Screen saver & TT Nav 5

[andy_s_king]

Hi all
having upgrading my ipaq car cradle to a powered one (for better sound) i now appear to be bugged by the screen saver appearing whilst running Tom Tom Navigator 5.1.  This never happened when running of battery - only now i'm running from cigarette lighter (AC).  The screensaver kicks in if i'm sat at traffic lights or travelling down the motorway i.e. the screen is moving!! so why is it coming on?? I have an IPAQ 4700 running Windows mobile 2003 SE (V4.21.1088) I can't seem to find anyway of disabling the screen saver - can anybody help???

TIA

Andy