Cambridge L-Nav problem -- runaway vario

At 17:02 07 July 2014, jherzog wrote:
I have a nagging, recurring problem with my trusty L-Nav. Occasionally
when I power the unit on, the lift tone sounds constantly, and the vario
display is pegged at maximum lift (10 kts).

Long time ago but I had a similar problem. Mine tended to stick at a random
figure, say 2kts up and would often occur after I'd done a pull up. The
LNav would then continue to work but around the new datum - very difficult
to fly when you have 2kts of audio as your datum! On the ground when the
problem occurred, even taking all the pipes off made no difference and I
seem to remember the fault lay in a sticking airspeed transducer. Don't
know if you can get these replaced any more.