Spektrum DSM dodgy neutral

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So I am setting up a Futaba 3VCS with Spektrum Pro DSM module and SR300 receiver in a 10th buggy.

I have turned on the transmitter and calibtrated the speedo and this is working fine.

Problem is if I turn off the transmitter the speedo neutral is about 20% forward.

Anyone any ideas what that's about? and how can I get it to sit at neutral when the tranny is off?

I believer the failsafe function of the 3vcs only works in PCM mode and as I am using DSM I am in PPM mode which does not seem to have a failsafe setting???

I've used a 3vcs with various other modules for years and never had this before.