maybe spanish?

open = abrir
closed = cerrado

if so, 7A could mean the switch stack(s) have 7 normally open switches on it.

2A 4C 1CO could means 2 NO, 4 NC and 1 make/break switches. It does not say what position on the stack each switch is ... however, it should be obvious if you manually move the switch armature plate and watch what the blades are doing.

there's a couple pieces of background that will make life easier.
1] can you rotate the score motor cams by hand ... try with the power off turning in the same direction the motor does it
2] how many notches are on the index cam ... can you post a pic of the cams at an angle or take a video of the cams running? You can email the video to [email protected] if you don't have a place to put it and make it accessible.

if you're stuck, I'll be going to the pacific pinball museum warehouse next week and will pull a new world out of the piles and get some info.

in below, Jx means J2, J3 or J4. Tx means T1, T2, T3, or T4.

for adding players, the game works by tripping the Jx relays. When you reset the game, the I relay should power and stay powered until DM, G or F powers (you shoot a ball and score some points). If the score motor runs when I is powered, the next Jx relay should trip and enable the next player.

the balls played unit is keeping track of the balls played AND which player is active. In a 4 player game, the balls played unit steps once every time a ball is sent to the shooter. The next Tx relay is powered, and switches on the Tx relay direct scoring to appropriate player reels, light the player up lights, etc.

You should never see more than one Tx relay powered at the same time. If you do, multiple players will score at the same time. Usually this happens if the wipers on the stepper unit are bridging rivets because the unit is not stepping correctly.

when you have less than a 4 player game, the balls played unit needs to step multiple times to advance over the inactive players. Switches on the untripped Jx and Tx relays make that happen.

ok, so a score motor cycle is 180 degree rotation of the cams. J2-J4 activating in one cycle is wrong, so deal with that first.

below is the schematic for enabling players. J2-J4 are "interlock relays" ... they have two coils each and can be tripped and reset by powering one or the other coil. They stay in that state.
new world player enable (resized).png

1] when you reset the game, the C relay powers and J2-J4 reset coils are powered by an index switch. (green highlight). You now have a 1 player game. The P relay does not power during reset.

2] cycle the game again and the P relay powers and the C relay does not power (not shown on below schem). The circuit completes to the score motor switches 1B, 3B and 5C. The key thing is only one of those switches should be closed at any given time, and they close in numerical order.

3] when 1B closes, the circuit completes to the J3 switch ... but that relay is untripped, so the switch is open and nothing should happen to J4

4] same with 3B ... circuit completes to an open J2 switch and nothing happens to J3

5] when 5C closes, circuit completes to J2 coil and J2 trips. Now all the J2 switches are in the opposite state from what is shown on the schem

6] score motor cams complete 180 rotation and stop ... but note 1B and 3B already did their thing, so although J2 is now tripped, it's too late to affect J3 on this cycle.

when you cycle game again, J3 switch is still open so nothing happens to J4. However, J2 is now closed so 3B causes J3 to trip, enabling player 3. (blue highlight)

cycle again and J4 trips to enable player 4. (yellow highlight)

none of the above cares about what the balls played unit is doing, so figure out why J3 and J4 are tripping on the same cycle as J2 then you can move on to why the balls played unit is not stepping correctly.

new world has a plug in the score motor wiring you can pull out to disconnect the score motor. What I'd do is reset the game, then yank the plug. Push the replay button and verify the P relay is powered, then turn the cams by hand and see when J2-J4 are tripping. If all three trip at the same time as you turn the cams, someone has messed with the wiring.

if J4 trips first, then J3, then J2, the switches on those relays aren't working right. Can you post a pic of J2 in the tripped and untripped state?

if you are playing a 1 player game, then every time the impulse switch stack closes the A switch the "add player unit" solenoid should power and step up the player unit.

at each player unit step, the next Tx relay should power. e.g. T1 is powered on player 1, T2 on player 2, etc.

in addition, Y and maybe Z relays need to be powered until the balls played unit is at the right place.

I don't know what a few switches are doing ... there's a "balls unit" switch that bypasses Z at schem 10C and a bunch of trough switches.

to minimize giving ya a bunch of bs, I'm going to pull a new world out of the piles at the pinball museum warehouse on monday and collect some info on when some switches operate.

if manually rotating the SM cams gives variable results, that's helpful.

you know the first pulse to get from player 1 to player 2 is coming from score motor 2B, so you can ignore any impulse switch movement that happens before (if any). Do this:

1] turn cams past 2B and verify balls played unit stepped once

2] watch impulse cam stack and turn cams enough to make the stack go up/down once. Stop turning if the balls played unit step-up coil didn't power when the impulse stack is lifted almost all the way up or at the latest immediately after it flopped down.

the cams should be sitting at a place where you just missed a step-up pulse, so:

1] verify Y, Z and the appropriate Tx relay are powered

2] lift up the impulse cam switch stack with your finger higher than the cam lobe would do it and see if the balls played unit steps. If no, easy thing is make sure you stop turning the cams when impulse A is closed and then you can poke around in what should be a closed circuit with a voltmeter to see where the 24V disappeared. One meter probe on the red wire on the add balls played unit coil and other probe in the active Tx relay path to that coil.

I don't know how you are adjusting the switches. Just to make sure:

1] you should be adjusting the short blades

2] the switch stack should always be in contact with the cam edge and all the long blades are applying a little down pressure so they follow the cam profile without slop.

3] the switch contacts should change state when the stack travels around 3/4 the distance up a cam lobe. You should see the long blade move the short blade visibly after the contacts touch. Sometimes the movement is very slight, but on cams it should be really obvious. When a cam is opening a switch, you should see the long and short blades both moving a little before the contacts separate.

I never would have bet on 2B. If that one is flaky, you'd have the game staying on the same player instead of advancing to the next one.

I think the other guys problem is different. His 2B always works, but the other circuits that advance over non-enabled players don't work reliably.

I don't think I was clear in previous stuff wrt 2B.

it needs to close at the same time as impulse A is closed, so your comment about impulse A not being closed long enough can affect the 2B circuit.

since the impulse cam pulses the A switch a few times during the score motor cycle, 2B's job is to let only one pulse thru to step the balls played unit. The other parallel circuits around the 2B switch let an additional pulse thru for each non-enabled player.

anyway, sounds like ya got it sorted. If it gets flaky again, check the relationship between 2B and impulse A.

general comment first.

the switch stacks should stay on the cam edge always. If the stack is floating a little above the cam, it won't be reliable. When a notch rolls around, the stack needs to snap down into it.

you have to adjust the tension on the long blades to apply down pressure, then you may need to adjust some short blades so the contacts work right.

pedantically, it's the plastic cam follower that is sitting on the cam edge, but the red lifter piece needs to stay down on the follower blade always.

trough switch tmi
--------------------

you have a single switch where the ball lands as it leaves the playfield. Most manufacturers called that the outhole switch (I'll call it that below to avoid more confusion). It has RD-GR and SL-WH wires on it and it powers the U relay. That causes the bonus to count down. How many score motor cycles (180 degree rotations) depends on the amount of bonus, so it can be different each ball.

when the bonus unit reaches reset ("0" position), the Y relay is powered, but not the Z relay.

because the Y powered, the ball is kicked over to the shooter and U loses power. On the way the ball passes over the rollover activating the other trough switch stack, which closes two switches at the same time.

one switch with SL-WH and BLK-RED wires powers the Z relay, and unless V is powered for an extra ball (shoot again), Y and Z will both be held powered until score motor 6C opens.

the other trough switch with the MAR and SL-WH wires steps up the bonus unit once so the position '0' switches change state

because the Y relay is powered, the score motor is powered.

yeah yeah, but what about the problem
--------------------------------------------

impulse cam A switch with WH and BLK-MA wires is sending pulses into the circuit that steps the balls unit coil. When Y and Z are powered, those pulses can reach the step-up coil.

2B and imp A switch close at the same time and steps the add balls played unit. The player advances to the next one ... whether it's enabled or not. That always happens.

now the circuits around 17E come into play. They power one of the T1-T4 relays. e.g. If you are on player 1, T1 is powered.

look on the schem around 10E. If 2B moved you to player 2, then T2 is powered. If J2 isn't tripped (player 2 not enabled), then the next imp A pulse will pass thru and step the balls played unit again. Repeat for T3/J3 and T4/J4 and you are back to player 1.

the stepping of the balls played unit 4 times to get back to player one should happen in 1 cycle - 180 degrees of cam rotation. It actually has to happen before 6C opens, which is why the impulse cam lobes are bunched together. Note the first lobe happens before 2B is closed, so it's not used for ball unit advance.

if the ball unit it doesn't step every time the imp A cam switch closes (after the first time), there's some possibilities:

1] the player it stopped on has an issue with the Tx/Jx switches or the wipers on the player unit aren't powering Tx.
2] the imp A switch is flaky and not making reliable pulses
3] if Y/Z are unpowering too soon, 6C is not reliably closed
4] the Y or Z switch in the circuit to the add balls played coil are flaky

enough already!
------------------

do your disconnect the score motor and spin by hand thing. If you want to test with bonus and have the playfield tipped up, you need to hold the outhole switch closed (or jumper it) while you spin the cams until the ball return coil fires, then you briefly need to close the other two trough switches to get Y and Z to power and step up the bonus unit. If you jumpered the outhole switch, remove the jumper before closing the trough switches.

if you want to cheat a little, you can manually reset the bonus unit and close the outhole switch with your finger. The ball return coil should immediately fire and you can let go without turning the score motor cams. Then operate the trough switch stack and start spinning the cams by hand.

as you rotate the cams, the add player unit should power every time the impulse cam stack goes up. If it doesn't, leave the cams with the impulse stack lifted and see if Y and Z are still powered. Then I'd just use a voltmeter with one probe on the RD wire on any handy coil and the other poke in the add balls played coil circuit to see where the voltage dropped way below 33VAC.

also note that when a pulse doesn't make it to the add balls played unit due to a flaky switch, the next one might if Y and Z are still powered. However, when 6C opens, Y and Z will unpower and you are left on whatever player you are on. The score motor will not do another cycle unless you cheat and close Z again via the trough rollover or push the armature onto the coil top with your finger.

also, when adjusting the trough switches, use a ball on the rollover wire to operate the switches. Don't use your finger, as it can push the rollover down further than the ball can.

the long blade tension is what pushes the rollover wire up. You want those blades to push the rollover just enough to be all the way up, but not much extra tension or you could slow down/stall the ball on the way to the shooter.

if you got this far, get a beverage.

the sequencing starts when a trigger happens ... in this case, the trigger is the ball landing in the outhole.

after that, sequencing is done by the score motor switches or physical stuff like the ball moving from the outhole to the shooter.

you have it relatively easy because most of your score motor switch stacks just activate in order and not at the same time. The thing you have to look at that the schem doesn't show is the impulse cam switches and when they change in relation to stacks on cams 1-6.

I cheated and took a video of manually rotating the new world cams at the museum warehouse ... that's how I saw the first impulse cam stack activation happened before 2B so it's not relevant to the circuit operation.

anyway, keep in mind the two main principles:

1] score motor 2B ALWAYS advances to the next player, whether that player is enabled or not
2] if that player is not enabled, then the Jx + Tx switches should cause the add balls played coil to fire more times to keep advancing the player.

logically, if you are playing a 1 player game and the player advance goes to player 2 and stops AND the Y and Z relay switches are closed, then T2 + J2 is not working.

if you get the score motor to cycle again, 2B will move the balls played unit to player 3, and now T3+J4 and T4+J4 work and get you back to player 1.

if something in the T2 + J2 path is intermittent, then it's possible for one of the impulses to get through and move the player. However, there's only four impulses, so if more than one is needed to get the player to move from 2->3, then you'll run out of pulses before getting back to player 1 even if the T3 and T4 circuits are working fine.

that's how you can wind up on player 4 sometimes ... one of the previous steps needed more than one pulse to advance the player.

so here's what ya do:

1] do the manual cam turning until the add balls player unit steps the player to player 2

2] keep turning the cams until the impulse cam switch stack is lifted. At this point, the add balls played unit coil should power. Assuming it doesn't, stop turning the cams with the stack lifted.

3] verify that T2 relay is powered

4] put a voltmeter probe on the red wire on the add balls played unit coil or any coil with the red wire. It daisy chains to most of the coils. (red line on below)

5] put the other probe on the BLK-MA wire on the J2 switch (green dot). You should see around 33VAC. If you don't, the impulse A switch isn't closed. Try lifting the impulse stack with your finger.

6] if you do see the ~33V, move the probe from the green dot to any of the blue ones. If you see the 33V drop way down, something is wrong between the green dot and where your probe is.

note that if a solenoid does power (solenoid = coil + plunger), don't leave it powered for long. Solenoids are high power and will burn up if left powered for too long.

tmi as usual
--------------
the ideal way to use a voltmeter is to probe in a "closed" circuit. When the circuit is closed, current is flowing and you should not see any significant drops in voltage along the circuit path.

I dunno if it will help, but there's a confusing writeup here: http://bingo.cdyn.com/techno/readschem/

the key takeaway is:

1] do what you need to do the have a closed circuit path so current is flowing. Jumper wires are a valid shortcut if you don't want to fiddle with positioning units or the score motor cams.

2] put one meter probe on the common power wire for the load (where load = coil, lamp, motor) and use the other probe to poke around in the circuit that is feeding the other side of the load.

you should see the full transformer voltage if you stick the probe on both sides of the load - e.g. both coil lugs. If you don't, leave a probe on the common wire since that's often tied to the transformer - and if it had an issue lotsa stuff wouldn't work - then move the other probe to places along what should be the closed path and see where the voltage is back to the transformer output. When it goes to transformer voltage, the circuit from that point back to the transformer is good and your problem is between the probe and the load.

e.g if you poke one blade on a closed switch and see 33V, and poke the other blade and see 23V, the switch is dirty, not closed well enough or you have a bad solder joint.

another option is just use a jumper wire. The white wire on the transformer is common to the 28, 30 and 33V circuits. If you clip one end of the jumper there and poke the other end into the circuit at the green/blue dot points, the coil should power. If it doesn't, the circuit has an issue between where you jumpered to and the load.

the only issue with using a jumper is if the coil does power, you may need to set up the circuit again. The voltmeter won't do anything unless you short something with the probe tip or the pressure of the probe fixed a poor connection briefly.

new world vm (resized).jpg

you definitely don't want the cam switches with really tiny switch gaps.

the impulse cam lobes are pretty close together. If the switch gap is small, then the switch may not open long enough for the coil to lose power and step the unit before the next lobe closes the switch and powers the coil again.

in effect, 2B would power the coil and it'd stay powered until all the impulse cam lobes passed under the stack.

more generally, what you care about with switches is "overtravel". After the contact on the moving blade touches the contact on the mating blade, you should see the mating blade deflect a little. Manufacturers would quote numbers like 3/32" of deflection.

in practice on something like a cam operated switch:

1] if the switch is normally open, then it should close when the stack changes position around 3/4 of the way. The other 1/4 provides the overtravel.
2] if the switch is normally closed, it should open when the stack is around 1/4 into a position change. Again, the 1/4 is the overtravel.

position change = stack lifted by a cam lobe or stack dropped into a cam notch.

don't worry about being exactly 1/4, but do worry about the overtravel. e.g. if your NO switch changes when the stack is 1/2 to 7/8 changed, that'll almost always work fine too.

the easy thing is rotate the cams by hand with the power off and watch the switches. The long blade should cause the small overtravel, not bend the short blade a lot (most of the stack position change) because the contacts touched too soon.

the other general gotcha is make-break switches - the kind with three blades with the long/moving one between two others. Technically the moving blade should disconnect from one contact before connecting to the other - unless the switch is specifically labelled as "make before break".

if a make-break behaves like a make-before-break, it usually doesn't matter ... but occasionally you get bitten. e.g. the bonus scoring on a solar city.

the worn cam follower (white plastic piece) will reduce the stack travel and slightly change the timing, but it should still work ok.

your post 33 sounds like correct behavior when only 2B is working.

lemme try another description, assuming you are turning the cams by hand

1] you are playing a 1 player game, so J2, J3 and J4 are not tripped.

2] ball 1 drains and 2B + impulse steps the add balls unit to player 2 once any bonus is counted off. That is correct. The impulse A switch should be between cam lobes after the unit stepped, so stop turning the cams.

3] look at the Y, Z and T2 relays. They should all be powered.

4] slowly turn the cams until the impulse stack is lifted and stop with the cams lifted if the add balls unit coil didn't power. You can also cheat and just lift the impulse cam switch with your finger instead of turning the cams.

if the add balls unit coil didn't power, you are pooched. If Y, Z and T2 are powered, the only thing left is a J2 switch and a T2 switch. The J2 switch is closed when J2 is not tripped, the T2 switch is closed when T2 is powered.

what is happening?

because your problem is the J2 and/or T2 switches. The second time thru 2B steps the add balls coil instead, then the T3/J3 and T4/J4 circuit paths work.

does the schem in post 28 make sense or do you want a description?

I wouldn't put a lot of faith in the chart on the schem wrt how many of each switch type there is. It's pretty common for stuff like that to be wrong as they often started with schem from an earlier game or a verion with different number of players and made changes, but weren't too good at making all the changes they should.

almost always the circuits are right, it's the extra info like the charts they got wrong.

your J4 relay has six switches, and I found 6 on the schem, so the chart is either wrong or there's something about it I don't understand.

how the switches are drawn on the schem is always a little fuzzy i.e. when is "normally". The gottlieb convention is the game is reset then turned off, but there's still some ambiguity on trip relays and the occasional circuit where the guy drawing the schem didn't bother with the convention.

I just go with what makes sense. In this case, for the balls unit to do what it needs to do, the J2 switch needs to be closed when player 2 is not enabled, so the Jx switches must be drawn in the relay untripped state.

you have the right idea wrt looking at the switches and seeing how they operate. You should be manually tripping/resetting the Jx relays and looking to see if the short blades get moved by the long blades when the contacts touch. Even then, it's possible the switch doesn't work right and you need to use a meter or jumper wire to verify.

those wire colors are somewhat suboptimal

one of the NC switches on J2 when the relay is untripped has yellow-blue and black-maroon wires. If you aren't comfortable poking around with a voltmeter, jumper the switch closed. Yeah, it supposed to be closed anyway, but that's a quick way to see if the contacts have an issue.

you could also jumper the NO T2 switch closed. Then the add balls unit will step on every impulse A closure. You'll wind up on the wrong player, but it'll tell you if the T2 switch isn't closing properly when T2 is powered.

since you can turn the cams by hand, you have the ideal situation for a jumper. Turn the cams until T2 powers and Y/Z are powered and leave them there, then lift up the impulse switch stack with your finger to close the A switch. If the add balls coil didn't power, jumper the J2 switch and lift again. Still didn't power, jumper T2 and lift again. Still no good, jumper both and try again.

if still no good, jumper Y and/or Z switches, but it really shouldn't be those. If still no good, now you must use a voltmeter to see what is going on.

usually you clip the alligator jaws on the switch where the wire is attached. If you can't get to that, it's ok to clamp onto the blade itself.

you can even clamp both blades together around the contacts if you can do it without shorting to something else, but the ideal thing is on the wire solder point since a poor solder connection could be the problem and being on the wires would bypass that.

below is a pic of jumpers attached on a gottlieb game. In this pic, they are connecting a meter, but it shows how you usually connect the jumpers to blades.

PXL_20211108_200116369 (resized).jpg

when the cam 2 switch stack is down in the notch, the 2B switch is closed. You need to rotate the cams until the cam 2 stack is out of the notch otherwise you will stick the BPU coil on ... and you don't want to do that for long. It's the switch stack climbing out of the notch that opens 2B and removes power to the coil.

cams 3-5 don't matter. Those switch stacks are going down/up, but it's the impulse cam stack that is going up/down that is making the pulse to the BPU coil.

normally a stepper unit moves the wipers when the solenoid loses power. Powering the solenoid coil pulls the pawl onto the next ratchet tooth, and when the power drops spring(s) pull the pawl and rotate the ratchet/wipers.

if you turn the cams until the BPU coil powers and stop turning, nothing really happens. You have to keep turning until the BPU coil loses power, then the wipers move and the T2 relay powers.

the Tx relays stay powered the entire time a player is selected. Switches on the Tx relays direct the scoring events to the right set of reels and does stuff like lighting the active player.

so ....

when cam 2 switch stack raises and the BPU coil loses power, stop rotating.

now what happens if you lift up the impulse A switch stack with your finger?

one key point is just because a switch looks closed doesn't mean it works. If the switch has significant resistance between the contacts due to crud, barely touching contacts, pitted contacts, contacts loose in the blade, poor wire solder connection or if the lug the wire is attached to is sandwiched onto the blade with the contact and the interface is loose or cruddy, the switch resistance can lower the current in the circuit enough for the coil to not work.

the purpose of the jumper is to bypass all that stuff connecting the blade wires together directly. When a jumper makes it work, then you get to figure out why the switch doesn't work. Usually people just clean the contacts, adjust the switch travel, make sure the stack screws are snug and look at the contact faces for deep pits/burns.

if none of that works, resoldering the wires is next.

the "sandwich" thing mentioned above is sometimes factory, but it can also be someone in the past did a quick fix for a broken blade or bad contact - or they didn't have a blade with the lug pointing in the right direction ... so they kept the original blade piece with the lug and holes and stuck the replacement blade with no lug next to it. Usually works fine, and you don't need to solder anything.

it's not cam 3 and 4, it's the impulse cam switch. There's multiple lobes on the impulse cam, and each lobe more-or-less lines up with a cam notch on cams 3-5.

the difference the second time thru is the BPU is starting at a player 2 position and 2B is moving the BPU to the player 3 position ... T2 and J2 don't matter anymore.

remember 2B ALWAYS moves the BPU to the next player whether that player is enabled or not. The job of the Tx/Jx relays in that circuit is to keep stepping the BPU when it's on player positions you didn't enable to get back to player 1.

the problem is what happened on the previous cycle ... as soon as T2 powered, the next impulse switch pulse should have caused the BPU to step to player 3. That didn't happen, so the most likely thing is the J2, T2 or both switches don't work right - even if they look like they do.

what do ya do if you can't tell the wire colors
--------------------------------------------------

1] swear

2] get a beverage

3] get your ohmeter and the schematic

4] mumble repeatedly - "must isolate"

isolate meaning you want to try and have only one possible circuit path between the two ends of a wire segment you care about.

in the case, if you can't tell which NC switch on J2 has the YE-BL and BLK-MA wires, do this:

1] stick paper between all the NC switch contacts on the J2 relay.

2] pick a wire that may be YE-BL and dig a meter probe into the solder where the wire connects.

3] poke all the NO switch blades on the T2 relay looking at your meter for almost zero ohms. If you see something that is a few ohms+, that's probably not the wire, but a roundabout circuit path thru other devices.

when you think you found the YE-BL, does the wire on the mating blade look like it could be BLK-MA? If yes, assume you found the switch and proceed to jumper it. If not sure, you can look on the schem where the BLK-MA wire goes and try to prove it's that wire. Since BLK-MA goes to a lot of places, you'd probably need to punt isolation and just look for almost zero ohms on a place you are pretty sure about - like impulse A switch.

impulse A means the bottom switch on the impulse cams. That still leaves you with 2 wires on 2 blades, but one is BLK-MA and one is WH, so hopefully you can tell the difference. If not, try them both looking for almost zero ohms.

the logical thing when a 2+ player game works fine is the T2/J2 path in the post 28 schem doesn't work. That circuit path is only used in a 1-player game.

find/jumper the J2 switch closed and play a 1 player game normally ... yeah, that switch is supposed to already be closed and may look ok, but that doesn't mean it works.

if that doesn't fix the issue, then score motor disabled turn the cams until impulse A is closed when T2, Y and Z are powered. If BPU doesn't power, jumper the T2 switch (which also should be closed)

kinda obvious, but if the BPU powers when a jumper is on the blades of a closed switch but it doesn't work without the jumper, something is wrong with the switch:

1] dirty/burnt/pitted contacts or misadjusted switch
2] cold solder joint at wires
3] if the lug the wire is attached to is not part of the blade with the contact, the interface between the lug and blade can be bad. You have to take the stack apart to fix that if the problem is not loose stack screws

white-blue?

is that the yellow-blue wire between a T2 and J2 relay switch that's faded to white-looking?

'course, that would mean T2 would need to be on the playfield or in the head since J2 is on the bottom board. If I would have looked at the ipdb pics better, I'd have seen T2 was in the head ...

since the plug connections aren't drawn on the schem, you have to know where all the pieces are in the game or hope someone has provided high res pictures so the labels are readable.

intermittent problems are not so fun to find. If the game is screwing up on a particular ball, then suspect the wiper <-> rivet contact on the ball count unit at the problem ball positions. In reality tho, you just take the wipers off and clean all the rivets so they are shiny and unless rivets are damaged, you assume that eliminates the wipers as a source of the issue.

on the post 28 schematic:
- the T2/J2 circuit path is not used when playing 2+ players.
- AND the T3/J3 circuit path is not used when playing 3+ players.
- AND T4/J4 is not used when playing 4 players.

in 4 player, only the 2B path is used, so if there's issues on the Tx/Jx switches or the ball count wipers, you won't see them in a 4 player game.

if the problem only happens in a 1 player game, then it could be T2/J2, T3/J3 or T4/J4 is flaky or the BCU wiper control of T2-T4

if the problem happens in a 2 player game, could be T3/J3 or T4/J4 or the BCU control wiper of T3-T4

if the problem happens in a 3 player game, could be T4/J4 or the BCU wiper control of T4

and, of course, the plug connections between Jx and Tx