Some these things don't have a start capacitor nor a centrifugal switch, they are just a reversible PSC motor. I have had trouble calls before where flies (or other insects) get into the contactor and cause failure to make contact, either on a power pole or on aux contacts for control circuit. I'd probably check that out first since it is pretty easy to do.
Looked up the wiring diagram, does have a capacitor, probably is a PSC motor like you said. Looks like solid state control, and the motor
terminates to a pc board, so it is controlling the reversing functions.
I think that's the schematic for my unit. Attached is what I have. It's an MJ-5011 model MT. This current unit is a replacement for the identical unit that was also acting erratically for years. It would get 'stuck' open and not close, or vice versa. A little shove in right direction would usually get it to roll and then it might not do that again for weeks, or maybe the next day. Totally erratic. So we replaced it with a brand new unit of the same model and the new one is doing similar things...it 'stalls,' refusing to roll either open or closed, it can happen in either position, and it also has another trick: it will start to close. stop halfway, another press of the remote and it will close another 2' or so and stop again, and another press of the remote and it will reverse itself and go back to fully open! The only PC board I see in there is in the remote receiver, which may be emitting spurious signals. How would I check it? It looks like there are three connections from the radio receiver to the motor control section, labeled R1, R2 & R3. I've seen the installer short two of these and the gate opens (or closes, as is the case). Regarding the starting capacitor, I had changed that on my original unit and it made no difference, in fact I'd say it worked more erratically than with the original. so I put the original back in. The current unit was manufactured just over a year ago, Feb 2019, so I doubt the starting capacitor is the problem. Whatcha think? And thanks for your input, everyone.
The capacitor is a separate piece, inside the control box. I changed it on my original unit which was doing the same 'stall' business, and it didn't improve anything. The current unit is the exact same model, MJ-5011 model MT, but only a year+ out of the factory. I know it's a roll-up door actuator, but here in Puerto Rico these same units are used extensively for rolling gates and the installer says he's never heard of this same issue before and he's installed countless number of these units for rolling gates. I'm up against a very strange problem. Your help is much appreciated. Thanks.
We are on a fulltime Tesla system and the voltage is pretty constant. I've put a Kill-O-Watt meter on the unit and during normal operation, the unit draws ~4.5 amps, voltage drops from 117 to 112 and slowly climbs up until the gate finishes its operation. When stalled, you can hear the relays click, you can hear the motor hum, the current draw is a ridiculous 8+amps, voltage drops to 103 or so, but the motor does not start turning. A healthy shove in the right direction sometimes gets it to roll. Whatcha think?
Brake is shown on the diagram he posted, that could be an issue as well.
