Hi uj
are these 3 to 8 credits stepped down (AAA) at ONE time - within a quarter of a second ? OR: (when starting a game) BBB: ONE step down - but then faulty: after some time another step down - after a some time: another step and so on ?

If You have BBB: we must look in the schema.
If You have AAA: the spring (wound around the axis) is TOO tight.

Stepping down: the force to turn the wheel comes from the spring (wound around the axis).
Stepping up: the Step-up plunger is pulled (magnetic force) --- the Coil quits pulling: NOW the spring "pulling back the step-up-plunger" does the work / step-up. Greetings Rolf

Hi uj
when having the "AAA"- I'd say: The spring around the axis is way too tight. Look here: http://www.planetarypinball.com/reference/partsmanuals/WMS_Parts_1969/index.html#/14/zoomed --- the gear (wheel) and some kind of a "hook" and an arrow from text "10A-244". Hidden by the two stretched springs there is another "kind of a hook" --- when the pin wants to step down ONE step: These two hooks are kind of "wiggled" so the wheel does ony step down the wanted step. See the "spring wound around the axis" (?) When this spring is way too tight: brutal / rude force --- the delicate wiggling cannot take place.

Again: To step up the Unit: The coil on the right of the picture pulls-in - moves an arm - coil lets go - spring 10A-228 pulls the arm back and the wheel is stepped-up one step.
The force / energy to step down the Unit: The spring wound around the axis.
This spring has ONLY to be tight enough to do the step "Position-1-Replays down to Position-Zero-Replays". By stepping up more and more replays: The spring wound around the axis is getten tightened - to step down from (lets say) Position-19 down to position-18: There is more energy in the spring than when the unit has to do the step "1 down to Zero".

Manually step the Unit down to position-1 (or -2 or -3) --- then unhook the spring wound around the axis - turn it around to un-tighten --- try - un-tighten some more turn(s) --- only needed: Enough tension in the spring to securely step pos-1 down to pos-Zero. Greetings Rolf

Hi ~ja
my theory is "The spring wound around the axis is way too tight", JPG in post-5: bottom-left the "new spring" then "upwards rightbound" an arrow - the axis - further "upwards rightbound" --- see the "end of the spring hooked-in on a a solid place": Unhook there and HOLD THE SPRING / END of the spring. Carefully let the spring make a turn "un-tightening" - then hook-in again.

You may do this SEVERAL times --- write down "how many turns You have loosened".
You can loosen - loosen - loosen - it only has to be enough "tension in the spring" to securely do "Step pos-1 down to pos-Zero". Greetings Rolf