

Cheers,
Shaun