When I turn the game on (from power off) it starts, resets score reels, releases the ball to the ball lifter and plays and scores normally.
When the first ball drains it does not subtract the lost ball (stays on ball 5) and does not release the ball to the ball trough lift mechanism. If I manually release the ball and play it, scoring is normal, but draining the ball again does not subtract a ball.
If I then start a new game it will reset, but not not release the ball to the lifter, hence I can't lift it to the trough to plunge it into play.
If I turn off the game by the slam switch, then restart, all is fine, the ball releases to the lifter and plays normally until the first ball drains, then it does not subtract the ball, release the ball to the lifter, etc.

Any ideas? This happened for a while a year ago and then the problem somehow disappeared with no help from me.
I do have schematics but have trouble following them.

For those of you following along with a similar problem:the machine fixed itself! Here's the gist of what I'd sent to HowardR by PM before I got his response about the four switches above...

...I started the machine to take another look, the 100s reel hung up on reset, I tapped it and both the 100s and 10s reset to zero, then the game worked fine, ball count subtracted from 5 to 4 on drain and the ball released to the ball lifter, played several games with no problem...

Coincidence with the score reels? Got me. This happened once before a year ago, if a next time I can see if the F relay locks on and then check the switches in the diagram above. Can't check them now 'cause they work properly. HowardR, thank you for all you do on this forum.