(Topic ID: 193444)

Bally locked on bumper coil (not transistor)


By JReedie

2 years ago



Topic Stats

  • 24 posts
  • 6 Pinsiders participating
  • Latest reply 1 year ago by StratDoc
  • Topic is favorited by 2 Pinsiders

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    Medusa_SDB_LowerRightPopBumper_Voltages.jpg
    Medusa_SDB_LowerRightPopBumper.jpg
    XandO_SwitchMatrix.jpg

    #1 2 years ago

    My 1985 Bally Xs & Os has a locked on bumper coil that after about 2 seconds of powering up the machine blows the 1A fuse underneath the playfield. I changed the transistor that controls the naughty bumper coil and its not shorted out. Neither is the diode before the transistor and i have also replaced the bumler coil in question with a brand new one without successfully fixing the issue. I have an Alltek board running the machine if that helps at all.

    Id greatly appreciate any ideas you all may have.

    #2 2 years ago

    Which Pop Bumper is it?
    Was/is the diode on the coil measuring good?

    On the SDB, it might be a faulty U3 transistor array or the 74L154 causing the transistor driving the Pop Bumper to lock on.

    #3 2 years ago

    It can also be the 74L154 binary-decoder or CA3081 transistor-array ICs. I would start with socketing and replacing the CA3081 (these do fail), and then the decoder. These ICs are not expensive..

    #4 2 years ago

    It can also be a simple short. Look at the leads for the solenoid and take a good look where the bottom of the play field meets the lock down bar receiver. Sometimes a wire just gets a little out of place.

    #5 2 years ago
    Quoted from Quench:

    Which Pop Bumper is it?
    Was/is the diode on the coil measuring good?
    On the SDB, it might be a faulty U3 transistor array or the 74L154 causing the transistor driving the Pop Bumper to lock on.

    It is the left pop bumper which is driven by Q12

    #6 2 years ago

    Disconnect the J5 connector from the Solenoid Driver Board (SDB) which will disconnect that Pop Bumper so you no longer blow the playfield fuse.

    Measure the voltages on the SDB at:
    a) Pin 14 of U2 (74L154)
    b) Pin 10 of U3 (CA-3081)
    c) Pin 9 of U3 (CA-3081)
    d) The banded side of diode CR12 (near transistor Q12)

    Report back your measurements.

    #7 2 years ago
    Quoted from Quench:

    Disconnect the J5 connector from the Solenoid Driver Board (SDB) which will disconnect that Pop Bumper so you no longer blow the playfield fuse.
    Measure the voltages on the SDB at:
    a) Pin 14 of U2 (74L154)
    b) Pin 10 of U3 (CA-3081)
    c) Pin 9 of U3 (CA-3081)
    d) The banded side of diode CR12 (near transistor Q12)
    Report back your measurements.

    Thank you for your help so far!

    Pin 14 of U2 = 4.14V
    Pin 10 of U3 = 4.14V
    Pin 9 of U3 = 2.01V
    Diode CR12 = 1.31V

    #8 2 years ago

    U3 is a transistor array. The voltage measured on pin 10 of U3 (base pin of a transistor within the array) is excessively high most likely because pin 10 has internally gone open circuit. This is resulting in pin 9 of U3 (collector pin of the same transistor within the array) to be pulled high which is always activating the Q12 transistor down stream and locking on the Pop Bumper solenoid.
    Normally, when the solenoid is not being selected to activate, pin 10 will sit at its highest level of around 0.8 volts and pin 9 should be near zero volts which leaves transistor Q12 switched off.

    Replace the CA-3081 device at U3.

    If you're really really desperate to get it going while you wait for replacement parts, you can temporarily swap U3 with the CA-3081 at U4. U4 is not driving any solenoids with that faulty transistor within the array. Just keep your fingers crossed no other transistors within the U3 array are faulty if you do this...

    Good luck!

    #9 2 years ago

    Another thing you can do as long as the common emitter leg is not shorted is to snip off other offending legs of and wire in a 2n4401.

    #10 2 years ago
    Quoted from Quench:

    U3 is a transistor array. The voltage measured on pin 10 of U3 (base pin of a transistor within the array) is excessively high most likely because pin 10 has internally gone open circuit. This is resulting in pin 9 of U3 (collector pin of the same transistor within the array) to be pulled high which is always activating the Q12 transistor down stream and locking on the Pop Bumper solenoid.
    Normally, when the solenoid is not being selected to activate, pin 10 will sit at its highest level of around 0.8 volts and pin 9 should be near zero volts which leaves transistor Q12 switched off.
    Replace the CA-3081 device at U3.
    If you're really really desperate to get it going while you wait for replacement parts, you can temporarily swap U3 with the CA-3081 at U4. U4 is not driving any solenoids with that faulty transistor within the array. Just keep your fingers crossed no other transistors within the U3 array are faulty if you do this...
    Good luck!

    Thank you so much for your help. I've just ordered a new chip, fingers crossed it will fix the issue. I shall report back once it arrives and is fitted.

    #11 2 years ago
    Quoted from Quench:

    U3 is a transistor array. The voltage measured on pin 10 of U3 (base pin of a transistor within the array) is excessively high most likely because pin 10 has internally gone open circuit. This is resulting in pin 9 of U3 (collector pin of the same transistor within the array) to be pulled high which is always activating the Q12 transistor down stream and locking on the Pop Bumper solenoid.
    Normally, when the solenoid is not being selected to activate, pin 10 will sit at its highest level of around 0.8 volts and pin 9 should be near zero volts which leaves transistor Q12 switched off.
    Replace the CA-3081 device at U3.
    If you're really really desperate to get it going while you wait for replacement parts, you can temporarily swap U3 with the CA-3081 at U4. U4 is not driving any solenoids with that faulty transistor within the array. Just keep your fingers crossed no other transistors within the U3 array are faulty if you do this...
    Good luck!

    I fitted the new chip and the bumper that was shorting and blowing the playfield fuse now works however the lower bumber now triggers the left hand one as well. And the lower of the 3 bumpers doesnt fire when hit. But when going throigh the solenoid test all 3 work perfectly. Any ideas at all how to repair this?

    Thanks again.

    #12 2 years ago

    Looks like you've got an issue in the switch matrix.

    Can you remove all balls from the game and make sure all drop targets are raised.

    Go to switch test mode.
    Does it report "0" in the Ball in play display?
    When you activate the lower pop bumper switch with your finger does the game report 18 or 19 in the player displays?
    And what number is displayed when you activate the left pop bumper switch with your finger?

    #13 2 years ago
    Quoted from Quench:

    Looks like you've got an issue in the switch matrix.
    Can you remove all balls from the game and make sure all drop targets are raised.
    Go to switch test mode.
    Does it report "0" in the Ball in play display?
    When you activate the lower pop bumper switch with your finger does the game report 18 or 19 in the player displays?
    And what number is displayed when you activate the left pop bumper switch with your finger?

    Both are displaying 18 when in the switch test

    #14 2 years ago

    Ok if you've got the manual, go to the switch test number page 17 and activate each switch one at a time starting from switch #40 working backwards to switch #01 (it's important you do it backwards).

    Report back the details of which switches are reporting the wrong number in the switch test.

    #15 2 years ago
    Quoted from Quench:

    Ok if you've got the manual, go to the switch test number page 17 and activate each switch one at a time starting from switch #40 working backwards to switch #01 (it's important you do it backwards).
    Report back the details of which switches are reporting the wrong number in the switch test.

    Switch 27 is showing 26
    19 is showing 18
    3 is showing 2

    So 2 drop targets are registering the same, 2 standups are registering the same as well as 2 bumpers. This all happened since changing the chip at U3 could that be the vause kf the problems?

    #16 2 years ago
    Quoted from JReedie:

    This all happened since changing the chip at U3 could that be the vause kf the problems?

    No. The chip at U3 on the SDB is completely unrelated to the switches.

    You've got a short between switch return line "I2 and "I1" shown circled in red below.
    Firstly, make sure the three coin slot switches on the coin door are in the open position and not stuck closed.
    Check the capacitors circled in green on the switches shown below and make sure they aren't short circuited.
    Then check the diodes circled in blue on those switches, again looking for any that are shorted.
    Let us know what you find.
    .
    XandO_SwitchMatrix.jpg

    #17 2 years ago
    Quoted from Quench:

    No. The chip at U3 on the SDB is completely unrelated to the switches.
    You've got a short between switch return line "I2 and "I1" shown circled in red below.
    Firstly, make sure the three coin slot switches on the coin door are in the open position and not stuck closed.
    Check the capacitors circled in green on the switches shown below and make sure they aren't short circuited.
    Then check the diodes circled in blue on those switches, again looking for any that are shorted.
    Let us know what you find.
    .

    I went through and checked everything, turns out it was a shorted coin chute switch. I desoldered the wires going to it and everything is working perfectly. Shot a brilliant first game on the machine too!

    Thank you so much for taking the time to help me out

    8 months later
    #18 1 year ago

    I am resurrecting this thread because I am having a similar problem with a Medusa. The bottom right pop bumper locks on when the game is started and blows the playfield fuse. I have replaced the q14 transistor and resistor and installed a new coil on the pop bumper.

    I followed Quench's advice and tested the following voltages on the SDB. Here are the measurements. They appear to be okay.

    Measure the voltages on the SDB at:
    a) Pin 14 of U2 3.68vdc
    b) Pin 10 of U3 .92vdc
    c) Pin 9 of U3 .55vdc
    d) The banded side of diode CR14 1.28vdc

    Thanks in advance for the advice.

    #19 1 year ago
    Quoted from StratDoc:

    I am resurrecting this thread because I am having a similar problem with a Medusa. The bottom right pop bumper locks on when the game is started and blows the playfield fuse.

    ....

    Measure the voltages on the SDB at:
    a) Pin 14 of U2 3.68vdc
    b) Pin 10 of U3 .92vdc
    c) Pin 9 of U3 .55vdc

    Hi,
    The measurements you've made on pin 14 of U2 and pins 9 and 10 of U3 drive the left slingshot.

    For the lower right pop bumper you want to measure the voltages on pin 10 of U2 and pins 13 and 14 of U3.
    .

    Quoted from StratDoc:

    d) The banded side of diode CR14 1.28vdc

    Voltage here on the banded side of the CR14 diode indicates the driver transistor Q14 is being activated (locked on), possibly by a malfunctioning U3.

    Medusa SDB Lower Right Pop Bumper circuit

    #20 1 year ago

    Quench,

    Thank you. I have should have known that - still learning.

    How do you know what the correct voltages should be at the different pins and locations?

    #21 1 year ago
    Quoted from StratDoc:

    How do you know what the correct voltages should be at the different pins and locations?

    The part of the Solenoid Driver schematic I've highlighted above is essentially replicated for all solenoids.
    See the below diagram for indicative voltages when the machine is powered on and idle.

    The banded side of diode CR14 (right leg shown in the diagram below) where you measured 1.28V is connected to the "base" pin of transistor Q14. Consider transistors base pin like an input pin.
    When the game is idle, the base pin of those Q driver transistors should have near zero volts meaning they're switched off resulting in their solenoids not being activated.

    When those Q driver transistors have around 1.2V on the base pin, that switches them on and activates the respective solenoid.
    None of the Q driver transistors driving momentary solenoids should have a constant 1.2V on the base pin.
    Momentary solenoids are selected to activate for only a very brief time - typically 0.3 - 0.4 seconds.

    Q driver transistors driving Continuous coils on the other hand can and do have constant 1.2V on the base pin when they switch on things like flipper enable relays, coin lockout coils, playfield gates, etc. The specific Q transistors wired for continuous coils are Q15, Q17, Q18 and Q19 which are listed on the top right of the SDB schematic.
    .

    Medusa_SDB_LowerRightPopBumper_Voltages.jpg

    #22 1 year ago

    This is really helpful. Thanks!

    I replaced U3 and everything worked fine for a while. Then the same pop bumper - bottom right decided to quit working. Q14 had failed. I replaced it and all was good for a while and then Q14 failed again.

    #23 1 year ago

    Have you replaced the diode on the pop bumper solenoid? Does the coil measure good (around 11 ohms resistance)?
    How about diode CR14 on the SDB, did you replace it when replacing U3?

    #24 1 year ago

    It is a new coil with diode so it should be good. I did not replace the cr14 on the sdb. Will do that and report back.

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