The relevant part of the schematic is:
with of course a 1k resistor for R42. Measuring the following points with the other multimeter probe at a ground point should give you:
Left end of R42: 12V
Right end of R42: 4.1V = pin 2 of U4 and pin 3 of RV3
Pin 3 of U4: 0V
Pin 1 of RV3: 0V
Pin 2 of RV3: 4V after trimming = TP1
If you don’t have 4.0V at TP1 then either:
- You don’t have 12V going in.
- You do but you don’t have 4.1V on pin 2 of U4 which means that voltage reference is faulty or misconnected
- You do but you don’t have 4.0V at TP1 which means the trimmer isn’t set right, it is faulty, or it is misconnected
I don’t see any other possibilities.