Hello all, I am new to this forum.

I have a 1977 Gottlieb Vulcan. I have to manual and schematic. The game has played fine for a couple month, since I got it. All features and scoring worked and everything appears to be original or oem replacements with good work/solder joints.

As of about a week ago, when one of the 9 targets is hit, it scores a double bonus on balls 1-4. On the 5th ball, the 2x light comes on and It scores a double bonus as it should when a target is hit.

I have cleaned contacts in numerous places, relays,and the motor. I don’t understand how/what controls the bonus advance stepper unit. I get 5-pulses from the motor (1A) and then a pulse (2b) to release the bonus relay.

What I don’t understand is how the machine controls the use of those bonus pulses from the motor (1a). Right now the first two advance the bonus unit then nothing for the next three; after which the bonus relay is released by the motor (2b). What tells the bonus stepper to use one or two pulses from the motor instead of all 5, i think I will find the problem when I understand that.

I have familiarity with electronics/electricity. I am a licensed ham and have worked on jukes boxes and other older devices in the past. I am just new to pinball machines and the schematics are a bit of a challenge to read...especially with respect to the motor.

Thank you in advance for any thoughts.

Curriedog, I apologize for my ignorance, but I don’t know what the picture of the schematic shows me. I am sorry to not get it. What are you suggesting I check?

HowardR, with the machine reset for one player on ball one, 6B is the double bonus relay. The switch you identified as normally closed shows continuity between the yellow/red wire and black/whit wire. I did check continuity back to relay K for the red/yellow wire and it is fine. It was also open at K per the schematic, not connecting to the Slate/red wire going back to the bonus unit zero position switch.

I have a typo in my original post, I do have the schematic.

I appreciate this information so far and welcome any other or more thoughts. Has me puzzled still.

Curriedog, I had a minute to check the switch before heading out. It seems that when in the normal state, player one no targets dropped it is per the schematic. However I want to trace the wires a bit as one all targets drop, with the machine off, it closes the open side, but there is still continuity on the side that should have opened. Hope that makes sense.

I have to travel for work, but will look into when I return at the end of the week. Thank you for sharing some info.

Thank you both, I am out of town on business travel right now, but will look into these ideas Thursday night when I get back.

I really appreciate the input!

Hey guys, I am back and will try the ideas this weekend. Work travel and family has kept me tied with a schedule that was more full than I thought it was, sorry for ghosting.