Thanks for the reply skiddins,
I just pulled a 4.8V Ni-MH 150mah battery from a Losi Micro T.
Plugged it into the BD (pins 4 & 5).
Problem solved and everything working fine.
But!!!!
I still don't understand why I have to do this in the first place because it's been working perfectly up until last night?
I noticed when connecting everything up using the internal booster the transponder light comes on but it's really hard to see and fades away to nothing.
The AMB transponder requires between 4 - 8VDC
Short term I'm going to have to use the Losi battery if I want my laps counted but would really prefer to run a booster, what's everybody using these days?
Maybe a small 7.4V Lipo would work well?