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 ....
Quoted from Nikrox2:player 2 is activated from the BPU after Cam 2 (2B) is closed with Impulse A closed - if I leave it in this position the BPU will stay fired so I rotate and Cam 2 raises Cam 3 falls - BPU de-powers
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.
Quoted from Nikrox2:If I activate Z&Y relays again (thru 2nd trough) - all happens as above except - on Cam 3 & Cam 4 the BPU fires as it should. (Is that because T2 was already activated?)
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
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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.