Tamiya Sherman sound unit problem in 1/6 scale Sherman

[markrussell]

Hi All,
I have recently purchased a 1/6 scale Armortek Sherman with a Tamiya Sherman sound unit in it. When running forward the engine sound is all ok and revs up with the throttle but when running backwards there is no engine reving sound just the engine idle tick over sound. Also when you turn there is no enging reving sound just the idle tick over sound. Any ideas anyone please?
Kind regards,
Mark

[markrussell]

Hi how do you calibrate the dmd unit as I have no instructions?
Thanks,
Mark