When you grounded Q15, nothing happened because it was already turned on.

Check SDB J2 pins 1 & 2. They go to the flipper button. Also check SDB J1 pins 8 & 9 to the return side of the coils.

I'd suspect your EOS switches. Misadjusted, or in need of cleaning the contacts. File and adjust them. Ohm them out to verify they are not high resistance across the closed contacts. You would assume the solenoids are wired correctly, but they could be wired wrong too. I've seen that.

If you solder put a blob across the #3 to #5 and the #4 to #6 on the relay pins, the flippers should work any time you turn on the power switch as long as there is no other problems. If this corrects your problem then you need a new relay.

Does Bally have the one amp slo-blo fuse on the lower side of the play field like the classic Sterns? If so, and if that fuse is blown you are dead in the water.

Here is your flipper and outhouse circuit. Does the outhole kicker at A3J1-5 work?

Could the flipper relay in the A3 SDB have gone bad?

Screen Shot 2020-11-30 at 10.51.47 PM (resized).png

Then J-1 or J-2 needs to be repined. Most likely both.

I assumed the outhole kicker was for your ball launcher. So, your outhole kicker works.

The bottom part of the drawing shows a solenoid coil that has not been identified. This might be your Grotto kicker. You would have to check your Grotto coil wires and try to match them to the call out for the unidentified coil.

Screen Shot 2020-11-30 at 11.09.49 PM (resized).png

You say you have voltage to both coils.

Ballys and Sterns have many similarities. but I know Sterns. The coil trigger wires on Stern flippers have an orange wire traveling from the relay to the right hand coil and a green wire that travels form the relay to the left hand coil. I don't know what colors Bally used but the pattern should be the same.

Take your DMM and check continuity from the relay to each flipper. If you have continuity to the flippers from the relay and you have voltage to the flippers then can see little that would be causing your problems except for that relay. And I do not know how to test a relay.

Also, one more thing. On my Sterns, the flipper button switches themselves have a common orange wire. I'm not sure where that wire goes without researching it. I assume Playboy would have a common wire to both flipper buttons, but I would check what board that common wire goes to and check continuity there also.

As usual, a lot of what I come up with is a wild ass guess. But a lot of times I am correct.

My money is on a bad relay on the SDB. The pin has been sitting awhile? Correct? Maybe it was put into storage for a reason no one could figure out.

EDIT: I just saw your post to Grumpy.

There are two sets of winding in the coil. Are you sure the EOS is wired across the higher resistance winding?

Open the EOS switch and measure the resistance across each set of windings in the coil. Make sure the EOS switch was wired across the higher resistance winding. If it is across the low resistance winding, the flipper won't flip.

How about a pic of the cabinet switches. There should be an orange wire going from the switches to the rectifier board J-2 pin 9. This should be ground. Maybe this got disconnected.

Correction: Your Grotto kickback is here. And I now have no idea what the unlabeled coil represents.

Screen Shot 2020-11-30 at 11.38.13 PM (resized).png

Here are the schematics to Playboy. They are rather fuzzy and hard to read but you can expand their size which might help.

https://www.ipdb.org/files/1823/Bally_1978_Playboy_Schematics.pdf

Are you asking how to check the resistance across the windings? If that's the question, then...
there're three lugs on the coil -- A, B and C. Measure all three combinations: A-B, B-C, and A-C. One of these reading will be low resistance. One will be higher. And a third reading will be the sum of the other two. For example, A-B is 3.3 ohms, B-C is 17.2 ohms, and therefore A-C is 20.5 ohms. The EOS switch needs to be wired across the two lugs of the middle resistance reading. In the example, lugs B-C.

All of the other items that have been brought up have been no help as of yet. Coils wired incorrectly could be a real possibility ( remote but real ). It is possible someone worked on this pin years ago, made a mistake and could not correct it. So the pin winds up being buried under trash and forgotten about. And now it's comes back to life---with no history of why it was just sitting.

Looks like the EOS switches are wired correctly. How about the SDB? Hard to tell by the picture, but the soldering on the pins looks suspect. Take a closer look at the soldering, and maybe ohm out the pins/traces for bridging or breaks.

Screen Shot 2020-12-01 at 7.27.50 AM (resized).png

This is a real simple circuit to troubleshoot. the brown wire side of the flipper coil should have 43v DC. The other side gets a ground to fire the flipper. To test, hook up a test wire with one end grounded to the frame and momentarily touch it to the other side of the coil. the coil should fire. If it does good coil.
Once you determine the coil will fire if a ground is delivered then work your way backward in the circuit with the ground test lead and see where shorting to ground does not fire the coil.
The circuit is as follows, ground leaves the rectifier board on the cabinet connector and travels to each flipper button. From the flipper buttons it travels to J2-1&2 on the SD board and passes through the enabled flipper relay. It then leaves the SD board on J1-8&9 and arrives at each flipper coil.
A ground at any point in this circuit will fire the relay if the 43v is present.
Looking at the photo above. there appears to be a cold solder connection on the backside of J1.

Good luck, -Al-

There can only be two things to stop both flippers from working at the same time, the relay which you bypassed with the solder blob. Second is the orange wire going to the rectifier board. On these early Bally games the rectifier boards are usually burnt up real bad. I would take a jumper wire from a known good ground source and connect the other end to the orange wire on one of the cabinet switches, turn on the game and see if the flippers work now ( relay solder blob is still intact).

I agree with what you say. But what about that crappy solder job that Jethro highlighted in post #22? That is some ugly solder work.

Leave the ground jumper on the orange wire and remove the solder blobs from the relay. Retest the flippers, but now you will have to start a game to make them work. This will tell me whether there is more then one issue or not.

Remove the excess solder with this.

https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChcSEwi2xIeRvODtAhXO8MAKHTeiCTsYABAUGgJpbQ&ae=2&ohost=www.google.com&cid=CAASEuRo7l6zxnHrm1pdCjhSMwSh0g&sig=AOD64_3fpwwIVFQi4OEwFOdyPNc7ddymXg&ctype=5&q=&ved=2ahUKEwjvg4KRvODtAhVDVc0KHUkuCkAQwg96BAgBEDg&adurl=