From someone who has no idea how these work it would be appreciated if you could explain.
With pleasure, J.
If you look at the pictures you see two solenoids with ratchet wheels on one side, a complicated gear thing in the middle and a switch disk on the other. The PS device is functionally identical except its more compact and instead of a switch disk, it has two microswitches and a cam. Looking at the gear box, one ratchet is geared to the top bevel gear, the other is geared to the bottom one. In between is a small gear on a short shaft. In the middle of that short shaft and pinned to it is another shaft at right angles that drives the wipers, or in the PS case the cam.
Let's say a solenoid clicks the ratchet attached to the top bevel. The bevel turns a small amount and that turns the small gear, but since the bottom bevel didn't move, the small gear has no choice but to roll around between the two, turning the center shaft and the cam a small amout. When the other solenoid clicks the same thing happens, but in the reverse direction.
One solenoid clicks every time a coin is inserted. The other one clicks every time a coin is paid out. Thus the position of the small gear and cam reflects the difference between coins in and coins out. When more comes in than goes out, the wiper/cam moves one way, and when more is paid out than comes in it moves the other way. If you look closely at the photo of the ratchets you'll see they have numbers written on them - that's the number of teeth. Obviously a ratchet with fewer teeth turns its bevel gear further per click than the one with more, so for equal numbers of "ins" and "outs", the cam moves steadily towards one end of its travel until it operates one of the microswitches. Let's call this the "tight" switch. Other circuitry in the machine operated by the "tight" switch cuts off some of the payouts by preventing the reels stopping on them. So now for a while there are more "ins" than "outs" and the cam moves the other way, off the "tight" switch, and the blocked payouts can be hit again. In the event of a long run of losers, the cam gradually works its way all the way back and operates the other microswitch - let's call it the "loose" switch. More circuitry then operates to enable additional wins, and the resulting payouts work the cam back off the switch to the middle.
The overall result is that the payout percentage of the machine is regulated to the ratio of the number of teeth on the two ratchets
To anyone familiar with playing PS machines, it should now be clear why the machine plays normally for a while, then goes into utterly tight mode where the same losing combinations show up game after game, then becomes normal, then gets so loose to the point where if you don't hold a likely combination, it will probably come up on its own within the next few games. Normal play, unaffected by the regulator, was probably set different from the regulator percentage in order to give the game this cyclic variety, because if they were the same, the regulator would spend nearly all its life in the middle region and hardly ever hit the microswitches.