What are your symptoms ? Completely dead ? Intermittent ?
I have the rectangular display, but never opened it.
While the rotary encoder is mounted pretty flimsy, the RJ socket seemed to be mounted quite well in the backside.
I think that the RJ connectors in general are pretty poor connectors, but I would be very surprised if your problem would be a matter of broken RJ12 solder joints (unless you can clearly observe the RJ12 socket being loose)
Did you check the wiring, like the RJ12 plug ?
In my experience, the vast majority of glider electrical problems are wiring problems, particularly if you are kicking wires getting in and out of your glider.
You can check your display with the upload cable.
If you don't have (a friend with) the upload cable, you can easily build one from this example.
https://sites.google.com/site/threeu...terfly-display
You can also use a standard USB-to-RS232 serial cable (not USB-to-TTL) if you take care of the 3.3 Volt power supply separately.

3U