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problem with Mp chassis


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  • problem with Mp chassis

    I've one 9800 chassis that developed a no spot problem, I'm stumped!
    The chassis runs the respot cycle fine, on second ball the sweep goes to guard, sweeps through, table goes to pick up pins for respot. Changed chassis, problem followed. Changed board, problem followed. Changed S relay, problem stayed. C-1 is clean and in good shape. Sweep and table relays are 5-6 months new.
    Any help is appreciated

  • #2
    You said you replaced the S relay and it made no difference. The S relay controls the sweep and since you indicated the sweep was running I wouldn't suspect the S relay as an issue so I would expect changing it would make no difference.

    You also said you swapped the chassis and the problem followed which is good because it tells us the problem is likely in the chassis or the connector. Further you said you swapped only the board and the problem followed the board meaning the rest of the chassis is likely good. This would eliminate most of the chassis components and leave us to focus on the board itself. Can I assume you put a good board in the questionable chassis to make sure the chassis functions properly with a known good board in it? As well as putting the questionable board in a good chassis you need to put a good board in the questionable chassis to make sure the chassis will work fine with a good board in it. HOWEVER, you need to be careful doing this. There is a varistor across the spot relay to control inductive spiking. If this varistor shorts out, it can cause a dead short to ground which could be what caused the problem in the first place. If that's the case, putting a good board in this chassis could damage a second board. Usually, this will cause the CB to trip but not always. Just something to be aware of. You can check this by checking the resistance across the coil of the spot relay. If you have a lower than normal resistance, you may have a bad varistor.

    Instead of the S relay, you need to look at the spotting relay. When the relay is off, the normally closed contacts route power to the respot solenoid. If the relay is not energizing, then the respot solenoid will be active by default. This will cause the detect stroke after the sweep clears the deck like you described. Since you indicated the problem followed the board we can probably assume the spot relay is good, just not getting power.

    If this is the case, then look at the spot relay with the bad board in the chassis. If the spot relay is not energising then you probably have a bad triac on the board. Then with a good board in the chassis, look at the spot relay again. If it now energises, then it's a board issue. If you are comfortable repairing these you can repair it yourself (after further diagnostics of course) or you can send it in for repair. Just confirm it is the board first by putting a good board in the bad chassis to make sure it resolves the issue.


    • #3
      I meant to say the problem followed the chassis. Swapped board with adjacent lane and the problem stayed with the original problem child. Sorry, long night...

      I might not be using the correct terminology, are you referring to the ice cube 11 pin relays when you say spotting relay? The book says SP and S is stamped on the plate. I'll try to be on the same page with everyone.


      • #4
        So, I'm slightly confused. Are you saying when you swapped the board, the problem stayed with the chassis and the board worked fine in another chassis? Just trying to verify. If the board worked fine in another chassis, then it's probably the relay rather than the board. Check it the same way I discussed above. You are looking at the same general issue just maybe a different cause.

        Also, below is a pic of the relays list for the 9800 from the service manual just for your reference.
        Attached Files


        • #5
          I got pulled away with another job...

          exMech, correct, the problem stayed with the chassis and the board tested good on adjacent machine. I did swap boards with adjacent lane then swapped back with no issues with either board. Now that leaves me to test the varistor, correct? I did change the spot relay with a knowingly good relay, with no change. I'll be on this hopefully for the next 2 days before Thanksgiving break.

          Happy Thanksgiving to all,


          • #6
            Hey Lee. Yep, I would check that Varistor. They sure like to cause problems.


            • #7
              I have attached a pic of the spotting relay circuit. As you can see, this is a fairly simple circuit so it shouldn't be to bad tracking down the problem.

              The T1 secondary leaves the chassis via C2A-22 and connects to terminal C on the circuit breaker. It then ties to ground through the circuit breaker. So with the power off and the machine unplugged, take and ohm meter and check the circuit. To do this, remove the spot relay from the socket. Then take the ohm meter and measure the resistance from terminal 2 on the socket for the relay to ground. I don't recall how much resistance you should get but it should be a fairly low reading. You will have some resistance do to the transformer and CB coils. You can do the same thing to a known good machine if you want to know what you should be reading. If the reading from terminal 2 on the socket to ground is within an acceptable range, then you know the wiring from that side of the socket is good. This will include the C2A plug so you can eliminate that.

              If you can't get your meter probe into the socket, you can put a stick pin, wire or something into the socket to make the connection. Just don't get to big a piece as it is possible to stretch the connector and cause a bad connection for the relay. If you don't know which terminal is number 2, you should be able to tell which terminals the relay coils are from looking at the relay. Then you can test both of the sockets for the relay and one of them should give you the readings you are looking for while the other will give you very high ohms.

              The other test involves removing the card and probing at the board connector. Terminal 10 from the socket goes to the pc board where the circuit is grounded. You can remove the card and measure the resistance from socket terminal 10 to 228-3 on the P-2 connector. In this case, you should get 0 ohms resistance. Again, if you don't know which is terminal 2 and which is terminal 10, check them both and one should give you the desired result. For reference, I have included a layout of the connector. Also see the note on how to read the connector scheme.

              If you want to, you can measure between terminal 2 and terminal 10 of the socket. Do this with the board out. This will tell you if the varistor is shorted. If it is good you should get a high reading. If it is shorted, you should get a low reading.

              This should tell you if the problem is between the relay and the transformer or the relay and the board. If these appear to be ok you can power the machine back up and with the relay still removed. measure the voltage from terminal 2 of the relay socket and ground. You should get around 23 VAC. If you don't get this then you may have a bad transformer.

              Post back and let us know what you find out.
              Attached Files


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