I know this thread is a bit old, but I thought I'd chime in on my experience yesterday.
I just bought a Triple Dollars game with a 16mhz board that had the low battery code 12. I replaced the battery, and then had the same issue as the Kingpin - a 61 that would clear for a second, then come right back. I had a clear chip for my other S Plus game with a 10mhz board, and decided to try the chip in the new game. The clear chip worked! After swapping the game chip back in the game fired right up.
That's good because you had a clear chip to erase and reset the CMOS & motherboard chips.
The problem here was is that Kingpin did NOT have a IVC0123 Clear chip to use.
Sometimes you can drop in a totally different SP chip and
that will force the MPU to do a partial clear.
Then you throw back in the original SP chip and the  error code
will clear to [61-1] after pressing the test button.
From there of course, you you close the door
and turn the reset key to boot into the game mode.
Another way is to remove the CMOS chip and ground the legs of the
device onto some flat metal to totally corrupt the chip.
Then re-install the CMOS back into the U51 socket and you can sometimes be back in business!
If you're fortunate to have a 6-pin socket installed on the motherboard at the U1 location -
you can also replace that C024 chip with a new blank eprom to get the machine to initialize.