Hayter 749 problem

[robin banks]

A friend bought one of these finishing mowers at an auction and didn't try it out for a long time. Asked me to get it going. It seems to work apart from 2 of the 7 cutters don't spin. They are not seized. They are driven by hydraulic motors.
Am thinking it may be a valve issue. There are 3 pipes going to each motor. 2 normal size and a very thin one. So I suppose its a flow and return and not sure what the 3rd is.
Any ideas where I should look next time I am at machine.

 

[davidroberts30]

3rd small pipe is a motor case return

 

[agrimax]

I'd guess that machine will have a cutout valve on each cutting cylinder so when it's lifted up from cutting position,it stops the motor. May be worth looking for a valve/button that hits against an arm when lifted. Could be stuck shut. Or another thought...if it has solenoid valves,could be faulty solenoids or micro switches that open or close when lifted/dropped.
@raiderz ...Are you still about? Can you shed any light on these?