Spindle rotates only clockwise (M3 works, but M4 does not work)

Dear guys,

I have a Fanuc turning machine, Oi mate TC.

The spindle rotates CW when I run S300 M3. But it does not rotate when I run S300 M4.
So the spindle only rotates clockwise and it does not rotate counter clockwise.
I checked the (M3 and M4) contactor. It works when running M3 and M4 but the motor only response to M3.

Any suggestions?

Faulty contactor for M4. Check output with a voltmeter.

Cheers
Roger

Never seen a Fanuc use forward and reverse contactors...this must not have a spindle drive?