Stuck coin switch on Simpsons pcb

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Well, as part of progress on my Simpsons restoration I knew I'd have to deal with player 2's coin input being stuck closed according to the test screen. I know this is a board failure because it does this in any cabinet or test rig. JoshBrown80 and I took a look at the schematics tonight and we are 99% certain we have narrowed it down to the SN74LS257AN chip which handles the coin inputs. Pin 6 is player 2's coin and when I test from that pin to ground, it's shorted. No other pins on that chip short to ground except ground of course so it seems like this chip has to be the problem. I have a junk 6 player X-Men pcb that has a similar chip SN74LS257BN. The difference being the Simpsons chip has an A and the X-Men board has a B as the second to last letter. Can anyone tell me if these are compatible or if I need to find the exact one as on Simpsons. If anyone also cares to verify that Josh and I are correct with our diagnosis that would be great too.

Here's the manual with a schematic for anyone that cares to look.
http://arcarc.xmission.com/PDF_Arcade_Manuals_and_Schematics/Simpsons.pdf
 
Stuck Coin

The 74LS257A and 74LS257B are completely interchangeable. Have you looked at both sides of the board closely to make sure there is nothing causing your short? Are you sure it is not the chip before it? I would suggest lifting the lead on one or the other to verify before changing anything.
 
Stuck Coin

I forgot to mention that the 005273 looks like a resistor array but is actually a custom chip for Konami. That is the 'other' chip I was referring to above. It is marked S31 pin 3 to U21 pin 6. It would be easiest to lift the pin on U21 to verify.
 
Thanks for the replies. So that custom 5273, if bad, could cause pin 6 of that 74LS series chip to show a short?

Edit: Also we did a visual inspection of the board with no signs of problems. We did test that custom 5273 as a resistor thinking it was a resistor pack. From the in and out points the resistance was all showing as the same. Since it's not actually a resistor pack, I'm guessing that test is a moot point but I thought I'd mention it. That chip was my first suspect before we really dug into the schematics to test things.
 
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Yeah! 2 chips 1 line = either chip can be bad. lift the pin on one and check or if you are pretty sure it is the 74ls then change it out. They are cheap.
 
Is there a decoupling cap on that input? I've come across boards where there's a decoupling cap to ground in parallel with the pull-up resistor. If the cap fails it'l short the input to ground.
 
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