We are restoring two Space Shuttles side by side. We now have them playing but noticed that one machine has better flipper strength than the other. The kicker is, the one with brand new coils is the one that is weeker. We measured voltage at the coils and found to have only 38 volts at the flippers. Then we measured the other machine. It has only 40 volts. Now I know it should be close to 50 and both machines are reading low at this point.

We have already replaced almost all of the caps on both power supplies, and installed the new and quite slick little board with bridges and caps to replace the big capacitor and 2 bridges in the lower right corner of the back box.

Question: What else can be causing our low readings at the flippers? One machine is 38v and the other reads 40v.

Welp, turns out that I had my grounding lead on a not so good spot. When I ground directly to a cabinet ground both machines have a solid 65 volts.
Only mystery that remains is that inspite of a new sleeve,coil,spring and cleaned flipper shaft and guide I still have one somewhat weak flipper. I am wondering if the new coil may be a dud. I cannot detect a mechanical bind whatsoever.... free as free.

Thanks guys! I am betting you are correct. I was just reading about all the arcing (plus witnessed) those switches do on that particular flipper design. I believe a few fresh switches are in order.