My (Chamberlain/Liftmaster) Elite Roboslide gate operator recently stopped working.  Several weeks before failing, it would stop about 1' after opening because it would hit a ~1/8" jog created between the rail (ground settled creating a change in height).  The problem was temporarily solved by just pushing the remote again.  Now when I would try to open/close it, it would move about an inch before stopping.

I did some troubleshooting and noticed that the relays on the circuit board were chattering.  I figured that the internal relay contacts were worn or that the signal to trip the relay was weak/bad.  After verifying that the connections were good, there were no obstructions/excessive drag on the gate, and that the motor was still good (by using a separate power source directly to the motor), I went and ordered a new circuit board (Q206).  

Unfortunately, the new circuit board exhibited the same relay chatter.  I was trying to do some research online but there isn't much information.  I came across a post on amazon.com about a load sensor inside of the motor.  I am not that familiar with electronics and don't understand why there would be a load sensor inside the motor when it would make more sense to have it on the circuit board.  I don't want to spend money on a new motor like I did the circuit board only to have it not work.  Please advise.

Does it open/close freely when in freewheel mode?  I know ours has a protection that if it hits anything it will stop.  We had a couple wheels that needed bearings and it was doing the same thing.  Also adjust the chain and grease everything.

The gate doesn't have a freewheel mode but, yes, with the chain disengaged, the gate does slide freely without any binding aside from momentary resistance when it hits the 1/8" jog between rails.  

I replaced the original roller bearing wheels with ones with sealed ball bearings a while back.  I actually just replaced the chain and idler pulleys because the chain was rusty and the pulleys were worn.

IIRC, the overload/heavy gate LEDs do not illuminate when I try to open/close the gate.  However, sometimes the overload alarm will go on if I keep trying to open/close it and help push the gate.  I also tried to disconnect the backup battery and accessories (remote, electric eye, etc) and it didn't make any difference.

that has a low voltage dc motor correct?
Miracle circuit board?

if so take a look at your dc power under load.  I bet its dropping allowing the relays to chatter off and on.
Sounds like you have a handle on the gate moving freely with little resistance which is important.  You are correct the overload led would illuminate if that were the case
Also make sure all you connections are tight.    Take connectors off batteries close up the connectors and put back on batteries.  
9 out of 10 times relay chatter is bad power


Edit:
I pulled the manual and took at look
look at the voltage under load
check all connections between battery and board
safe to bet there is no sensor in your motor
still thinking its a power problem
turn the reversing sensitivity counter clock wise to make it less sensitive ( you  can adjust for safety after you get things running ) I know the light didn't come on
if power is good take a look at the close limit switch - does this happen as soon as it comes off the close limit switch?
unplug your ac power adaptor feeding the board - it will probably die out totally due to the lack of help from the ac ( should run on batt no problem )


bet you $10 its a power problem

My 2c ...
If there is a safety eye/beam that bounces off a mirror (for example) they have to line up so that the beam is actually reflected back.
There is a bit of "wiggle room" in the aiming process. However, sometimes when it is lined up, it is just barely line up. Therefore, when the gate starts to roll,
it can throw the beam slightly out of this range of alignment.
If this could apply to your system, I would make sure that a tiny movement of the sensors isn't throwing them out of line.
Let us know what you find out.

Stay safe

the reversing input only works when the gate is closing - he said it happens when he opens the gate