Just had the same issue with 3 master control panels, mark the position of the trimmer on board 2, use contact cleaner and clean by turning back and forth a good many times and reset back to its original position,obviously replacing trimmers is always better but requires more skill, also replace the 47uf 10v cap next to it, best to just snip the cap and solder to the orinal legs of the old one as it takes very little heat to solder it in, put solder on the legs of the new cap first.

another much harder fault I solved with these is continuous flashing display even with new batteries, hours of measuring couldn't find it, turned out to be the Pelco type micro switch on the wheel, it is supposed to bounce back very slightly to the center of the up and down contacts, if cleaning and freeing up the wheel doesn't cure it, replace the switch itself as the flex in the center contact is no longer strong enough to pull it back into the center after volume turn, when it sits making contact with either contact the result will be a flashing display,

this applies to both mcp5500 and mcp6500

hope this helps.

jason

Thanks Jason but the R117 is for setting the 4,75V , that should have been easy to measure something is wrong on that power setting?

I will check this .

Thanks

Fred