> > Why do you assume the readings aren't correct if they are now stable? I'm now a > > little unclear on what exactly the problem is that you are trying to solve. > > Because on some PCBs I obtain different values from the ones already in MAME
the LM1881 is not the best option. use a EL4583 sync splitter from Elantec and make the circuit shown in the pdf for the dev board they also sell. add a low-pass filter and you'll get the same readings as MAME (+- 2.0% depending on your equipment)