(Topic ID: 274716)

Buzzing Flipper Relay

By oldschoolbob

3 years ago


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    PIA_PortB_Pins.gif
    SDB_Flipper_Schem (resized).png
    SDB_Flipper_Schematic.gif
    SDB_Coil_Drive_Voltages.gif
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    #1 3 years ago

    I just finished rebuilding a MPU and tested it in my Meteor game. I played about two balls and heard a buzzing in the backbox and the flippers stopped working. I turned it off and checked the backbox. Everything looked OK so I turned it back on. It booted fine and no buzzing. I started a game and it started buzzing again. Sounds like the buzzing is coming from the relay. It was getting late so I turned it off and came upstairs.

    I’ve never seen a bad relay before. Is that sound like a bad relay to you?

    Thanks

    Bob

    #2 3 years ago

    Check the two power traces at the point where they reach the flipper relay coil solder pads. I've had two or so solenoid driver boards where one of those traces had fractured at that point causing intermittent connection driving the relay.

    #3 3 years ago

    Thanks Quench, I had some shop time today and worked on the driver board. I may have misunderstood what you called power traces. I checked the traces from the relay to J1 and J2. They looked fine and showed less than 1 ohm resistance. I re-soldered the connections anyway. Then I replaced the crimp connectors. I played one game and it worked fine. Second game it buzzed again.

    What I didn't check was the traces going to the transistor Q15. I'll go back tomorrow and check that trace. There is also a diode (CR20) in that circuit. Could that be bad?

    Thanks for the help. We'll beat this.

    Bob

    IMG_5214 (resized).JPGIMG_5214 (resized).JPG
    #4 3 years ago
    Quoted from oldschoolbob:

    I may have misunderstood what you called power traces.

    Pins 7 and 8 are the power pins for the coil in the relay. I don't see any cracking on the traces from your picture.

    Quoted from oldschoolbob:

    There is also a diode (CR20) in that circuit. Could that be bad?

    No. CR20 is just a diode across the relay coil - it's there for same purpose as the diodes you see on playfield solenoid coils.

    When the problem next occurs, measure the voltage on both sides of diode CR20. The banded side should measure 43 volts, the non banded side should measure near zero volts. Since the diode is across the relay coil, it'll help isolate where the issue is.

    #5 3 years ago

    The board is back on the bench. I checked out the power circuit (7 and 8). It looks fine and the continuity is good back to Q15. I haven't checked the components in that circuit yet. Do you think any of those could cause this problem? How about a bad crimp connector?

    I'll check voltage when I get it back in the game.

    Thanks

    Bob

    #6 3 years ago
    Quoted from oldschoolbob:

    Do you think any of those could cause this problem?

    If I had to guess, diode CR15 would be my first suspect but you're unlikely to detect it on the bench. Diagnosing this in game during failure would be my approach.

    #7 3 years ago

    Check voltage like before on each side? What should I read?

    Bob

    #8 3 years ago

    Are 1 and 3 supposed to be bridged together?
    They look it in the pic.
    -Mike

    #9 3 years ago
    Quoted from oldschoolbob:

    Check voltage like before on each side? What should I read?

    Black meter lead on ground, red meter lead on each side of CR20. Only reason for measuring at CR20 is it gives you front of the board access to the power pins of the relay. CR20 itself is not of interest.

    Quoted from Grizlyrig:

    Are 1 and 3 supposed to be bridged together?

    They're not supposed to be bridged. Worth checking.

    #10 3 years ago

    The photo above was before I cleaned the rosin from soldering. There was no bridging - but good catch.

    IMG_5220 (resized).JPGIMG_5220 (resized).JPG

    I gave another close look at the traces and they all look fine. Also checked with the ohm meter - less than 1 ohm all the way to Q15. Also checked Q15. All checks good.

    You can almost see the trace on the other side down to the Via.

    IMG_5221 (resized).JPGIMG_5221 (resized).JPG

    If I get time I'll put the board back in and check voltages.

    Thanks for the help.

    IMG_5225a (resized).jpgIMG_5225a (resized).jpgIMG_5227a (resized).jpgIMG_5227a (resized).jpgIMG_5229a (resized).jpgIMG_5229a (resized).jpg
    #11 3 years ago

    It just gets stranger. I had a spare driver board - it checked OK a year ago. I put it in the game but now I have no flippers.

    I have 47 volts on both sides of CR20.

    Recap:

    The games was working fine.
    I changed MPU's to see if the rebuilt one works.
    The flipper relay starts buzzing.
    I changed driver boards now I have no flippers.

    Seems like the more I do the worse it gets. Ever have one of those days?

    I think I'll go upstairs before I loose general lighting.

    Bob

    #12 3 years ago
    Quoted from oldschoolbob:

    I have 47 volts on both sides of CR20.

    The Blue-White wire from MPU J4 pin 7 to SDB J4 pin 8 controls the flipper enable relay. You probably have a bad connection on either end likely the SDB side.

    #13 3 years ago

    Those connectors are new - but it wouldn't be the first time I messed up a connector.

    I thought about changing that crimp connector when I changed the other flipper connectors on J1 and J2. I must be getting lazy.

    Would a loose connector cause the buzzing problem?

    Thanks

    Bob

    1 week later
    #14 3 years ago

    I had a little shop time tonight. I changed SDB J4 pin 8. ( didn't change MPU J4 pin 7 yet). I now have no buzzing but no flippers. I checked both sides of CR20 and get 48 volts on both sides.

    I checked the schematics and MPU J4 pin 7 goes to R103 - SDB J4 pin 8 goes to R37. I checked continuity between those two and it buzzed out OK. So I think the connectors are fine.

    The MPU in the game is the one I rebuilt and the SDB is my backup board. Next I'll try the original boards.

    What would happen if I ground the tab on Q15?

    Thanks

    Bob

    #15 3 years ago
    Quoted from oldschoolbob:

    What would happen if I ground the tab on Q15?

    Grounding the metal tab of Q15 should activate the flipper relay.

    If you hook up a wire to ground and insert the other end into J4 pin 8 at the solenoid driver board, it should also engage the flipper relay. If not you have an issue in the drive circuitry on the solenoid driver board.

    #16 3 years ago
    Quoted from Quench:

    If you hook up a wire to ground and insert the other end into J4 pin 8 at the solenoid driver board, it should also engage the flipper relay. If not you have an issue in the drive circuitry on the solenoid driver board.

    Would hooking a jumper from ground to SDB R37 do the same thing? That would be a lot easier.

    Thanks

    Bob

    #17 3 years ago
    Quoted from oldschoolbob:

    Would hooking a jumper from ground to SDB R37 do the same thing?

    Yes, provided you jumper to the R37 leg that connects directly to J4 pin 8. The other leg of R37 is connected to 5V, so no room for error.

    1 week later
    #18 3 years ago

    FINALLY - I get back to pinball. First I had the replacement SDB (Stern) in the game. No flippers. When I ground the tab on Q15 the flipper relay clicks and I have flippers - as long as the tab is grounded. Not grounded = no flippers.

    Then I put in the original SDB (Bally) and I start a game. Flippers worked for about 3 balls then I get the buzzing relay. When I ground the tab the buzzing stopped and I have flippers for about one minute. Then it starts buzzing again. Repeated this several times - same thing.

    Could I have two messed up SDBs?

    Bob

    #19 3 years ago

    The MPU board has a signal specific for enabling the flippers. It comes from MPU U11 pin 16 and out on MPU J4 pin 7 to the SDB at J4 pin 8. It's a Blue-White wire according to the Meteor schematics.

    When that signal is High, the flippers are disabled (relay is OFF).
    In this state, the high signal coming out of MPU U11 pin 16, downstream results in pin 3 of U4 on the SDB to come up to around 0.9 volts. U4 is just a transistor array (it contains 7 internal transistors).

    When U4 base pin 3 is 0.9 volts, it results in the collector pin at U4 pin 2 to drop to around 0.3 volts. U4 pin 2 connects to the non-banded leg of diode CR15 and when U4 pin 2 is around 0.3 volts, no voltage is passing through diode CR15.
    This results in the base leg of driver transistor Q15 to be at 0 volts from the pull-down resistor R39 which switches the Q15 transistor OFF at the collector leg (metal tab) and so the flipper relay coil doesn't engage.

    When MPU U11 pin 16 goes low to enable the flippers, downstream it results in SDB U4 pin 3 to drop to around 0.3 volts which releases the U4 pin 3 collector leg that's connected to the non-banded side of diode CR15. The voltage here rises to around 2.1 volts. The non-banded side of diode CR15 going to the base leg of driver transistor Q15 rises to around 1.4 volts which switches ON transistor Q15 so the collector leg (metal tab) connected to the relay gets switched to ground placing 43 volts across the flipper relay coil that engages it.

    See the voltages in the chart below. Confirm your game is roughly in these ranges when it's working. When it's not and the flipper relay is buzzing, look for any abnormal voltage change.

    SDB_Coil_Drive_Voltages.gifSDB_Coil_Drive_Voltages.gif

    SDB_Flipper_Schematic.gifSDB_Flipper_Schematic.gif

    #20 3 years ago

    Great explanation. I copied your post and put it in my pinball folder. I've always wondered how this circuit worked.

    Today I have no flippers and no buzzing.

    First I checked voltage in attract mode (flippers off):
    U4-3 = 0.89
    U4-2 = 0.4
    CR15 non-banded = 0.41
    CR15 banded= 22mv
    Q15 tab = 46.9

    Then I started a game (but now I have no flippers):
    U4-3 = 0.82
    U4-2 = 1.37
    CR15 non-banded = 1.37
    CR15 banded = 0.8
    Q15 tab = 34 to 35 V not steady.

    Why would U4-2 jump from 0.4 to 1.37 ? I would expect it to be the same as flippers off.

    When I ground the Q15 tab the relay clicks in and I have flippers. When I disconnect the ground the relay buzzes for a short time then stops. No flippers after it stops.

    I haven't checked U11 pin 16 yet.

    #21 3 years ago

    I just tried again This time the flippers came on.

    U4-3 = 22mv
    U4=2 = 5 mv
    CR15 non band = 16 mv
    CR15 band = 25 mv
    Tab = 2 mv

    Flippers were still working so I tried again:
    U4-3 = 15 mv
    U4-2 = 22 mv
    CR15 non band = 33 mv
    CR 15 band = 43 mv
    Tab = 50 mv

    I played with the flippers for a minute or so while they worked then I heard something score and the flippers stopped. (no ball in play so noting should score). I couldn't hear any buzzing. Then I checked the voltages again:
    U4-3 = 22 mv
    U4-2 = 26 mv
    CR 15 non band = 31 mv
    CR 15 band = 34 mv
    Tab = 30 - 40 mv.

    When it comes to MV most of the voltages fluctuate a lot.

    None of these voltages make any sence to me.

    Thanks

    Bob

    #22 3 years ago
    Quoted from oldschoolbob:

    Why would U4-2 jump from 0.4 to 1.37 ? I would expect it to be the same as flippers off.

    That almost sounds like the Q15 driver transistor is the wrong type. It looks original from your pictures, but just confirm it's the same type transistor as the others.

    What happens when you connect a jumper wire from test point TP6 on the SDB to the banded side of diode CR15?
    Note test point TP6 is there specifically to allow you to manually switch driver transistors ON with a jumper wire to test the driver transistor.
    When you do this, measure the voltage on TP6. It should be around 1.5V from memory.

    Your voltage readings on U4 in the previous post (post #21) don't make sense. Are you sure the meter leads were making good contact?
    When U4 pin 3 ("base" pin of the internal U4 transistor) is getting near zero volts from the MPU board, the collector pin of the U4 internal transistor on pin 2 should get pulled up to around 2.1volts thanks to the 120 ohm R38 pull-up resistor - note CR15/Q15 limits it from going higher.
    Check that R38 resistor is around 120 ohms to make sure it's in spec.

    #23 3 years ago

    I checked the Q15 - it's the same as the others that have not been changed. While I had the board out I changed Q15 and CR15 anyway. I also checked R38 = 119.3 ohms.

    I put the board back in and started a game. No flippers. I then rebooted and while still in attract mode I checked U11 pin 16 = 1.813v. I started a game and U11 pin 16 read 0.656 v.

    Without turning it off I checked the SDB (it was in game play mode but still no flippers):
    U4 - 3 = 0.82
    U4 - 2 = 1.43
    CR15 non band = 1.41
    CR15 band = 0.79
    Tab = 38.6

    Then I rebooted and checked again while in attract mode:
    U4 - 3 = 0.88
    U4 - 2 = 0.42
    CR15 non band = 0.42 (now here is the strange thing - While doing todays checks, I would check the voltage, record my reading, then check again to be sure. After writing down the voltage I re-checked CR15 non band - is was now reading 1.2mv. The next two voltages were after the 1.2mv reading)
    CR15 band = 5.4mv
    Tab = 47

    I turned it off and took a little break. Then came back and checked TP6 - it read 5 volts. Then I connected a jumper from TP6 to the banded side of CR15. The relay kicked in and the voltage read 1.37.

    Looking back I wish I would have went back and checked U11 after the reading of 1.2 mv at CR15. Do you think U11 is going bad after it warms up?

    Thanks

    Bob

    #24 3 years ago
    Quoted from oldschoolbob:

    I put the board back in and started a game. No flippers. I then rebooted and while still in attract mode I checked U11 pin 16 = 1.813v. I started a game and U11 pin 16 read 0.656 v.

    That output voltage on pin 16 of U11 is not low enough when in game mode - it's not switching off the SDB U4 transistor to enable the flipper relay.
    Swap the MPU board U10 and U11 6821 PIA chips around.
    U10 actually gets software configured to use pin 16 as an input, not an output. So that suspect chip currently in U11 will probably work perfectly fine in U10.

    #25 3 years ago

    Thanks Quench,

    I'll get on that tomorrow. (wife went to bed).

    Would U11 cause the drop from 0.42 to 1.2 mv at U4?

    Bob

    #26 3 years ago
    Quoted from oldschoolbob:

    Would U11 cause the drop from 0.42 to 1.2 mv at U4?

    Yes.
    Below is the SDB schematic of the flipper circuit with the noise removed. I've also expanded what Q15 really is - it's known as a darlington transistor which actually contains two transistors in one that gives very high current gain - needed in this circuit for switching.

    When about 0.55 volts is presented to the base leg (pin 3) of the U4 transistor, it begins to conduct a small amount of current from the collector leg to the emitter leg (pin 2 to 15 respectively). The more you raise the voltage (current) on the base leg pin 3, the more current the transistor conducts from collector to emitter. We are talking only a difference of about 0.25 volts variance on the base pin 3 between the U4 transistor barely conducting all the way to fully conducting.
    The base leg (pin 3) of U4 will never go above 0.9 volts. If you do measure it above this then the U4 transistor is faulty.

    SDB_Flipper_Schem (resized).pngSDB_Flipper_Schem (resized).png

    #27 3 years ago

    I think we got it. I replaced U11 and played about 4-5 games. I left the game on and took a short break. When I came back I played 5 -6 more games and it worked great. Looks like U11 was the problem. I got a bunch of PIAs from China a while back and I think this was one of them. It worked fine for a while but just didn't last very long. I see GPE now has PIA's from Western Design (not China). Has anyone used them yet?

    Now all I have to do is put everything back together again.

    Thanks Quench for all your help and great explanations.

    Bob

    #28 3 years ago
    Quoted from oldschoolbob:

    I see GPE now has PIA's from Western Design

    I think I've seen pinsiders using them.

    Below is the internal schematic of the 6821 port B pin of which one of them drives that flipper enable signal.
    The MOSFET transistor I've circled in red is what pulls the output pin to zero volts when it needs to go low. That transistor is likely going weak in that chip.

    When the chip is configured for the Port B pin to be in input mode, you can see the signal takes the blue path and that output transistor is not used.
    That chip should work fine in U10 which configures that pin for input mode.

    PIA_PortB_Pins.gifPIA_PortB_Pins.gif

    1 year later
    #29 2 years ago

    I just had a similar problem on my Playboy (relay buzzing & losing flippers) turned out replacing the U11 (not an AMI brand) fixed it.

    I had the relay buzzing, the coin door lock out coil buzzing & all the displays showing garbage. As I had all 3 issues simultaneously, I turned to the MPU & U11.

    The pins were heavily tarnished which may have been the problem - might clean them up & refit later to check rather than throw out in case that's all it was.

    #30 2 years ago
    Quoted from Joydivision:

    turned out replacing the U11 (not an AMI brand) fixed it.

    The pins were heavily tarnished which may have been the problem

    Fairchild 6821? Their pins tarnish pretty badly.

    #31 2 years ago
    Quoted from Quench:

    Fairchild 6821? Their pins tarnish pretty badly.

    Yep, spot on a Fairchild - looks like the Fairchild 6820s tarnish badly as well.

    A leg just broke off... it's the end for this chip after 43 years service!
    IMG_0223 (resized).JPGIMG_0223 (resized).JPGIMG_0227 (resized).JPGIMG_0227 (resized).JPG

    #32 2 years ago
    Quoted from Joydivision:

    A leg just broke off...

    Weird, in the middle of the stubby section too.
    Repairable with a cut leg from a faulty chip if you're game:

    IMG_0056a.jpgIMG_0056a.jpg

    #33 2 years ago
    Quoted from Quench:

    Weird, in the middle of the stubby section too.
    Repairable with a cut leg from a faulty chip if you're game:

    Yeah, I have done that before, especially with 2716/2532 eproms which I want to definitely reuse. - good as new. I will probably repair & retest that chip as I am curious to see if it was the tarnishing or a failed chip as the culprit.

    It was weird it just broke at that wider point - I hadn't bent it there.

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