(Topic ID: 289589)

Need feedback - CFTBL ejector issue - Odd 70V scope curve

By Ashram56

7 months ago


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  • Latest reply 7 months ago by Ashram56
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#1 7 months ago

Good morning everyone,

Posting here to reach a broader audience than on the CFTBL owner thread.

For quite a while I've been encountering a random issue, now much more persistent, with the ejector in the VUK of my Creature. This ejector is powered by a coil, driven by a transistor on the power board, and the 70V power rail. The issue is that the VUK does not have enough force to propel the ball into the wire ramp (at least 4 out of 5)

I've cleaned up the mechanics, changed the sleeve, even replaced the coil, to no avail. So I started to try to debug at the power board level and took an oscilloscope shoot of both end of the coil, picture attached.

From this scope shoot, you can see the drive transistor is working perfectly, the curve is a nice inversed square.
The other curve however is the 70V rail, which "should" stay flat (at least in theory).

So I changed BR3 rectifier and C8 capacitor, as these are pretty much the only components in the schematics between AC and the coil itself, at least with regards to 70V rail, but this did not change the behaviour one bit.

Given that C8 is a relatively low value capacitor (150uF), I'm starting to believe that this curve is actually normal given the huge power drain when the coil energize, and I've been looking at the wrong direction

Could someone therefore please comment on whether such a curve is expected for a 70V power rail on a WPC89 power board ?

If not, then I will keep focusing on the power board
If yes, then this means the issue is at the coil, mechanical or otherwise

Thanks and regards
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#2 7 months ago

Let's take a step back. What is the actual issue you are having.

#3 7 months ago

As noted in my original post: the ejector does not have enough force to propel the ball into a wireramp, so it falls back into the VUK, which then tries to eject it agin. For those familiar with CFTBL, this is the 'slide' ejector, at the top right of the playfield, just below the bumpers.

A short video here :

#4 7 months ago

I'm relatively sure your power supply is fine. I've got the same thing going on with my creature and periodically I need to make mechanical adjustments to either/both the VUK under the PF or the position of the wire form to get it to work again. I'd suggest using a phone to take a video of the issue in SLO-MO (on the iPhone anyway) which has a high frame rate (240 fps). This will allow you to see if the trajectory of the ball causes it to glance off the wire and "rattle" around in the form causing it to loose energy and fail to complete the launch. The wire form should obviously guide the ball around the curve gently changing it's direction.

That being said my wire form is also F'd up. It broke and was welded back together, poorly I might add. (Anyone have one for sale?) Something I'll have to deal with when I get to a complete tear down.

#5 7 months ago
Quoted from bakerhillpins:

I'm relatively sure your power supply is fine. I've got the same thing going on with my creature and periodically I need to make mechanical adjustments to either/both the VUK under the PF or the position of the wire form to get it to work again. I'd suggest using a phone to take a video of the issue in SLO-MO (on the iPhone anyway) which has a high frame rate (240 fps). This will allow you to see if the trajectory of the ball causes it to glance off the wire and "rattle" around in the form causing it to loose energy and fail to complete the launch. The wire form should obviously guide the ball around the curve gently changing it's direction.
That being said my wire form is also F'd up. It broke and was welded back together, poorly I might add. (Anyone have one for sale?) Something I'll have to deal with when I get to a complete tear down.

Thanks for that info, I'll try that

#6 7 months ago

I had a similar issue on Taxi and is the first time this behavior ever occurred - relative to the fix, this fix might be worth a try as it's simple and cheap. Ball would sometimes eject the ball to shooter lane no problem. Other times it would try several times but not enough umph. Replaced coil, same. Put old coil back. Checked connections an cleaned jacks and plugs. Same. Replaced driver and pre-driver. Fixed. I always assumed that a failed driver would lock on a coil or not drive a coil at all. Not so apparently.

#7 7 months ago
Quoted from Seamlesswall:

I had a similar issue on Taxi and is the first time this behavior ever occurred - relative to the fix, this fix might be worth a try as it's simple and cheap. Ball would sometimes eject the ball to shooter lane no problem. Other times it would try several times but not enough umph. Replaced coil, same. Put old coil back. Checked connections an cleaned jacks and plugs. Same. Replaced driver and pre-driver. Fixed. I always assumed that a failed driver would lock on a coil or not drive a coil at all. Not so apparently.

That was my idea originally, and since I have an oscilloscope that's the reason I took my scope shoot. And from that scope shoot I have no reason to believe the driver transistor is at fault (this is the inversed square waveform). I could change it indeed (and will if I can't find any other reason for the failure), but if it works I must admit that will contradict every single bit of electronics theory I have learned Or there's something I'm missing.

#8 7 months ago

Ashram56 Is the scope shot you posted a successful attempt at ejecting the ball or a failed attempt?

#9 7 months ago
Quoted from Fifty:

ashram56 Is the scope shot you posted a successful attempt at ejecting the ball or a failed attempt?

Neither, there was no ball (as I have to lift the playfield to put my probe there). Plus the issue is pretty much persistent now, and I got this waveform everytime.

#10 7 months ago
Quoted from bakerhillpins:

I'm relatively sure your power supply is fine. I've got the same thing going on with my creature and periodically I need to make mechanical adjustments to either/both the VUK under the PF or the position of the wire form to get it to work again. I'd suggest using a phone to take a video of the issue in SLO-MO (on the iPhone anyway) which has a high frame rate (240 fps). This will allow you to see if the trajectory of the ball causes it to glance off the wire and "rattle" around in the form causing it to loose energy and fail to complete the launch. The wire form should obviously guide the ball around the curve gently changing it's direction.
That being said my wire form is also F'd up. It broke and was welded back together, poorly I might add. (Anyone have one for sale?) Something I'll have to deal with when I get to a complete tear down.

So I adjusted the wireramp (kind of randomly), by pulling the ramp as low as I could (so the ball would be closer to the wire ramp when being ejected). It seems to have improved a lot, so that could have been the cause indeed.

I'm still puzzled at the scope shoot though, so if someone can take a similar measurement, at least as a reference point

Cheers

#11 7 months ago

The filter cap on that voltage is quite small.

If you have close to a zero load on the coil voltage then the cap is big enough to hold it high consistently. It is a DC voltage under light loads.

If you have a heavy load (e.g. any coil) then the cap is not big enough to hold it high and you will have a rectified AC voltage as presented by the output of the full wave bridge rectifier. With a full wave bridge rectifier - you should be seeing 120 pulses per second (assuming your mains power is 60Hz). This is what you see.

#12 7 months ago
Quoted from Ashram56:

pulling the ramp as low as I could (so the ball would be closer to the wire ramp when being ejected).

I'm not quite sure I understand the adjustment you made but if it improved then that's a start. I'd still suggest using the video footage to help with understanding the ball's behavior when in the wire form.

In my situation I had to adjust such that the ball contacted the outer "wall" of the wire form earlier in it's upward trajectory. Since it curls toward the top of the playfield I had to move it up toward the bumpers. The ball is now effectively traveling parallel to the wire and right next to it. Thus when the ball finally makes contact with the wire form it's change of direction is more gradual (like a loop shot) rather than banging into the corner. I.e. - It's angle of incidence is much greater.

#13 7 months ago
Quoted from G-P-E:

The filter cap on that voltage is quite small.
If you have close to a zero load on the coil voltage then the cap is big enough to hold it high consistently. It is a DC voltage under light loads.
If you have a heavy load (e.g. any coil) then the cap is not big enough to hold it high and you will have a rectified AC voltage as presented by the output of the full wave bridge rectifier. With a full wave bridge rectifier - you should be seeing 120 pulses per second (assuming your mains power is 60Hz). This is what you see.

That's the conclusion I reached, however I'm surprised at such a design. That said, it seems that at least for a good 5 to 10ms the voltage différence is still high, and if the coil energize and the plunger reacts in less than 10ms, then even such a curve would not have an impact on the actual output. That's why I was hoping someone would have done a similar measurement to confirm/infirm this theory

Quoted from bakerhillpins:

I'm not quite sure I understand the adjustment you made but if it improved then that's a start. I'd still suggest using the video footage to help with understanding the ball's behavior when in the wire form.
In my situation I had to adjust such that the ball contacted the outer "wall" of the wire form earlier in it's upward trajectory. Since it curls toward the top of the playfield I had to move it up toward the bumpers. The ball is now effectively traveling parallel to the wire and right next to it. Thus when the ball finally makes contact with the wire form it's change of direction is more gradual (like a loop shot) rather than banging into the corner. I.e. - It's angle of incidence is much greater.

I actually did the reverse. So honestly I'm not sure if this change had anything to do with the improvements, or if this coincidence

I'll try the high speed video capture

Cheers

#14 7 months ago

Well that was coincidence, as the issue came back. Not as persistent as last week, but still it's back.

I'll take a slow motion capture (once my son finds my camera !! - my phone can't capture at 240fps)

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