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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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 :

Thanks for that info, I'll try that

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.

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.

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

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

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

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)