I recently got a Cinema Products J4 zoom control that only seems to run the motor at one speed. The motor(s) were I think used for a 35BL I. I wondered if the system had been tweaked with extra torque for that, but I don't think it can explain what I'm seeing.
The speed control pot in the electronics / battery box was corroded so I replaced that but it didn't change anything. In fact the motor behaved the same with the pot removed from the circuit. I measured V on the black/red wires going to the motor and pushing / pulling the thumb switch I got ....
- push ....12.5....12.8V
- pull ....-0.2.....-0.35 just after the start click, then staying at -0.35.
I had a quick look at the thumb switch internals. Thought I might leave it to an expert. I'm meeting one for another job soon.
Does anyone have a srvice manual or circuit diagram for the J4 zoom control? Any thoughts about what's wrong with it?