I have two different JPACs that I am struggling to get working properly.  My problems relate to the controls.  The video sync part on both of them are working just fine.  I know one of the JPACs worked perfectly in my Dynamo cab that was wired for JAMMA when I got it.  The inputs and everything worked just fine.  
Fast forward to now and I have my Donkey Kong build that I wired up for JAMMA myself and a friends cabinet that I also wired up for JAMMA.  I can not get the button inputs to work on either of these.  The keyboard passthrough works just fine, but I get no input from the JAMMA harness OR the extra button ports.  
I have the same exact problem on both cabs, which I wired.  I can only assume I have something wired wrong on the JAMMA harness to work correctly for the JPAC.  I can plug a JAMMA PCB into the JAMMA harness and the buttons work just fine on both cabs, plug in the JPAC and I get nothing.  I have checked my grounds and they all check out.  The only thing I can think is that I need to ground the JAMMA harness to the cab in a certain way other than I have it now.  It is driving me nuts.  I would assume the JPACS are both bad in some way but one of them works fine on my other DYNAMO cab that I did not wire. 
Any ideas?