Issue: On JD, even after a full flipper rebuild, the flipper fingers feel weak.
Solution: Checked for correct components and correct coils, ok. Measured voltage coming to coils, which should be around 70v dc when no flippers are pressed - only got around 55v at the coils.
On JD, power for the flipper fingers is generated via a bridge rectifier (br1) on the fliptronics board, with AC power coming directly from the transformer's secondary winding to j901. Measured the bridge's diodes - all ok, voltages at j901 were ok as well.
Looking at the board, C2 was missing, which Williams did on some boards, and installed on others. Installing C2 on the board (i used a 100uf 100v axial capaciror) bumped the voltage right up to around +68VDC. Flippers were now snappy and powerful. Issue resolved.