Bally 5500 error code 24

[pepsikid64]

I have a Bally 5500 that has an error code 24, COIN REVERSE. This comes up right after start up. I do a safe ram clear and it comes back. I don't drop any coins, the code just comes up on its own. I have a second 5500 that works and I swapped parts like coin competitor and optic board. No Help
I just got this machine, it wasn't working due to a dead CPU battery. Replaced the battery and got this code. Need a little help with this one. Thanks

[Sunrise Side]

Try reseating the harness connections at the door and backplane

[pepsikid64]

I thought we had something.  When I was resetting the connectors I checked the CPU connectors and found pin C21 bent. So I straightened it out and put everything back together. When I powered it up the code came back. So I  did a partial SafeRAM clear. I restarted the machine and the code still comes back. I did notice that the Coin optics board and Comparitor leds aren't lighting up like my other machine.

[Sunrise Side]

Try swapping your power supply

[pepsikid64]

I was able to get some life back in the machine tonight. I did a complete SafeRam clear and restarted the machine with the optic board from the good machine,  code game back. Did another Ram clear, restarted with the connector off the coin optic board. The fault did not come back. I was able to feed in some paper money and it gave credits.  Played just fine. Maybe the harness for the optic board has a open or a short.