Hello everyone,

can anyone help with a problem on 4 Million BC please?

When the ball is in the tar pit alley, instead of incrementing one step each time the centre mushroom bumper is hit, it exits the alley.
As far as I can tell, this is controlled by the advance ball relay, which is de-energised when motor switch 8D opens, this is working but by the time the cam gets to open the switch the ball has exited the alley. The motor speed seems ok, I can't see how the sequence can happen quickly enough to allow the ball to move only one step.

Any suggestions welcomed, thanks, Richard.

Hello Rolf and Jeff,

thanks for your responses.

My understanding of how it works is that the tar pit gate solenoid is controlled by the tar pit relay (interlock). The gate is open at the start of a game. When a ball enters the tar pit, it hits the top tar pit rollover which causes the tar pit gate solenoid to close the tar pit gate via the tar pit relay.

This ball is then held at the first of three stops and another ball is served. when this ball hits the centre mushroom bumper, this activates a switch on the bumper which energises the advance ball relay, this relay is held in by its own lock in switch, a make/break switch on the tar pit relay and motor switch 8D.

A switch on the advance ball relay energises the advance ball solenoid which lowers the stops, allowing the ball to roll to the next stop.

The problem is, the advance ball relay doesn't drop out until motor switch 8D is opened by one of 2 cams. Looking at the motor timing diagram, the motor completes a cycle in 180 degrees, and the motor needs to turn approx 154 degrees for a cam to open switch 8D and this takes too long, the ball has rolled out of the tar pit alley by the time the switch has opened.

When the ball exits the tar pit alley, it hits the bottom tar pit rollover, which activates the tar pit relay which opens the tar pit gate to allow the procedure to be repeated.

Only one ball can enter the tar pit alley as the gate closes until the ball has left the alley.

I've checked and cleaned the relevant switches but its got me baffled as to how the sequence can happen quickly enough to work correctly.

Many thanks, Richard.

I have studied the video (thanks Jeff) and I think I have figured it out - when the stop drops below the playfield, another part of the same stop pivots up above the playfield to stop the ball temporarily until the 2nd stop comes up.
On my game, part of the stop is missing (one stop is completely missing)
Looking at the Bally parts catalogue, it shows the ball escapement plate assemblies as having two prongs except the last one which only has one prong.

The ball should move through the alley more gradually than I thought.

Massive thanks for all your help - it was driving me mad!

Richard.

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Hello Jeff,

thanks for the video, it is now clear to me how it works. I shall make some replacement parts and hopefully it will be ok.

Hello Rolf,

the 4 Million BC free ball escape assy. looks to be similar to that on Mad World and Capersville except it has 3 stops instead of 4.

The tar pit gate solenoid is unusual (to me) it looks to be a double wound coil similar as you say, to a flipper coil, presumably to allow the gate to stay open without burning out the coil?

I think its a really good game, my machine is not in the best condition but I will do my best with it.

Thanks again for your help, Richard.

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This is the tar pit gate solenoid.

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Hello Rolf,

I had a closer look at the broken parts and the missing pieces have been sawn off! They are not in the cabinet.

This has been done on 2 stops, one stop is missing and the stop at the top end only has (correctly) one prong.

Why someone would cut the pieces off is beyond me, unless they didn't want the ball to step down through the alley.

I've ordered some steel sheet to make the plates, I think the hardest thing will be rivetting/screwing the two pivot pins to each plate and making a groove for the E-clips.

I'll have a look at the parts link you mentioned but I would be surprised if I find the parts, but you never know!

Thanks again, Richard.

Hello Jeff,

that's worth knowing, I saw that adjustment and put it on 100pts and 1000pts but I'll try it with just 1000.

I made the replacement plates for the ball alley today, I punched out the pivot pins from the damaged plate so I can reuse them but I'll have to make 2 pins for the plate that was missing - I need a lathe!

Thanks, Richard.

Success - it works!

Thanks Jeff and Rolf.

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