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(Topic ID: 259141)

Resistor Burn-Up Mata Hari


By RetroRyan

9 months ago



Topic Stats

  • 17 posts
  • 4 Pinsiders participating
  • Latest reply 9 months ago by RetroRyan
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    TIP102.jpg

    #1 9 months ago

    I have a resistor burning up on a Mata Hari solid state. Resistor R18 which is on the outhole kicker circuit. If I disconnect the wire to the outhole kicker coil, the resistor does not burn. I replaced the wire from point to point, it still burns. I have also fixed/replaced:
    1. Playfield fuse holder and fuse.
    2. All fuses at power board and fuse on solenoid driver board.
    3. Molex connector at J1 on solenoid driver board
    4. C4 capacitor and CR4 diode on same circuit at solenoid driver board.
    5. Replaced coil at outhole with knocker coil in game (basically the same coil)
    6. New doide at outhole kicker coil and EOS switch at outhole.
    7. Replaced U1 chip

    MPU works properly and gives all 7 flashes. With disconnected outhole coil game starts up and plays perfectly (minus kicker not working of course).

    Does anyone have any idea what could keep causing this resistor to burn up? Thanks!

    #2 9 months ago
    Quoted from RetroRyan:

    Does anyone have any idea what could keep causing this resistor to burn up?

    Your Q4 driver transistor is probably shorted from the base to collector legs which is putting 43 volts across that R18 resistor.

    If you haven't got any spare driver transistors (TIP102 is a common replacement), borrow one from location Q17 or Q18 which are unused on your game.

    #3 9 months ago

    I have a spare board for parts so I can Harvest a transistor there. I believe I tested the Q4 transistor earlier tonight and showed good readings. Ground at center pin and then readings at outside pins. Does this eliminate that transistor as a possibility? I will double check to be certain

    #4 9 months ago
    Quoted from RetroRyan:

    I believe I tested the Q4 transistor earlier tonight and showed good readings. Ground at center pin and then readings at outside pins. Does this eliminate that transistor as a possibility?

    Well the center transistor leg is the collector, normally when testing transistors the common leg is the base to test against and then the collector to emitter. Note this is a "darlington" transistor (two in one) that has a reverse internal diode from collector to emitter - see the internal diagram below:

    Anyway the transistor could be breaking down under voltage. That R18 resistor can only burn if it's seeing 43V solenoid voltage via a shorted C4 capacitor (you said you changed it already) or transistor Q4, or by some some soldering mistake on the board.

    TIP102.jpg

    #5 9 months ago

    Quench, great advice. Interesting that that transistor would test okay but would fail under load. I harvested one from a spare board that I have and sure enough the resistor is holding perfectly. Now I'm left with one remaining problem. The outhole kicker coil is not firing when a game is started. There is adequate voltage to the coil and switch at the outhole has voltage and is gapped correctly. Everything else seems to be working perfectly. This must also be an issue with the board? Thanks in advance for your help.

    #6 9 months ago
    Quoted from RetroRyan:

    Quench, great advice. Interesting that that transistor would test okay but would fail under load. I harvested one from a spare board that I have and sure enough the resistor is holding perfectly. Now I'm left with one remaining problem. The outhole kicker coil is not firing when a game is started. There is adequate voltage to the coil and switch at the outhole has voltage and is gapped correctly. Everything else seems to be working perfectly. This must also be an issue with the board? Thanks in advance for your help.

    You can ground the tab of Q4 to see if it makes the solenoid pull in. That would check to see if the connection between the driver board and coil is ok. otherwise the ca3081 and/or 74154 might have failed with Q4.

    I would make sure the signal leaves the U2 74154 chip (Q4 comes 74154 pin 7). If it does but the solenoid still does not fire the CA3081 at U1 is probably bad.

    If just one circuit in the CA3081 is bad you can bodge in a 2n4401 as the ca3081 are obsolete. In the schematic they draw the CA3081 as a transistor noting the pin numbers which you can match up to a 2n4401 pin out. Or borrow a ca3081 from your donor board.

    #7 9 months ago

    Thanks for the info. Grounding Q4 does not fire the coil. Ill try to figure out how to test the pins listed above and report back. Thank you!

    #8 9 months ago

    I have spare chips for both U1 and U2. Is there a way to test pin 7 on U2 with a DMM or will this require a logic probe?

    #9 9 months ago
    Quoted from RetroRyan:

    Grounding Q4 does not fire the coil.

    This means the problem is downstream from the transistor so hold off testing U1/U2 for the moment.
    The metal tab of transistor Q4 connects directly to the outhole coil on the brown-yellow wire coming off the rectifier board from connector J1 pin 5. Somewhere between the middle leg of the Q4 transistor and the coil you have a bad connection which you'll need to find. Note the metal tab of Q4 is the same as the middle leg of Q4.

    #10 9 months ago

    I jumpered pin 5 on J1 from solenoid driver board direct to lug on outhole kicker coil and ran solenoid test through diagnostic system. Coil did not fire. Next step? And thanks again you guys for all the input.

    #11 9 months ago

    Maybe i should jumper metal tab of Q4 direct to coil and retest? This could isolate a problem from molex connector at j1 to coil correct?

    #12 9 months ago
    Quoted from RetroRyan:

    Maybe i should jumper metal tab of Q4 direct to coil and retest? This could isolate a problem from molex connector at j1 to coil correct?

    Yes, try that - make sure you don't touch the yellow wire on the coil which is 43 volts. You want to touch the brown-yellow wire on the coil.

    #13 9 months ago

    Still did not fire. What else could it be?

    #14 9 months ago

    Is the coil good? If you use a DMM to read resistance across the 2 cool lugs, what value do you see?

    #15 9 months ago

    I did test the coil and it was reading 10.7 ohms. It was also showing 44 volts at the power lug.

    #16 9 months ago

    I must be missing something. It sort of seems like all roads lead to Q4 at this point. I wonder is there a way to bypass Q4 direct to the coil? Maybe from power board? This way maybe we could determine if problem is at the coil or somewhere in solenoid driver board. Just throwing this out as an idea. Thanks again!

    #17 9 months ago

    Dear participants of this thread, you guys are AWESOME! After doing everything you guys mentioned in this thread I circled back and added yet another replacement transistor at Q4 since everything seem to be leading back to there. Whabam! It works! Not sure if it wasn't soldered in quite well enough or if the first transistor I put in was no good but either way it's a done deal now. Thanks to you all for your help!

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