Rotax Flydat Screen error

I have no experience with that particular unit, but from general electronics experience I would suspect a couple of things: either a bad solder joint that's causing intermittent faults or some other component that's near failure and is showing temperature-related effects.  I might also suspect a failed electrolytic capacitor that's causing power supply instability but I'd expect that to be a constant problem, not intermittent, and not affecting only the display.  Either way, I'd say it's going to need some time at an avionics shop.

It looks like you have the first version of the FLYdat instrument, which was replaced by a new version some time around 2004.  Even the new version appears to be out of production.  I can't find anyone selling them and the only other thing on TL Elektronic's website is a press release from 2015.  It's not in their current product catalog, so finding a replacement if needed could be difficult.

Sounds like you might have a good excuse for a panel upgrade!

That's a problem with the contrast control to the LCD. The contrast is normally set via one of the following methods:

1. A voltage set via a small potentiometer, often found on the circuit board or adjustable through a small hole in the case.

2. An internal temperature sensor is used to automatically adjust the contrast as the temperature changes.

3. The software in the microcontroller adjusts the contrast.

Ultimately all methods just generate a DC voltage that controls the contrast of the LCD.

I f it is method 2 then I would try adjusting the pot in case it has a dirty wiper. In the other cases I would inspect the PCB very carefully for bad solder joints. If it is none of these then it could be a faulty LCD which you can probably replace, it looks like a standard 2-line character LCD.