had it recently
Turned out to be the collective position potentiometer, or something like that. Took our mechanic about 4 hours to replace the faulty one. It is located under the floor inside the right stowage compartment near the bulkhead, front end. It is a small part but a bugger to replace. He had to remove the O2 system tank and hardware first and then remove the faulty unit and solder all the wiring into the new one.
Hope that helps.
Cheers