The bonus unit counts down to zero when the ball drains. When the bonus unit reaches zero, a switch on the bonus unit closes to energize the outhole relay. That causes the kicker to kick the ball out.

The bonus unit is supposed to step up to 1000 points when the ball is kicked out to the shooter. Since your bonus unit isn't stepping up (that is, the bonus unit is stuck at zero) the outhole relay stays energized and the kicker just keeps on kicking. That's why the problem stops when you manually step up the bonus. You are doing by hand what the machine is supposed to be doing automatically.

Does your bonus unit step up (that is, add bonus) during game play when you hit a 500 point & bonus advance target? If so, then the problem is likely a dirty/mis-adjusted switch on the outhole relay, or a broken wire at the solder lugs of this switch. This is a normally open switch that needs to close and make good contact when the outhole relay is energized. It is the switch with a blue-red wire and a grey-white wire.

If the 500 point & bonus advance targets do not add bonus during game play, then it is likely to be a dirty/mis-adjusted switch on the score motor. According to the schematic, the switch you need to check is on cam 6 and is the second switch up from the cam rider. This is a make-break switch.

If the switches and the associated wiring mentioned above all look OK, and you never get an add bonus (even during game play), then you might have a wiring problem at the add bonus solenoid of the bonus unit, or an add bonus solenoid coil that is not working.

- TimMe

Hi Twerre
Welcome to PinSide and the joys of an EM!

HP is one of my favorites. I am not a reliable diagnostician by any means but can offer photos/vid if a comparison ever would assist.
The folk who chime in here have aided me immensely.

Pinsider MarkG periodically does an online problem solving workshop which TimMe and other talented folk participate in -- wicked helpful and a blast to just be a lurker : https://pinside.com/pinball/forum/topic/an-em-pinball-online-repair-clinic

So for your second game: a speedy Williams or drop-target Gottlieb?

Cheers

Tom

Glad you got that fixed!

On Bally machines of this era, the bonus issue you are having is sometimes due to a mechanical issue with the bonus unit. This is a pretty easy thing to check. You can test if your stepper is mechanically working OK by stepping it up several steps by hand, and then stepping it back down. To do the stepping, you just push each plunger into its solenoid with your finger, and then release it fairly quickly to see if the gear moves exactly one tooth in the appropriate direction each time. If the stepper mechanism is OK, you'll get good smooth operation in both directions at all times.

If the stepper isn't moving smoothly, it could be something fairly simple - the mechanism may just need cleaning and some minor lubrication. But, if the stepper still doesn't work after you clean and lubricate it, you may have a more serious mechanical issue that is somewhat common with this type of Bally stepper unit.

The bonus unit stepper uses an escapement mechanism to do the downward stepping. Each time the subtract solenoid pulls in the subtract plunger, there is a ratchet that engages a tooth on the plastic gear, at the same time that it releases the main drive pawl from the gear wheel. That is supposed to allow the plastic gear wheel to move toward the zero position about one-half tooth, driven by the tension of the torsion spring trying to unwind on the gear shaft. The torsion spring is under tension from being previously wound up when the stepper was going up (adding bonus).

When the subtract coil shuts off and the subtract plunger returns to its at-rest state, the escapement ratchet is supposed to dis-engage from the gear tooth at the same time that the main pawl re-engages the gear, at the next tooth down. The net effect of this is that the gear should step down exactly one tooth each time the subtract plunger makes one complete operation in and out of the solenoid.

If the action of this escapement gets messed up, then the stepper may not step down each time the subtract plunger operates, or it may skip more than one tooth per subtract plunger operation. This will cause either a bonus over-count or under-count.

Other than cleaning and lubrication, the two main ways this escapement action can get messed up mechanically is due to either the ratchet and pawl parts getting worn, or due to one of the black pivot posts that stick up from the metal base plate coming loose on the baseplate. Both of these issues can be fixed, but are usually non-trivial to deal with.

In any event, it's a good idea to confirm that the mechanical operation of your bonus stepper unit is working properly before you look for an electrical circuit problem with the bonus count.

- TimMe

That's good news, as it is kind of a PITA to fix those Bally stepper mechanical problems.

If the stepper mech is in good shape, your bonus count is probably out of whack due to a fault somewhere in the switching logic. The root cause of those types of issues can be more difficult to find, but they are almost always much easier to fix than a broken stepper, if that helps at all.

- TimMe

For the bumper issue, it sounds like one or more of your "500 points and add bonus" playfield switches is gapped too close. The vibration from the pop bumper is causing a too-closely gapped switch to make contact, and that is giving you the extra score.

- TimMe