(Topic ID: 277016)

Taxi - Special Solenoid Driver blowing

By thedefog

9 days ago

Topic Stats

  • 21 posts
  • 4 Pinsiders participating
  • Latest reply 11 hours ago by thedefog
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    #1 9 days ago

    This is probably simple, but better to ask vs replacing a lot of TIP102's, pre-drivers, and logic over and over again.

    Special solenoids aren't locking on at pwr on here, but Q75 blows up when triggered.

    I initially replaced q75 as it was blown previously. Replaced the 4401 pre-driver and 7402 @ u45 as well, as the high signals on IJ18 were not present. Everything else tested fine in the area. Tested out U50 and U49 as well. Pop coil to Q75 was melted previously, replaced coil. Coils have proper voltages, aux pwr board coil diodes are good, TIP36Cs for slings are good. Switches tested ok. Fuse values are correct everywhere. I figured all was well.

    But when in test mode, activating Q75 via pop switch causes it to violently fail, take out pre-driver + U45 7402. It seemed almost delayed, whereas I didn't see it coming to shut the game off immediately. All other special solenoids did not activate either, minus the right sling. Q75 was the last switch tested and it blew up and I had to replace the driver, pre-driver and U45 again.

    With IJ18 & 19 disconnected, everything else is fine. I have barakandI's solenoid saver on the way before I test again.

    Any ideas where to inspect next? PIAs? I've usually seen this the other way around where coils just lock at pwr on, and replacing upstream logic + drivers takes care of it.

    #2 9 days ago

    i just realised i left the coil mounted diode on the replacement....yeah, that would do it.

    Leaving this post in hopes it helps someone else to not overlook.

    #3 6 days ago

    not so fast

    got andrew's sss board to test SS section again, all working now except Q75 pop. Trigger that pop, locks on. Turn off game, turn on, locks on now. Unplug IJ18, still locking, so not a switch issue. Time to replace upstream U49 and retest U45 to see if it shorted it out again. But at least no blown TIP102 again. SSS board fuse did not blow. Didnt want to leave engaged long enough to test that though.

    #4 6 days ago

    U45 isn't shorted, but I've got three blown TIP102s with the inline driver fuses in place. Q73, Q75, Q77. 3 pops. Getting closer.

    Any ideas why it cascade failed like that and why fuses didn't pop? I must have some streams crossed somewhere.

    Going to replace U50 & U49 now.

    #5 6 days ago

    had the sss board upside down, which explains why the fuse didn't pop.... sucks having limited time, lots of mistakes.

    #6 5 days ago

    uggghhh... Q75 keeps blowing. SSS fuse not popping. No clue. But TIP102s did not cascade fail, but tested that way in circuit after the Q75 short with 1J19 connected prior to socketing U50 & U49, so good clue there, like if a diode shorted.

    Seems like something is connected wrong, but I've checked a dozen times now it feels like. Unless a PIA can do this sorta thing. Or another component failed now that was working previously. Going to recheck zeners. Aux pwr diodes are fine.

    #7 5 days ago

    Replaced Q75 again. All other SS circuit components tested out again on the game. Everything checks ok, pre-drivers fine, drive transistors fine, Logic is good, Zeners all giving around 5k resistance, resistors compare fine to others, values all look the same. On a whim, I replaced the diodes on the aux pwr board again for the pops, but they tested fine out of the game.

    With MPU in game, J118 & 19 disconnected, logic levels look right from U49 buffer to U45 & U50 lines on the NOR gate like it should to provide GND path when in test mode. Holds high outside of test or game mode, so nothing is getting stuck. PIA isn't negatively interacting anywhere from what I can tell.

    Replaced SR19 since some of the readings were below 4.7k, but it tested fine outside. I've got my Swords of Fury MPU to A/B things now, because at this point, I'll never figure this out otherwise. But it really seems like it isn't board related. Coils all test fine, 4 ohms on all 3 pops, 14ohms on slings. Swithces test fine, no shorting between the score & activation switch, or mounting screws/pop body, etc.

    Last time when I was at this point and plugged in 1J18 & 19, I got all the SS components working fine with repeated tests, with the exception of Q75 Pop, which fired about 3-4 times normally when triggered, then fried the Q75 and locked on again. So whatever it is that is causing it to fail after replacing the drive transistor, it takes a few times before the transistor breaks down. It definitely is failing like if you had a shorted coil diode.

    Could I have created a current sink somewhere when it had that explosive failure initiallly? I have Leon's test rom to check PIAs if it really did travel that far upstream.

    #8 5 days ago

    Time to test without a coil in a safe environment.
    You can connect an LED or bulb in series with a resistor so that Q75 won't fry.

    If it then works without blowing Q75, something is wrong with diode (D17 ?) on the aux-board.

    #9 5 days ago

    Good idea. I'll throw an LED in line with a resistor and eliminate that coil from the equation and see if Q75 still blows. Divide and conquer is definitely the way to troubleshoot at this point.

    #10 2 days ago

    I replaced the diodes for the pops on the aux board again for good measure. I'm about to replace all of them in the lower coil voltage path at this point, even though they tested fine. Also replaced the pre-driver for Q75. Put sockets in place for Q75 & the pre-driver. It isn't ideal for long term, but for now, it will help if I have to keep replacing Q75. I also tried swapping coils with another.

    Still blowing Q75. Pops 4 times, then blows out the collector side consistently. I'm going to swap power & gnd return wires with one of the other pops. After that, I guess it is time for Leon's test at this point, as every other logic IC involved tests fine.

    I don't have a high wattage resistor at the right value on hand to do the LED test, unless there is some other way to kludge it together. The only 1+ watt resistors I have are either too low a value or too high. I think I need something in the 2k-5k range at 1 watt or higher to do that, right?

    #11 2 days ago

    If you want to hook up a 6V bulb (in place of the coil) it would be a resistor of about 200 Ohm / 5 Watt.
    For an LED in full power setup, a 10K 1/4W resistor would work. And possible a diode in blocking direction across the LED.

    But in a test setup without (!) coil power, the lightbulb can be powered by the 5V without resistor. For the LED an 1K will do.

    #12 2 days ago

    Thanks zaza, that clarifies things for tests. I was thinking of high power, and you were talking about probing +5v with an LED to see if it is stuck on I'm assuming. I had done probes with my meter previously to rule out all those logic IC areas. I'm going to focus on PIAs later tonight.

    #13 1 day ago

    It has to be something on the aux pwr board, I've gone through everything at this point. MPU is fine. Leon test shows the PIAs are fine. Checked logic switching with an LED test and it doesn't lock on. Even took apart the entire pop. I still don't know why the solenoid saver board isn't popping fuses. Going to replace every single 1n400x diode on that board next here.

    #14 1 day ago

    Unfortunately the LED test is not like a real solenoid. The LED should be considered a resistive load. The solenoid is an inductive load. This gave me a lot of grief when I was trying to figure out what was wrong on the first revision of my WPC-89 power board. It passed on the bench 100% every single time yet when I put it in a machine it ALWAYS failed - resistive versus inductive load. I had the added grief that I went to the trouble of constructing an inductive load on the bench but the problem still did not manifest.

    I would suggest taking the trigger switch out as a possible cause. Disconnect 1J18 and keep it disconnected. Then enter diagnostics and keep the coil test set to the problematic solenoid and let it run repeatedly. If it does not fail then somehow the trigger switch is related. The goal is to isolate as many parts of the circuit as possible and to test, test and test.

    Failing all of that ... sometimes posting pictures of your board or wiring / connections can sometimes shed some light.

    EDIT: You can also put an explicit diode across the problematic solenoid (at the solenoid) if you think it's a back EMF problem. Be sure to put the banded end on the power supply wire.

    #15 1 day ago

    Thanks for the ideas DA. I will throw a diode on that coil as an additional EMF protection to rule out the Aux board for now. I'm leaning that way, since it consistently blows after 3-4 switch actuations. Make sense that would be some sort of blowback threshold for the TIP102 breakdown. I'll also disconnect 1J18 and let it rip in test mode and see what happens. I don't care about blowing TIP102s now that I have sockets in place. It has made it less painful to test ideas. Sometimes getting over the fear of blowing things up is 1/2 the battle.

    When I was doing logic probing, I did disconnect 1J18 and stuck an LED+Resistor to watch the logic, triggering the pop switch over and over, let it sit, came back, repeated. Unfortunately I didn't catch it misbehaving at all or latching on any of the NOR inputs or the output.

    What kills me about this is that is that it seems brain dead, whatever is going on. I'm like 8 hrs into debugging this now. It is isolated to the one area, so it should be easy to debug. I've got to be glossing over something dumb. No AH HA moments yet though.

    #16 21 hours ago

    With switch removed & diode running across the coil, Q75 does not blow!!! (in cpu activated test)

    #17 21 hours ago

    So the issue is the switch path. Locked on with switch activation when I reconnected it and burnt up Q75.
    Going to replace the zeners now and inspect any other parts I haven't replaced yet in that switch path. I've only got 6.8v zeners on hand, but I'm guessing that is fine, since they're supposed to function as dumps for overvoltage anyway.

    So that rules out everything else. Thanks again DA.

    #18 20 hours ago

    Replaced zeners. Still locking on with the switch and killing Q75. I honestly have no clue what to do at this point. I checked U45 again and it looks fine.. Same with SR20. Stuck my meter on the switch again and tested that out a bunch to see if it was a physical issue, but it checked out fine. The only part in that switch path I haven't replaced is C71 .1uf cap.

    #19 19 hours ago

    The switch trigger path also includes the playfield components not just the board components.

    #20 12 hours ago

    Someone doing a Taxi restore noted that they had an issue with the capacitor on the pop switches being internally shorted which caused a locking on. Couldn’t hurt to check there.

    #21 11 hours ago

    Unfortunately, i've replaced all parts on the switch, short of the leaf switches themselves. But it has to be the switch, otherwise Q75 would blow with CPU controlled test.
    I'll replace C71 on the mpu for shits, and ill swap out the solenoid switch itself.
    The red flag here is that the inline fuse for coil power to Q75 does not pop.
    What would cause the TIP102 to short only with switch activation, and NOT also blow an inline fuse?

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