Ok, this might get long, but i want to completely explain my issue. I have a Joker Poker that i purchased 18 months ago. It wasn't working. It came with a NiWumph CPU and Driver Board, and Rottendog Power Supply installed. Also Rottendog Driver and original CPU and Driver not installed. I was able to get it working after sending the board back to Niwumph and changing the interconnect and fixing some other small issues. I took it to PATZ last year and on the first day, theAces Drops quit working and then the kings locked on and burnt the coil. Upon further inspection i found a number of oversized fuses installed (i know i should have checked them previously). So i replaced the coil, and sent the driver board back to Niwumph and it was repaired again. It has worked fine for the past year with very sparse use. I took it to PATZ again this year and on Sometime Thursday night the Aces quit again. It had worked fine for most of the day. I found the fuse blown. When i went to replace, the coil locked on. So on Friday i took the original Driver board (that i had never done anything to) and installed it to see if it would even work. It worked great. Then sometime Friday afternoon/evening i found the game turned off, so i turned it on and the aces would try to reset but wouldn't go up far enough to "latch". if i raised the PF, the would reset when on a horizontal plane. i talked with some of the experts there and they had me check the coil voltage and i was getting about 15 volts that my meter could catch, and the other coils i was getting 20. So that is why it wouldn't go all the way up. I had emailed Ace at Niwumph to see what he remembered fixing and this is what he sent me:
"If I recall correctly, it had a blown transistor, and it was replaced – though that doesn’t help you that much. I am going to assume that the FET is blown again. If the problem is light use versus heavy use, then I can guess that the problem is going to be a playfield coil diode. These FETs are great for a game, but crappy when it comes to reverse bias, and that only happens with the coil fires, and then shuts off, once the diode is damaged. My guess, is that there is a problem diode somewhere in the game, it may even be the ACES bank you mentioned, and that this is damaging the FET. The fact that it is not happening right away would mean that the reverse voltage is not that bad, so the diode might NOT be the ACES bank."
So today, i checked the transistor on the Niwumph board and it seems to be bad. I also checked the MPS-U45 and the 2N3055 Q29 and Q45 on the original board.. They both seemed to check out as good. So my question is does Aces' recommendation sound probable, also if the original driver transistors check out ok, why was i losing voltage and where? I also checked the aces coil and it measured good. I did perform the recommended ground mods to the cpu and power supply, i didn't add any ground mods to either driver board. Any thoughts?? Sorry for the novel...

I was originally using the Niwumph driver. I had planned on doing the ground mod to the original gottlieb one after I ended up installing it, until I could get the niwumph repaired. I was just hoping to get through the rest of the show. I will replace the coil diodes and check for splashes. it just seemed weird that the original board seems to be ok when I test it, but quit working in the game. I have done all the recommended mods as far as I remember, I will double check. I will also do the ground mod on my Niwumph. I just have to figure out where to add the ground, as my board is different than the one in the Wiki. Mine is a 2007 and doesn't have the "H2" location.

I do know that Niwumph MPU does not work with Rottendog Driver board. It is a know problem. The boards, for some reason, do not like each other...
I will do the mods on the original board either way.

could be, i know Niwumph told me it wouldn't, and didn't when i tried it, and i was doing some internet checking and found a few sources that said the same thing. So hopefully like you said something was updated somewhere.

This is from the Niwumph web site: " Please note; Ni-Wumpf CPU's do not work with Rottendog driver boards - there is a component incompatibility with the chips on that product. If you are having issues with the tilt or game-over lamps, this is the most likely source of the problem."