(Topic ID: 212327)

Doctor Who MPF: Height Issue In "Down" Position


By PSUTownie

1 year ago



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  • 3 posts
  • 2 Pinsiders participating
  • Latest reply 1 year ago by PSUTownie
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#1 1 year ago

I am finally getting some time to go-through a Bally Doctor-Who that I dragged home late last year. I picked this game up with the knowledge that the MPF was none functioning, had been previously disassembled, and "may, or may not" have all the parts included. A quick look revealed that the original DC motor, gear box, cam, and mounting bracket were missing in their entirety (the rest was there). I picked up a new box/motor, wiring pigtail, and used bracket/cam and began to piece the assembly back together under the guidance of the online resources, and the extensive forum threads on the topic. The re-assembly went very well overall, and all components appeared to be in good condition with little wear, and no damage. My effort was not without the seemingly-common CW/CCW error issues, which on this example, were traced back to a broken wire at the under playfield motor-directional board.

I now have the MPF functioning as designed; however, in the fully retracted position (down), the MPF parks in a position that is ever-so-slightly higher than the main playfield. Visually, this difference didn't seem like it would be a real issue, but in game play, it creates a rather violent ramp effect and will not allow the ball to even enter the MPF area! The surprising thing to me is that this issue does not seem to be consistent with the other "cant" related issues that seem to be common, and caused by a misalignment of the static MPF framework. On this one, the height differential is fairly even/constant from one edge of the MPF to the other.

Has anyone ran into this before? Any input/suggestions on where to go next are greatly appreciated.

A link to a video of the MPF working through the test sequence is below for reference.

Thanks in advance!

#2 1 year ago

It's very common to have these issues. Yours is not bad. If you put a cliffy on the main PF, it might serve to ramp the ball up to the MPF without doing too much.

I've seen many hacks with washers / removing wood to adjust the height.

At the base of the bracket is an "L" shaped bit of metal. It attaches the motor assembly to the bracket. Was that "L" bracket present or did you fabricate it? If it's original that's a good thing. IIRC adding washers on the bottom of this bracket will push the motor, cam and ultimately the bracket down. It's been a while since I've looked at that action.

Let's start simple. The opto at the bottom of the bracket controls the stopping point. If it's off 1/8" left/right it will impact the center point. Is the opto pair aligned well.

The cam gaps signal it's home. Another hack is to add a small flap on the cam to close the gap. You're just stopping light, so a piece of duct tape would do it to test. I've seen people remove material from the cam and/or affix permanent plastic/metal flaps.

faz

#3 1 year ago

Faz - thank you for your reply. Your suggestions helped to point out an adjustment option that I previously overlooked!

To answer you questions, the L-Bracket on this pin is an original, its just from another DW game. I did make an attempt to adjust the bottom-opto like you suggested; however, I found that on this example, there was not much simple-adjustment to be gained... either way.

I ended up going with the "spacer-method" (between the L-bracket and the MPF track) to lower the whole motor/cam assembly and, by default, the MPF surface. After trying a couple different spacer iterations/thicknesses, it ended up working perfectly!

Thanks again for the game-specific assistance, and for the comprehensive manual you put out on servicing these DW MPF's.

Cheers,
Jon

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