(Topic ID: 253761)

Doctor Who MPF - "Play" in the Main Bracket Assembly


By nhislop

4 months ago



Topic Stats

  • 16 posts
  • 7 Pinsiders participating
  • Latest reply 85 days ago by nhislop
  • Topic is favorited by 1 Pinsider

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#1 4 months ago

Swapping out the main bracket assembly of my Doctor Who (managed to get a replacement via Pinside - woohoo!), the issue is that when I run through the MPF self-tests, when the playfield is in the middle position (specifically, after executing "CCW MID L") it settles in a position where it is slightly too low, the upshot being that when the ball is aimed at the opto targets it is impeded by the lip of the MPF, so doesn't strike the switches / register the hit.

I notice that if I lift the MPF by hand from that position, there is a little play in the mechanism; if I pull it up as far as it will go then the optos are in the correct place.

So, why is there play in the mechanism?

Here is a video that shows you what I am dealing with:

It looks to me as if the set screws joining the cam to the motor are tight; I would have thought that if that was the case then nothing could rotate, and in fact to my untrained eye it looks as if the "D" shape is not rotating, but that doesn't seem right, as the cam seems to do so a little bit.

I swapped out the motor a few years ago, FWIW.

Any help appreciated!

Does anyone have any tips / tricks?

#2 4 months ago
Quoted from nhislop:

Swapping out the main bracket assembly of my Doctor Who (managed to get a replacement via Pinside - woohoo!), the issue is that when I run through the MPF self-tests, when the playfield is in the middle position (specifically, after executing "CCW MID L") it settles in a position where it is slightly too low, the upshot being that when the ball is aimed at the opto targets it is impeded by the lip of the MPF, so doesn't strike the switches / register the hit.
I notice that if I lift the MPF by hand from that position, there is a little play in the mechanism; if I pull it up as far as it will go then the optos are in the correct place.
So, why is there play in the mechanism?
Here is a video that shows you what I am dealing with:

It looks to me as if the set screws joining the cam to the motor are tight; I would have thought that if that was the case then nothing could rotate, and in fact to my untrained eye it looks as if the "D" shape is not rotating, but that doesn't seem right, as the cam seems to do so a little bit.
I swapped out the motor a few years ago, FWIW.
Any help appreciated!
Does anyone have any tips / tricks?

Ok first of all - I would completely disassemble the bracket so you can clean it up. The grease they used way back in the day turns into a hard clay and will definitely
Impede movement.

After that, the bracket that goes across the back is what can be adjusted. But you should also use a T- or L-Square to check that the bracket hasn’t bent. When the rear brace goes out of alignment, the whole thing gets bent. You may need to gently re-align it. Then tighten that rear bracket.

Now before you do any of this go read the best guide about the doctor who MPF: Faz’s guide. It’s in the official DW thread

#3 4 months ago
Quoted from Rdoyle1978:

Ok first of all - I would completely disassemble the bracket so you can clean it up. The grease they used way back in the day turns into a hard clay and will definitely
Impede movement.
After that, the bracket that goes across the back is what can be adjusted. But you should also use a T- or L-Square to check that the bracket hasn’t bent. When the rear brace goes out of alignment, the whole thing gets bent. You may need to gently re-align it. Then tighten that rear bracket.
Now before you do any of this go read the best guide about the doctor who MPF: Faz’s guide. It’s in the official DW thread

All of the above, and that play looks about normal for the game. That whole mech is a royal pain in the ass. I've spent a ton of time on mine and a friends to get the movement as close to perfect as you can with the original stuff, and I honestly have come to loathe the game because of it.

#4 4 months ago

I shimmed my up with washers under the mounting plates, to get it to line up.

#5 4 months ago

Thanks to all who replied so far.

Quickly:

- I am certainly familiar with Faz's MPF guide, as I have taken the wretched thing out my game dozens of times over the last few years!

- It's not sparkling clean, for sure, but you should have seen it before I have cleaned off a ton of the old lube, I will certainly do so again once I have the "play" out of it

- Based on research in various Pinside forums I tried using washers, trouble is that the MPF actually fits really well in all other positions, if I try shimming it then it raises the lip in the fully down position -> no good

- I think I understand where you are going with straightening the assembly, but I am not sure how that would help my issue? It's not that the MPF isn't aligned straight, or that it doesn't sit flush, its that gravity seems to be causing the cam to slip slightly.

I am thinking that this might be a motor / gearbox issue, but before I go there, if you all have your MPF in the center position, and pull on it to lift it up, does it move? Or does the tight coupling of the MPF->Cam->Motor shaft prevent that?

#6 4 months ago
Quoted from dsuperbee:

All of the above, and that play looks about normal for the game. That whole mech is a royal pain in the ass. I've spent a ton of time on mine and a friends to get the movement as close to perfect as you can with the original stuff, and I honestly have come to loathe the game because of it.

Upvoted, except for loathing the game Buy Ulf's kit, you'll never mess with the MPF again.

#7 4 months ago
Quoted from nhislop:

Thanks to all who replied so far.
Quickly:
- I am certainly familiar with Faz's MPF guide, as I have taken the wretched thing out my game dozens of times over the last few years!
- It's not sparkling clean, for sure, but you should have seen it before I have cleaned off a ton of the old lube, I will certainly do so again once I have the "play" out of it
- Based on research in various Pinside forums I tried using washers, trouble is that the MPF actually fits really well in all other positions, if I try shimming it then it raises the lip in the fully down position -> no good
- I think I understand where you are going with straightening the assembly, but I am not sure how that would help my issue? It's not that the MPF isn't aligned straight, or that it doesn't sit flush, its that gravity seems to be causing the cam to slip slightly.
I am thinking that this might be a motor / gearbox issue, but before I go there, if you all have your MPF in the center position, and pull on it to lift it up, does it move? Or does the tight coupling of the MPF->Cam->Motor shaft prevent that?

to confirm if it's square:
Take the MPF out and hook the motor up to a 9V battery. If the bracket is properly aligned, even 9V will be enough to power the motor and move the MPF up and down (pretty quickly too). If it's not aligned square, it will shudder and not go up and down at a consistent speed.

Unless your main playfield is somehow warped, or the bracket tangs (where you screw it into the playfield) are messed up, then the issue is related to the mini playfield. Do you have any washers or other non-standard parts in the assembly of the miniplayfield? Sometimes operators would add washers where they dont' belong in order to shim up the Time Expander, and they would eventually warp the assembly. Make sure everything's all squared up in that respect too.

finally, the test you did in the video there doesn't clearly indicate what the issue is. I'm betting the legs of the actual bracket need to be pushed together just a tiny bit (or maybe one side does). there'slike 1/16" play on both sides, under normal circumstances. If you've lubed it up with silicon lube (and entirely removed the black grease - this is really really important) then the turn of the cam should move it pretty easily. Try the 9v battery thing and let's see how it moves. Put the whole assembly together and set it down. You'll need to prop it up a bit on some books or something so it doesn't put pressure on the motor, but other than that it will balance on its own.

#8 4 months ago

I've been Exactly where you are now.

Its binding and the gearbox is worn.

If there is no binding, both sides raise with very little rocking.

It has to be extremely square from all axis, and completely clean with syl-glide added for lubrication.

It took me several hours to understand the many ways it can bind slightly.

It will always work, but it will be rocky.

No washers needed to fix it.
Just take time to square it up from all directions.

If its low add square shims or even strips of vellum (it doesn't compress)
Washers sink into the wood real fast.

I replaced the motor/gearbox assembly, then proceeded to work out the binding.

#9 4 months ago
Quoted from nhislop:

MPF in the center position, and pull on it to lift it up, does it move?

Is shouldn't move at all.
If it does, your gears are slipping.

In fact, avoid manually moving it to protect the gearbox. Says so in the instructions and manual somewhere.

#10 4 months ago
Quoted from nhislop:

Swapping out the main bracket assembly of my Doctor Who (managed to get a replacement via Pinside - woohoo!), the issue is that when I run through the MPF self-tests, when the playfield is in the middle position (specifically, after executing "CCW MID L") it settles in a position where it is slightly too low, the upshot being that when the ball is aimed at the opto targets it is impeded by the lip of the MPF, so doesn't strike the switches / register the hit.
I notice that if I lift the MPF by hand from that position, there is a little play in the mechanism; if I pull it up as far as it will go then the optos are in the correct place.
So, why is there play in the mechanism?
Here is a video that shows you what I am dealing with:

It looks to me as if the set screws joining the cam to the motor are tight; I would have thought that if that was the case then nothing could rotate, and in fact to my untrained eye it looks as if the "D" shape is not rotating, but that doesn't seem right, as the cam seems to do so a little bit.
I swapped out the motor a few years ago, FWIW.
Any help appreciated!
Does anyone have any tips / tricks?

You can't verify what is wrong in your video because you have too much "slop" due to it not being secure to a rigid surface. I created a rig to attach the assembly, then squared it. Only way to troubleshoot issues.

#11 4 months ago
Quoted from eyeamred2u:

You can't verify what is wrong in your video because you have too much "slop" due to it not being secure to a rigid surface. I created a rig to attach the assembly, then squared it. Only way to troubleshoot issues.

Yep. No way to get an accurate simulation unless its bolted down.

Hopefully exactly the same as the MPF.

#12 4 months ago
Quoted from eyeamred2u:

You can't verify what is wrong in your video because you have too much "slop" due to it not being secure to a rigid surface. I created a rig to attach the assembly, then squared it. Only way to troubleshoot issues.

If the whole mini PF is attached there is enough weight to keep things rigid - but I’m seeing just the bracket in the video. Not a comparable simulation

#13 4 months ago
Quoted from Rdoyle1978:

Upvoted, except for loathing the game Buy Ulf's kit, you'll never mess with the MPF again.

Mines for sale locally

#14 4 months ago

Hey, I've seen a few dozen of these things. That's not bad at all. The action you are recreating however is un-natural. The game never pulls the bracket up, the cam pushes the bracket up. That's a difference.

Above suggestions are good. Squaring the bracket is a must and washers are very common. Slotting the screws in the game to allow for extra gap for the front of the MPF is also a common play.

Follow the canting procedure to help eliminate slop/square up the brackets. A cleanup of everything is certainly in order. It rally won't impact the motion that much but it will make you feel so much better when you resolve these issues

I really prefer getting the action of the brackets outside the game. Place the bottom bracket in a vice (gently) or something to hold it firm and drive it up with a DC power source. 9V-20V will all work fine...I'm sure you have some DC wall-warts out there. Alight the cam such that it's dead center of the brackets (see my guide for the illustrations) and adjust the play with the cant procedure. THEN drop in the game. Adjusting the height comes after that. Oh, pay attention to the angle of the bent tabs at the top of each of the bracket. I was just helping a Pinsider offline with his game and the tabs had a weird twist (he caught that one not me) and when he straightened out the twist the MPF sat dead flat.

Best of luck (and a lot of patience),
faz

#15 4 months ago
Quoted from pinball_faz:

Hey, I've seen a few dozen of these things. That's not bad at all. The action you are recreating however is un-natural. The game never pulls the bracket up, the cam pushes the bracket up. That's a difference.
Above suggestions are good. Squaring the bracket is a must and washers are very common. Slotting the screws in the game to allow for extra gap for the front of the MPF is also a common play.
Follow the canting procedure to help eliminate slop/square up the brackets. A cleanup of everything is certainly in order. It rally won't impact the motion that much but it will make you feel so much better when you resolve these issues
I really prefer getting the action of the brackets outside the game. Place the bottom bracket in a vice (gently) or something to hold it firm and drive it up with a DC power source. 9V-20V will all work fine...I'm sure you have some DC wall-warts out there. Alight the cam such that it's dead center of the brackets (see my guide for the illustrations) and adjust the play with the cant procedure. THEN drop in the game. Adjusting the height comes after that. Oh, pay attention to the angle of the bent tabs at the top of each of the bracket. I was just helping a Pinsider offline with his game and the tabs had a weird twist (he caught that one not me) and when he straightened out the twist the MPF sat dead flat.
Best of luck (and a lot of patience),
faz

Ah yes.
I replaced my bracket with a new one too.

A bit of filing, a lot of twisting in a vice.

The tabs were way off.

The bracket was off square in 6 directions.

It really wasn't made well at all but, after 6 hours of work it ran super smooth.

In fact when I had it running petfectly. I still adjusted it better.

Now it runs like brand new (Cuz it is...lol).

1 month later
#16 85 days ago

Thanks to all for their input, and apologies for the delay in responding - partly because it took time to actually fix the issue, and partly because of work related stuff, anyway...

Like all good pinball stories, there was the fixing of the symptom with many twists and turns, and finally addressing the root cause:

Turns out that the "play" in the mechanism was nothing to do with the frame, or the motor, it was that although the set screws seemed to be tightening against the cam shaft, if fact they weren't. Swapping back the old cam / set screws and mounting in the newer frame did the trick nicely.

BUT - the original issue (that when the MPF was raising to its middle position the ball could not strike the opto targets) still persisted.

Way too late in the process I remembered that this issue first manifested itself after I had installed a Cliffy protector to cover the lip of the MPF. I unisntalled the protector, in the process I imagine that it freed up a few precious millimetres of headroom and - voila! - the ball could strike the targets at will.

In addition, the mechanism just seemed to raise and lower more smoothly.

I am certain that if I scour Pinside I will find other advice about somehow trimming the game to get the Cliffys to function correctly, but as some of you may also attest - life's too short to spend another week or two futzing around with that %&^%$ MPF!

Again, thanks to all for their advice.

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