(Topic ID: 253073)

SYS 11C Alphanumeric Display Digit Issue

By crazi

12 days ago

Topic Stats

  • 13 posts
  • 5 Pinsiders participating
  • Latest reply 9 days ago by Quench
  • No one calls this topic a favorite


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    #1 12 days ago

    Hi All

    So on "BOTH" displays digit 5&6 13&14 are both dead when I turn the machine on.

    After about 20 seconds digit 6&14 on BOTH displays is up working, bright and crisp.
    After about 90 seconds digit 5&13 on BOTH displays is up working, bright and crisp.

    As this is happening exactly the same on both displays I don't believe the issue is the display glass. It must be coming from a shared/common point most likely on the MPU.


    1J1/4 - Strobe 5 - both Displays
    1J1/3 - Strobe 6 - both Displays
    1J2/4 - Strobe 13 - both Displays
    1J2/3 - Strobe 14 - both Displays

    So I replaced U44 no difference and then U51 on the MPU but again no difference.

    The resistor arrays on the MPU SRC 7, 8 & 9 all measure ok.

    I have checked the cable/header connections and all seem fine.

    Once it's working you have to leave it off 3 or 4 hours or overnight before you get the issue again.

    Thoughts? What am I missing?

    #2 12 days ago

    Just to add U41 on the MPU has also been replaced. It was faulty as a faulty Left display was blowing U41 as soon as you turned the game on. I fixed that display U1 & U2 and replaced U41 and the game booted fine. Just this weird digit issue now...

    PSU HV are 102 & -102 so all good.

    #3 12 days ago

    sounds like a cold solder joint. I know you checked them, but just reflow them all, that's pretty much part of the reliability equation for newly acquired machines.

    #4 12 days ago

    I did reflow them already. Including the SRC's just in case

    I have just put the Left display in my Dr Dude and it came up straight away so I'm certain it's not the displays...

    It's very much like a dry joint symptom though. Or bad header cable connection type thing but all checked re/done re/soldered...

    #5 12 days ago

    Any corrosion damage?

    #6 12 days ago

    No the board is pretty good

    #7 12 days ago

    Any caps involved?

    #8 11 days ago

    none on the diagram. Not around U44 or U51. Just the resistor arrays.

    It's doing my head in

    #9 11 days ago

    Do you have a logic probe?

    #10 11 days ago

    Have a scope... the problem is you have to find the issue within 60 to 90 seconds and if not then leave it off for a few hours before trying again

    I just swapped Dr Dude MPU and everything was good so what ever the issue is, is definitely on the MPU.

    I have just soldered the component side of the SRA's and re-soldered U44 "applicable pins"

    Issue still there (although strobe 6/14 seems a bit better but might be my imagination) 5/13 still dead for 60 odd seconds

    #11 10 days ago

    So I connected CH1 of the scope to 1J2-2 (strobe 15 which is good) and CH2 of the scope to 1J2-4 (strobe 13 which is dodgy). Left it off a few hours and then turned on. Both channels got a square wave immediately and now and again move but move in sync with each other.

    So that makes me think the issue is not the output of U44 or the PA side of U51 (U44 inputs).

    U51 PB side also goes to 1J3 connector. I don't know what this is doing though.

    A1 A2
    B1 B2
    C1 C2
    D1 D2

    What are these outputs driving on the displays????

    As far as I can see it is also segments but on the right display only. Which if correct I can't see that being the issue as the entire digit/strobe is dead for 60 seconds and then starts (warming up) and works great after circa 90 seconds and it is only the 4 strobes not all 16...and the issue is on the left display as well..

    so U44 & U51 seem great yet these are the two IC's controlling the stobes... AAAARRRRGGGGG

    #12 10 days ago


    #13 9 days ago

    crazi you might get better support if you move this thread to the alphanumeric tech subforum:


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