Im new to Pinball restoration but recently acquired a 1968 Williams Doozie Machine. Replaced some burned out coils and cleaned all the switches. However, the lock relay, and the 'Match unit' solenoids continuously buzz (jammed on) when a game is started. When a kick bumper is activated, these solenoids also continuously buzz once activated. I have to turn the machine off before they over heat. Everything else, score board, pop caps, flippers etc seem to work fine.

There is a bridge rectifier that looks like it has been added on more recently. I don't know what this is for but I heard that buzzing coils could be due to receiving the wrong current so don't know if this is the place to look?

I have run out of ideas, would be very grateful if anybody might know what could be the cause?

Thanks for your replies.

It turns out the rectifier was added for some sort of free-play mod so nothing to do with the problem.

I was aware the lock relay is always driven but the buzz is considerably, unavoidably loud that cant be normal. I have disconnected this coil and closed the switches to get around the issue.

The match unit relay buzzes very loudly as soon as a game is started and after the score reel has reset to zero.

The left and right kickers wont stop buzzing after activation.

I thought these 3 issues could all be related and hence a common fix, but will go back to the schematics and try and debug further.

ok thanks this helps. The score reel advances for the pop bumpers (the match unit does not step). The score reel and match unit do not advance when the kicker is activated.

ill go back and check all the contacts on the score reel - many thanks for your help