The other day I was setting up one of my new controller boards; and part of that process involves turning the trimmers to their maximum anti-clockwise position; once the board was powered up, this one particular trimmer which was used to trim the LCD contrast didn't seem to make any difference when adjusted; So I knew instantly the trimmer was at fault so I just replaced it with another and it worked perfectly.
The problem seemed to be that when I initially quickly adjusted it to it's maximum anti-clockwise position, the wheel gear cog must have gone too far, and then wouldn't re-engage.
I've never experienced this before but might be something to bear in mind. Luckily the LCD contrast made the screen visible; but had it failed in the clock-wise direction of turn, the LCD would have been blank; and I would have certainly had to fire-up the scope to find out what was going on.
