(Topic ID: 232941)

Phantom scoring with drops on Mata Hari

By zombywoof

5 years ago


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#1 5 years ago

Not always, but often enough, I get run on scoring associated with the drop targets on my SS Mata Hari. I might hit a target and hear twice the number of chimes as normal. Alternately, the ball could be in play elsewhere on the playfield and chimes and points rack up as if a target or targets just dropped. I thought for sure it was a bad diode on one or more of the drop target switches. I just desoldered a leg free on all eight diodes and checked each one out of circuit. Much to my surprise, they all check good.

I've started trying to isolate switches by inserting a sheet of paper between the leafs. With all but the lower right switch blocked I get the following behavior. If I drop the one active target, it scores normally. If I drop the disabled target next to it, it also chimes and scores. The same is true if I drop the upper right target in the same bank. What does this tell me, and how should I proceed?

#3 5 years ago

If they are repros, they were done by a previous owner. I've had the machine about five years or so. They don't look exactly like the ones that Marco is selling. They might be original.

Continuing with my switch isolation, I blocked all but one drop switch in turn for each of the eight targets. I found that if either the bottom target on the right or the second from the top on the left is active I get fantom scoring, even from targets that have their switches blocked. With these two targets blocked and all others active, I have no run-on or phantom scoring. I went ahead and replaced the diodes on these two targets with no change in behavior. The switch gaps look good and are consistent with the other targets.

#6 5 years ago
Quoted from dothedoo:

Unblock all of the switches, start a game, knock down a target, then pound on the playfield. If it scores every time you pound then either one or more of the switches is gapped too close or the target can't press on the switch hard enough to keep it closed.

I just did this. No scores with a target down and pounding the playfield tight between the two banks.

#9 5 years ago

The switches are clean and gapped correctly. I’m going to go ahead and replace the remaining switch diodes. Since the switches are wired in series, perhaps a bad diode upstream from the problem drops is causing the error? I’ll report back once i’ve Had a chance to open it back up.

#11 5 years ago

@mrm_4, thanks for pushing me to just replace all of the diodes. I don’t usually go for the shotgun approach, but given that all of the previously installed diodes tested good, I don’t know how I would have narrowed it down further than I did. I won’t argue with results. Based on brief testing, the phantom scoring seems to be resolved. I do see an occasional double score on a drop, but I think this is just the target bouncing on the switch, and can be largely dialed out with further adjustment.

@ocd_pinball, just curious if this would also apply to the Alltek MPU that is installed in this machine? I’m not knowledgeable enough to know how closely Dave followed the original design.

Finally, I decided that while I had the machine open and the solder station handy I would replace a cracked pop bumper skirt. Boy, I forgot what a royal PIA this can be on these old Ballys.

1 week later
#42 5 years ago

@BigAl56, thank you for taking the time to post here. Your unique insight is invaluable and greatly appreciated. You were at Bally during what I consider the zenith of pinball history.

As for Rom version, I cannot say for sure. My machine had an aftermarket Alltek Ultimate MPU when I got it. I would assume that it uses the most recent ROM file available, but cannot say with certainty.

Replacing all of the drop switch diodes solved my phantom scoring phenomenon. (@mrm_4, mine were wired just like yours, so you can increase your data set). My wife and I played a bunch of Mata Hari this past weekend. There was one, maybe two instances where a particularly hard drop caused a double score, but these were truly isolated events. I would consider this to be expected behavior for this era mech. I don't think it is worth the time and aggravation to try and dial that out, even if possible.

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