Hello! Trying to repair a Liftmaster 3850. Issue started with the door opening a foot or so and then closing for a couple of tries, then finally not responding at all. I was told that the flashing error code suggested either the travel module, or I needed a new logic board.
I have two of the identical openers in my garage, so I experimented and swapped the logic boards between each of them - and oddly neither opener would run at all. So, I swapped them back to their original spots and the good opener works fine again but still nothing from the bad one.
So then I replaced the travel module with a brand new one and still no activity. Lastly, I purchased a "tested" used logic board and put it in the bad unit and still won't operate.
The opener powers on, the motion lights respond, but pressing the button to set the travel limits and nothing happens. I can hear a faint electrical noise like it's trying to do something for a second but that's about it. Since taking out the logic board and putting it back in there is no more flashing error code to reference, I just can't get the motor to move the door when trying to set the travel limits. I should note the battery backups are dead so I disconnected them years ago, not sure if that would impact this or not.
Since I have two doors and openers it wasn't critical this get fixed right away so had some fun trying to DIY it and learn a thing or two but I'm about to give up and finally get a new one installed, but is there anything else I missed here?
