Is there ever any problem with non-bonus 1000 pt scoring?

You've confirmed that the bonus unit is working properly? You can manually rotate the bonus unit and it rotates smoothly and clicks into each position? And when the ball drains, you can physically see the bonus unit working correctly?

Some items to check:

On Add "Bonus" Unit switch - yellow/red wire and slate/red wire - Is the switch clean and adjusted properly? Any damage to the switch contact?

Z relay coil - Is the coil damaged or shorting out? Does the coil look burnt or overheated? Using a multimeter, you can do an ohms test on the coil.

(Interesting to note that the Z coil is powered by 6 volts on this machine...)

https://flippers.com/coil-resistance.html

A bulb tester would confirm whether or not the Z relay is sticking on its own. You could connect at 6 volt bulb (e.g. a #44 or #47) across the Z relay coil solder lugs and then watch to see if the relay is ever active when the light is off. Or you might unplug the game while the Z relay is on to see if it stays on.

If it stays on without power the relay may be magnetized. Is there a brass washer between the base of the relay coil and the relay frame? And is the coil mounted to the frame with a brass bolt?

/Mark

I have a Bank Shot which I believe is the “sister” machine. My bonus skips two usually. They are two of the three two for one target shots ( credit for two balls for one target).
One thing you can do with the game on and the play field up in the maintenance position manually cycle the bonus stepper thru its paces. I get the games to reset to zero by manually actuating the bonus subtract coil. The actual stepper resets past the zero point by spring action. I then manually actuate the add relay on the bonus stepper one click at a time. The bonus stops on each termination point / rivet and you should get an audible chime.
I improved my bonus performance by adjusting the moving part of the bonus stepper to better align with making good contact at each stopping point. Cleaned the contact rivets and lubricated the rivets with dry silicon. I do not believe it is the Z relay
PM me if you want to discuss.
Good hunting

Your photo shows a copper band around one end of the coil intended to reduce buzzing. There should be a brass washer on the other end, between the coil and the frame, with the brass bolt passing through it. It's intended to keep the coil off the frame and to keep the frame from getting magnetized.

If the coil stays activated once the power is cut the circuit is fine but there is either a mechanical or magnetic reason the armature won't relax. With the power to the coil cut the spring should snap the armature back to its rest position.

If you can't find a mechanical reason for the binding (switch out of alignment, armature binding on its post, etc.) the armature and frame may be magnetized.

As an experiment you can see if putting a piece of paper or two (or tape) between the coil and armature changes anything. If the frame isn't overly magnetized the thickness of the paper can sometimes keep the armature far enough away from coil to let it work properly.

Ultimately you may want to read up on demagnetizing techniques or look for a replacement frame and/or armature.

I've had two machines with coils that tested OK, but after going thru EVERY other possible option I ended up replacing them and it fixed the problem. Maybe yes, maybe no here of course, but even if it doesn't fix it you'd save time on testing.

Your particular style of coil bobbin does not use a brass spacer washer at the back of the bobbin. The back end of your bobbin has a thick plastic covering around the coil core that provides the correct spacing of the coil bobbin in the relay frame. This photo illustrates the difference. The bobbin on the left uses a brass spacing washer. The bobbin the right (the same kind as yours) does not use a brass spacing washer.

coil backing (resized).jpg

As for the sticking Z relay, have you cleaned and dressed the face of the relay armature? It sounds like your Z relay could be sticking mechanically, rather than being magnetized. Here is a related post that describes the issue I'm talking about:

https://pinside.com/pinball/forum/topic/jumping-jack-scoring-relay-sticks-sometimes#post-6014112

- TimMe

That pic in your post #9 shows the brass mounting screw, not the brass washer that MarkG was talking about. The thin brass spacing washer (if your relay had one) would be located between the back of the coil bobbin and the inside of the relay frame. However, as I noted in my post #11, your relay does not use a brass spacing washer, so you won't find one even if you take the relay apart (which you should do, in order to clean the inside face of the armature and the face of the coil core).

- TimMe

I wondered about that myself so I dug a little deeper:
Relay Coil types (resized).jpg
I expected the bobbin type to correlate with the coil number but it appears that that's not the case. Apparently the bobbin type evolved away from the brass washer (left) in favor of the plastic cover (right) over time. The newer type was probably cheaper (to manufacture and to assemble) and more reliable since the washer couldn't be incorrectly installed outside of the frame.

Yeah, the bobbin form-factor is not related to the coil part number. Gottlieb updated the bobbin format a few times over the decades, usually without changing the coil number. The earliest bobbins were cardboard and fiberboard, which were updated to plastic in 1960s. The final version of the bobbin with the thick backing came into use in the early 1970s. The Gottlieb part number of that final bobbin version is D-15341, which you can see molded into the front face of the bobbin.

- TimMe

Hey chip I was wondering if you can help out I need a few photos of the bonus unit on the sure shot the side with the springs on it cheeres.
Raff

Can somebody tell me what the adjustment is on one of the coils on my sure shot bonus unit. The whole coil bracket slides to adjust the throw of the plunger I was just wondering why and what the correct adjustment would be t y i a

From the GTB 1978 parts catalog. Adjustments at bottom.

236ABBF4-9F1A-4A9C-A317-EFD56125EF78 (resized).jpeg

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Thank you. Very helpful.

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