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Thread: Shorted Matrix Row That Won't Unshort.

  1. #1

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    Shorted Matrix Row That Won't Unshort.

    One of those, it will probably be this but no, well it's more than likely this but no, well I'll change this piece because there isn't much else to change but no. I'm now to the point of what the fuk is causing this?.

    Here's the rundown. It's a Judge Dredd coming up with "Gnd Short Row 2".

    I take out all the matrix cables, problem still there so it's a board issue.

    Changed U18 and put in a socket. Problem still there.

    Probed all pins on the chip to there destinations on the board for continuity, all checked fine.

    Checked all associated resistors and caps, all checked out fine.

    Changed U13 and put a socket in. problem sill there.

    Checked continuity between J208/209 pin 2 to D4, fine, checked between R53 to U18 pin 9, fine, checked U18 pin 14 to R 29, fine. R29 to U13 pin 13, fine. Checked Gnd and +5v on U 18, fine. Checked U13 D6 to U12 and D14 D6, fine.

    Checked R 29 5volt, fine. Checked 12v to U 18 pin 3 fine. Checked 12v R54, fine.

    Changed R54, 53 and R29 even though they were all within specs. Changed C4.

    Well that is what I am up to and still have "Gnd Short Row 2" coming up. What have I missed?. I was going to pull the ASIC but I figure if the problem was on D6 (pin 27) or Switch Row (pin 48) on the ASIC, there will be more than just one row not working correctly.

    I'm open to suggestions on this one. Not much I pull the pin on but this one is getting there. I am simply running out of parts to check or change.

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    Had similar prob once. ended up being faulty ribbon cable between cpu and driver board


    Sent from my iPhone using Aussie Arcade
    Wanted funhouse and taxi pinballs.

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    Quote Originally Posted by Autosteve View Post
    One of those, it will probably be this but no, well it's more than likely this but no, well I'll change this piece because there isn't much else to change but no. I'm now to the point of what the fuk is causing this?.

    Here's the rundown. It's a Judge Dredd coming up with "Gnd Short Row 2".

    I take out all the matrix cables, problem still there so it's a board issue.

    Changed U18 and put in a socket. Problem still there.

    Probed all pins on the chip to there destinations on the board for continuity, all checked fine.

    Checked all associated resistors and caps, all checked out fine.

    Changed U13 and put a socket in. problem sill there.

    Checked continuity between J208/209 pin 2 to D4, fine, checked between R53 to U18 pin 9, fine, checked U18 pin 14 to R 29, fine. R29 to U13 pin 13, fine. Checked Gnd and +5v on U 18, fine. Checked U13 D6 to U12 and D14 D6, fine.

    Checked R 29 5volt, fine. Checked 12v to U 18 pin 3 fine. Checked 12v R54, fine.

    Changed R54, 53 and R29 even though they were all within specs. Changed C4.

    Well that is what I am up to and still have "Gnd Short Row 2" coming up. What have I missed?. I was going to pull the ASIC but I figure if the problem was on D6 (pin 27) or Switch Row (pin 48) on the ASIC, there will be more than just one row not working correctly.

    I'm open to suggestions on this one. Not much I pull the pin on but this one is getting there. I am simply running out of parts to check or change.


    So you haven't checked U20 and U14?

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    Quote Originally Posted by Boots View Post
    So you haven't checked U20 and U14?
    No because it is a Switch Row 2 ground short and I wouldn't have thought U20 or U14 would affect the row as both these chips seem to be only Column related but I may be wrong.

    This is the diagram I use for repairing WPC MPUs. It's a '89' board but pretty close.



    You can use this diagram and see exactly what I have checked so far.

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    Quote Originally Posted by Jaybee View Post
    Had similar prob once. ended up being faulty ribbon cable between cpu and driver board


    Sent from my iPhone using Aussie Arcade
    I didn't have a spare to check with but was able to turn around the existing one, problem still there.

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    ULN2803A how many would you like I have heaps.
    My pins: Wild life EM, Top Score Em, Space Mission EM, Target Alpha EM, Cleopatra SS, Pin*Bot SS, Indiana Jones WPC, Black~Rose WPC.
    My Arcades: Funland Rifle EM, Hankin Table 20", Mame 20" Horizontal Cab, 17 in 1 Horizontal 20" cab, Outrun2 sit down game rear projection, Foosball table.


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    Nice picture ^^^

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    Quote Originally Posted by Gemini2544 View Post
    ULN2803A how many would you like I have heaps.
    You think U20 as well?

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    Quote Originally Posted by Autosteve View Post
    You think U20 as well?
    U20 is a Darlington array I.C and is responsible for the switch matrix control. I would replace U20 first as it's a $2 chip & it should be socketed as they regularly fail. This chip has a history of failing partially on rows, columns or a single x,y position without affecting other matrix functions.
    My pins: Wild life EM, Top Score Em, Space Mission EM, Target Alpha EM, Cleopatra SS, Pin*Bot SS, Indiana Jones WPC, Black~Rose WPC.
    My Arcades: Funland Rifle EM, Hankin Table 20", Mame 20" Horizontal Cab, 17 in 1 Horizontal 20" cab, Outrun2 sit down game rear projection, Foosball table.


  10. #10

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    Quote Originally Posted by Gemini2544 View Post
    U20 is a Darlington array I.C and is responsible for the switch matrix control. I would replace U20 first as it's a $2 chip & should be socketed. This chip has a history of failing partially on rows without affecting other matrix functions.
    Arr OK. I've changed a fair few U20 ULN2803 in the past but they have always been to fix switch Column problems. This is actually the first switch Row shorted to ground problem I have had and couldn't see how U20 would effect a whole Row to become shorted.

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