I just picked up a 1961 Williams Add-A-Ball pinball machine from an elderly uncle. I have fond memories of playing it as kid, in the 1970 and 1980s. I don’t think it has been used for about 15 years, and I don’t know why.
I am new to this, so bear with me. I visually inspected the electricals components and wires and the only thing that looked out of place was the lock out relay coil. I plugged it in and nothing came on. I pushed the lock relay and some of the playfield lights came on very dim. I ordered a new coil for the relay and replaced it. Tried it out and got nothing again. The relay does not move. So I tested the transformer, and it read 120 V in, but only 2 V out on any of the terminals, the 6V and the 50V. Am I testing the transformer wrong, or is it no good ?
If is it no good, what are my options ? It is labeled Nelco #6764X1

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Thank you. I tested the 120V input by touching the MM red lead to the top terminal and the MM black lead to the cabinet ground. That does of course read 120V. When I touch the 6V or 50V terminal withe red and the black lead to the cabinet ground, I only get 1.5 to 2V.
Am I testing wrong ?

Mopar, I could use the schematics. Thanks

My latest effort: I used a plastic rod to push the Lock relay closed and nothing. Then I push the lock relay and game over relay closed. The playfield lights came on. I was able to activate the playfield bumpers, flippers, targets and switches on the playfield. The two steppers unit which take in the scoring data were both rotating/indexing. However, nothing in the back box is working, no lights or scoring. I order the schematics to help me understand the machine.
Any trouble shooting advice?
I still can’t get a volt reading at the transformer outputs, but I thought I should include the other symptoms.

That's my issue. I did replace the lock relay coil. Still not activating when I plug in the machine.

Some success tonight !
I noticed the two open switches at the Lock Relay did not appear to contact when I manually moved the armature. So I adjusted them, checked the Kick off and tilt switches. Bingo, it started when I pressed the start button ! But all that happens now is the playfield lights are on and the stepper motor just keeps turning. Nothing turns on at the Backbox or score wheels or the other stepper near the back So I made my first baby step, but not there yet. Thanks for the guidance so far.
Any suggestions what to check next ?

Almost there! The obvious symptom was nothing worked in the Back box. I cleaned the wire harness connector pins and ensured they fit snug into the receivers. However the score wheel reset had an issue. I noticed the “10” score wheel was not moving, so I indexed it to zero.
The machine works, except the “10” score wheel! Researching how to address that issue.

Got it!

Took the "10" score wheel assembly apart. The shaft / bushing was gummed up with old thick grease. Cleaned it now it rotates / ratchets quickly. However, during game reset, it would to not go to zero. The two wires going to a terminal on the zero position switch were disconnected. Soldered them on, now the game works! Just need to replace some light bulbs.