At the end of the "Dr Who Mini Playfield Electrical Issue" thread, I mentioned that the MPF was working near perfect, but seemed low on the left at the Down position, and also was too low after descending to Mid Level. I thought I better move that issue to a thread with an appropriate title.

I pulled the MPF and performed procedure to correct canting. I wasn't able to correct the problem, though the MPF in the down position seems to be a bit more toward flush on the left side by maybe 1mm. If I grab the left side and pull up I can make the position almost perfect, but it doesn't stay in that position of course.

The following photos are of PF view and associated Home Opto (and cam roller) view at each position of the MPF in Test 14. CW and CCW are clockwise and counterclockwise respectively and refer to rotation of the MPF motor spindle as viewed from the front. L and R refer to the position of the cam roller being on the Left or the Right when the MPF is at Middle ("Mid") Level.

When moving CW, the motor stops when the opto becomes Unblocked. When moving CCW, the motor stops when the opto becomes Blocked. It looks to me that the motor turned a slight amount more beyond the point when the opto was completely blocked or unblocked, but I'd like to hear what others think. I checked the tightness of the motor spindle in the cam and the cam doesn't rotate round the spindle when I try to turn it and the set screws holding the cam to the spindle are tight.

1. CCW MidR (Ascend to middle level)
CCW MidR (Ascend)
CCW MidR (Ascend) Home Opto

2. CCW Up
CCW Up
CCW Up Home Opto

3. CCW MidL (Descend to middle level)
CCW MidL (Descend)
CCW (Descend) Home Opto

4. CW Up
CW Up
CW Up Home Opto

5. CW MidR (Descend to middle level)
CW MidR (Descend)
CW MidR (Descend) Home Opto

6. CW Down
CW Down
CW Down Home Opto Opto

7. CW MidL (Ascend to middle level)
CW MidL (Ascend)
CW MidL (Ascend) Home Opto

8. CCW Down
CCW Down
CCW Down Home Opto

Went back today and performed the procedure to eliminate canting again. This time I compressed the sides of the bracket as close together as possible to minimize the wobble, but not so much as to bind up the rollers. The mechanism works smoothly with less wobble, but still settles too low after descending to the Mid Level. I bought a new cam and the roller that inserts on the cam and rolls in the horizontal bracket just to see if replacing these one at a time might help diagnose the problem. I'm running out of ideas, that's for sure.

HA! Thanks for the big laugh...I needed it. I just replaced the cam roller even though the outer and inner diameters were essentially the same as the original, and the diameter was consistent so it was round with no flat spots. As you would predict, it didn't help one bit.

I'll swap out the original cam with the replacement tonight to see if that changes anything. I understand your point about suspecting a cam/opto alignment issue. The MPF is only too low at Mid Level when it gets there by descending, and it might be 2-3mm too high at Mid Level when it rises to get there. Otherwise, I'm thinking I'll take one more crack at the canting prevention procedure before adding washers as you suggest.

Two other guys had posted what seemed to be the same problem -- WonkoTSane on Pinside and Eric Conner on rgp both had Mid Levels being too low in their DW. I think the Pinside thread ended with the Wonko using washers without diagnosing the cause, and Connor found the bracket in his machine was broken at one point and the hack to fix it was causing the issue.

Hey zaza. I like your thinking, but I just tested all components you indicated and all had the expected readings. Thanks for checking in!

Just tried the replacement Dr Who cam from Marco. It looks to be an exact match with respect to the cut outs on the perimeter, but the "D" shaped hole in the middle for the motor spindle is oriented a little differently with respect to the cut outs. It had no effect, good or bad. The MPF is still too low at Mid Level.

The Home Opto looks aligned, responds normally in Switch Edges test, and still does when I flex the wires leading to the opto switch back and forth.

I'm done for tonight. Will try to do some more tomorrow. If not tomorrow, then I won't be back at it until Monday.

OK, I'm back. Thanks guys for the additional thoughts. Since the replacement cam and cam roller didn't affect the problem either way, I replaced the original parts and took some more video and measurements. Please note I have Cliffy protectors on both the MPF and the PF.

Here are the facts:

1. When the Mini Playfield (MPF) is at the Mid Level position irrespective of how if got to the position (CW or CCW, descending or rising), there is consistently about 7mm "slop" in the mechanism. That is, I can lift the MPF to higher position than where it comes to rest. It will sink quickly to the resting position when I release my grip. There is no slop when the MPF is in the Up position, and maybe 1mm or less when in the Down position.

2. When the MPF descends to Mid Level either by CW or CCW direction (and the resulting resting position is too low), the top of the MPF is 38mm above the main playfield (PF). I can then manually lift the MPF another 7mm to the point where the top is 45mm above the PF.

3. When the MPF rises to Mid Level either by CW or CCW direction (and the resulting resting position is good), the top of the MPF is 45mm above the PF. I can then manually lift the MPF another 7mm to the point where the top is 52mm above the PF.

Two videos are linked to show this "slop" and what happens at the cam/home opto relationship.

The first video shows the resting position and "slop" in the MPF mechanism after the MPF descended to Middle Level in the CCW MidL sub-test of Test 14. As stated above, the MPF surface is 38mm above the PF at rest, and 45mm when lifted. Note the DMD showing the home opto is blocked at rest, but will become unblocked during manual lifting of the MPF. Also remember that the cam was moving CCW in this subtest, so blocking of the opto triggered the stopping of the motor.

This second video shows the cam/home opto positions of the MPF positions in the first video above. Initially it shows the cam/opto with the MPF in its resting position (38mm above the PF) and that the home opto is blocked by the cam. Then it shows how the cam moves and the opto switch becomes unblocked when I pull the MPF to it's highest position.

I'll pursue the suggestions made by faz and pinwiz_pa later today, but just wanted y'all to see what I'm seeing right now.

PM

I just had the MPF out. I think some of the slop was due to one or both set screws holding the cam to the arbor not being as tight as they could have been. After tightening up both screws, the cam didn't rotate nearly as much, but it still did. Instead of throwing the whole MPF back into the machine again, I decided to replace the motor while I had it out to address yours and Faz's latest comments at a high level. The arbor in the new motor seemed noticeably tighter in the motor. It didn't turn at all whereas the arbor could rotate just ever so slightly in the original motor and move in and out a short distance a little more readily than in the replacement motor. I placed the cam on the new motor and tightened up the set screws. The cam certainly didn't rotate as much. I placed it back in the machine hoping it would be the cure.

Nope. The resting position Middle Level is still the same at 38mm above the PF. The only thing that changed was the amount of slop. It was reduced from 7mm to 2mm. Rising to Middle Level still sets the MPF at 45mm above the PF. Descending still sets that distance at 38mm. In all cases, I can lift the MPF just another 2 mm.

At Middle Level, what is the distance between MPF (top edge) and PF surface in your machine? Can you pull your MPF up any distance after it settles at Middle Level?

Thanks pinwiz. If you get a chance, do you mind taking a look at the position of your cam relative to the home opto when in MPF Test 14 and after the CCW MidL test has run? That should put the MPF in the Middle Level by descending. I'm interested in knowing whether the cam covers the home opto in your machine as much as it does in mine following that subtest. It still seems to me that the cam is overrunning the home opto when it descends to Middle Level, but I just don't have enough experience with this to be certain.

Thanks pinwiz. That's about 47.6mm which is close to the distance I have after the MPF ascends to Mid Level. I expect faz's measurement will be in the neighborhood too. I'll also check the DW at our pinball club tonight or tomorrow, and recheck my bi directional board too to ensure zaza wasn't on to something as well. It worked perfectly last time and the components all had normal values, but never hurts to check again.

The distance from MPF to PF in our club's DW is 42cm. Lower than I expected, but just high enough for the pinballs to strike the mushroom targets and not the bottom of the MPF. My Bi-Directional board and components checked out fine too.

I revisited the cant procedure amendment and once again made sure the mechanism was all squared up and not bent. The mechanism works smoothly with very little canting.

I'm tired of dealing with this. I think I'll just start adding washers under the main bracket attachment to the MPF or under the support bracket to the PF unless someone has another idea.

Well, I guess I better give closure to this thread. I was tempted to buy another cam and modify the cam windows that control the middle level stopping points by grinding or adding material to the window. I reasoned this modification will cause the opto to either close or open just a hair quicker. But I decided I'm getting fed up with this problem, so I just placed washers between the Support Bracket and the PF to get as close to flush when the MPF is down, but ensure the MPF is still high enough at middle level so the balls can hit targets. It took a while, but it is working well now.