I have a JLG 40F, circa the 80s with a Wisconsin gas motor and I am pretty sure Berta valves, I am looking for ether the proportional controls or something to replace them. Each one has a variable resistor (pot) and a micro switch, I think the switch is to disable power to the pot when in the neutral position. I am having drifting issues with the swing, it drifts slowly when all controls are in neutral but gets much more aggressive when using the lift or drive controls. Mine are so corroded I doubt I can even get them apart.
Oh man, I have to really dust off the cobwebs in my head, haven't worked on a 40F in well over 30 years. And yes, you're correct, the PQ controller for the Bertea (pronounced Burr Tay Uh) valves have a microswitch to kill power to the controller circuit board/pot when it's in null position. For that reason, since the outputs of the controller would be dead, if you have movement of a function when it's in null then the problem is the valve, which is not unusual for Bertea valves, they had that problem while relatively late model, probably even worse now 40 years later. Bertea valves were very finicky, and they require perfect cleanliness internally, no dirty oil, no contaminants, no debris. Back in the day when a machine had that problem, most times it could be fixed by simply taking apart the valve components of that function and clean all the components, but you stated that might not be possible with your corroded unit. So, if you really wish to keep that old machine running, yes, updating to a different proportional valve would be most desirable, but what that would be I have no clue, but it would definitely involve replacing all the proportional controllers as well.
The deal is the micro switches are evidently not working, I see power to the pot all the time (on all three controls), if I switch to ground mode which just uses momentary switches (and I think some fixed resistors) it does not drift. I REALLY would like to have one of these controls in hand before attempting to rebuild one of my controllers, they are pretty bad, without a doubt the terminal board/s would have to be replaced as the terminal screws will never turn again, that probably would bot be a big deal as they look like common circuit board terminals to me, it's the rest I worry about. I can put a bungee cord pulling against the lever in the neutral (locked) position and it drifts very little so I would rather put up with it than trying to repair the control stick and wind up with a machine I cannot use. This thing is a real challenge as I bought it out of a scrap yard and I was not the first one to jury rig the thing and I have been doing that for 20 years on this machine. I have a Genie 85S but it is way too big to use inside my shop
Those PQ controllers are very old now, don't know how available they are. One thing you can try is contact Hindley Electronics in Ohio. Back in the day they would rebuild those controllers if you send them in to them. It's worth a try. > https://hindleyelectronics.com/