Open/Close and Zero/Top switches are common problems:
- what are they?
- correct adjustments
The site usually says you should adjust the stationary blades, not the moving blades. This is one of the exceptions.
The non-adjustable things are the zero/top pins. It may be necessary to bend the moving blades to position them correctly at step 1 and the penultimate step so they are barely touching the pins, then bend the stationary blades for proper switch contact action.
Before bending the moving blades, make sure the two switch stack bolts are snugged down. The bakelite spacers shrink with age, so you want a tight stack before adjusting the blades.
The schematic usually refers to these switches with text like "open at zero timer unit" or "selection feature unit close at top". That description tells you the stepper unit to look at, and when the switch is operated. There's usually no other information in the manual.
"Zero" means the reset position of the unit. "Top" means the last/highest step the unit can reach due to the notch/missing tooth in the ratchet.
Stepper unit ratchets may have either/both/none of the pins. When they have both, some of the switch blades are pushed by one pin, the rest are pushed by the other. No switch blades are operated by both pins.
The typical problem is just switch adjustment and cleaning. Cruddy switches is easy. Contact can be slightly off due to wear, or way off due to intentional misadjustment.
With no information in the manual, you just look at the switch blades the pin is pushing and see if the contacts make sense. On this unit, there's three open at zero switches and no close at zero switches, so look for a reasonable contact gap.
The zero switches and the direction they move is indicated with the purple lines. The other switches on the left are top switches, and they should not move when the zero switches move.
You're looking for good switch closures. The easiest thing is to push in the step-up coil plunger and let it out slowly. Watch the contacts on the moving blades...they should touch the contacts on the stationary blades then you see the stationary blade shift a little (overtravel).
Overtravel creates a contact wiping action that helps make a good mechanical connection. Notice here that the stationary blades are thicker, so they aren't going to bend a lot after the moving blades contact them.
What you definitely don't want is the contacts barely touching. That's the most common problem, and it's an unreliable connection. "It looks ok" isn't good enough.
The zero pin can/should be barely touching the moving blades at step 1 (orange arrow). It can be slightly touching or have a tiny gap, but you don't want the pin to be holding the moving blades away from the stationary blades.
Penultimate step? ... ok, fine, the step before the top step. The top pin can be barely touching the moving blades, but should not be pushing them and affecting the contacts.
A common operator hack was the bend the "top" moving blades so a switch opened at the penultimate step ... or earlier. Often that switch disconnects the step-up coil on the unit. The result...the unit can't step to the top. Inconvenient when that means you can't get top scores or certain features.
The pin has pushed the moving blades and opened the switch contacts. This unit has no "close at top" switches.
The zero switches aren't affected by the moving blades.
The description above is the ideal adjustments. Practically, it doesn't need to be that perfect. The point is to make sure the switch contacts open/close with good overtravel action. Barely touching contacts will cause you grief.