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(Topic ID: 211312)

Gottlieb Flipper Coil Resistance Issues

By quinntopia

2 years ago

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  • 16 posts
  • 4 Pinsiders participating
  • Latest reply 2 years ago by quinntopia
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    #1 2 years ago

    Putting my Sinbad back together, I am checking coils and connections with my DMM.

    I used a Flipper rebuild kit from Marco on all four flippers, including brand new A-17875 coils.

    As I check the resistance, the two flippers on the RIGHT side give me an expected reading of 2.9 ohms (Sinbad has four; two on each side). All good!

    However, when I check the resistance on the LEFT side flippers, the Ohm reading for these coils is 10.2! Yikes!

    So I’m confused! Why would the coils on the left side have a resistance more than three times the right side set of flippers?

    Clearly, something is wrong.

    Note that the entire playfield is disconnected from all boards (power supply/driver board) and there are no connections to any power at all.

    The only thing that I know might suspect, is that when I was reattaching these flippers, my older disassembly photos seemed to indicate that one of the EOS switch wires was going to an outer lug instead of the center lug, so I made the swap to match the connection of my photos of the original (pre-rebuild) flipper connections (I.e. the “top” wire on the EOS was on an outer lug, and the “bottom” wire on the EOS went to the center lug: these were swapped to match my photo).

    As I Google the internet looking for some ideas (and not really knowing exactly what to look for in a wiring diagram) I thought I would ask here to see if anyone might know what could cause such a high and inconsistent ohm reading for brand new coils.

    Thanks in advance!

    #3 2 years ago
    Quoted from wayout440:

    Are you checking the coils with wires and diodes removed from them? If the coils has connections to it, in circuit components can interfere with accurate measurement.

    No, and I recall that Clay says this too but I was trying to avoid resoldering everything. Unfortunately, I don't think I have a choice. Thanks!

    #4 2 years ago

    Okay, I may have found one issue. It appears that when I rebuilt the flippers, the banded sides of the diodes were not facing the same direction and two of them are in the wrong direction. Since I need to remove the coils to check them anyway, I'm going to turn the diodes to face the correct direction.

    #5 2 years ago

    Update: Replaced and correctly oriented two diodes on two coils that were facing the wrong way.

    As I have a 'parts' Sinbad, I was able to compare my wiring with the unmodified original harness and its routing to the coils. Basically had some wires that went to the center tab that should have been on the 'power' tab on the coil. Now everything matches the unmodified Sinbad.

    When I tested the resistance of one of the RIGHT side coils without any connections it read 40 ohms. Wow. What's that! Clay mentions that 40 ohms is the 'hold' resistance, but not sure that's what I should get with my standard resistance setting.

    So what do I see now with everything corrected?

    The two RIGHT coils are still 2.9 ohms but both the LEFT coils now read 5.5/5.6.

    Note that when I test the resistance of the common (black wire) to the CENTER tab on either the LEFT coils I do get a nice 2.8/2.9 ohms.

    Anyone have any ideas? Again - all wiring harnesses are disconnected.

    #7 2 years ago
    Quoted from Inkochnito:

    Open all EOS switches and try again.
    Just put a piece of paper between them.
    I've had this kind of problem with Joker Poker.
    Right flipper was good and the left flippers were both bad, or so I thought.
    I opened both EOS and measured again and now all is good.

    Finally got around to doing a proper test. I have since installed the playboard and connected all the harnesses to the CPU/Boards (good news there BTW)

    With all four EOS switches open (business cards inserted) I now read a consistent 20.8 ohms across each of the four outside tabs.

    With the EOS switches closed (no business cards) I read the following from each coil (going from LEFT to right as a player would see the flippers, with the left side being the problem side above). As you can see from the below, the resistance is now different. Instead of the 5.5 I had previously on the left flipper coils, they are down to 3.1. But the right side is not lower (dropping from 2.9 t0 2.1/2.2).

    I did power it up and, as I might have accepted, the left side coils didn't work, the right did. There may be other issues with flipper button switches, but I'm still stuck with the strange coil readings.

    Screen Shot 2018-03-09 at 1.06.31 PM (resized).png

    #8 2 years ago

    Quick update...given that the above were all in some qualifying range of resistance, I powered up to check operations.

    From Left to right, Flippers 1, 3, and 4 all worked, but but Flipper #2 (shown above with 3.1 ohms resistance) would not. Nothing.

    After several button presses, both left flippers would stop working and would generate a hum. No fuses blown or smoke!

    And I'm not sure if this related, but once the flippers activate after the buttons being pressed, the flipper movement back to the resting position was very slow. I don't know if I need to tighten up the spring tension or if this indicates part of the problem.

    #9 2 years ago

    Took #2 apart, removed the coil, checked for any obvious signs of wear or shorts, resoldered everything and yet still get these crazy ohm readings. 20.9 on the two left, 1.8 on the two right.


    Anyway, powered up, gave a few taps, and slowly and consistently all the flippers start to work!

    What? I’m stumped. My best and uneducated guess was that because it was a brand new coil that perhaps it needed some power to run through it.

    I don’t know. But it works now!

    #11 2 years ago
    Quoted from GRUMPY:

    I don't think this is wired correctly. The power wire should go toward the silver band on the diode. The EOS wire should not connect to the power wire it should connect to the ground wire. So the coils in your pic either have the power wires connected wrong or the EOS wires are connected wrong. I'm leaning towards the EOS wire.

    I may look into that. The banded side of the diodes are on the power lines (green or purple) but that may not be clear in the photo. I need to check the EOS connections. I feel okay about those as they were connected to the power lines and the center stubs on the original machine, but that might be a change made by previous owner (it was non working) so I might followed someone’s mistake. I have a wire harness from a spare Sinbad that I can check to see how that was wired. Pretty sure I tried to mimic both my photos from disassembly as well as the spare, but easy to miss!

    #14 2 years ago

    Thanks for the explanation on the coil resistance in parralel. I suspected this might be an issue, but as I still consider electricity a dark art best left to wizards and practitioners of science, I wasn't sure.

    The good news is they all work really well now, except the rebuild kit springs are pretty slack and needed some adjustments.

    In all sincerety thanks for your help!

    #16 2 years ago
    Quoted from wayout440:

    Glad you got it. Electricity is not a dark art, but a subject that you just need to spend a little time learning about. I mentioned way early in the thread that disconnecting the coils to get an accurate measurement would likely be required...I just didn't mention why.

    Lol, we’ll, I mean a dark art sarcastically of course!

    These are the sort of experiences where I learn the most (and believe it or not, even starting to figure out the wiring diagrams!).

    Thanks for the illustration above, that helps to illustrate that each coils resistance is “combined”. I’ve actually created led circuits in another hobby where different resistors are needed dependent on the number of LEDS used, so I should have considered something similar here.

    Clay’s guide and other online resources all cover standard two flipper games so my initial confusion was also increased because I had additional coils in parallel!

    My conclusion is that my initial soldering was bad on the power and common tabs. Once I removed the coil and did a much cleaner solder when reattached, that solves the problem.

    So three things to learn from this:

    1. Coils in parallel change the resistance compared to coils not in parallel.
    2. Connections, connections, connections.
    3. The dark lord Sauron is controlling the world through the witchcraft of electricity and his minions have taken over pinball (ahem...sarcasm! )

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