How many pings do you hear when the game boots up? It sounds like you may have shorted 43v supply into the switch matrix and damaged the switch PIA (and possibly other components) on the MPU.

You should NEVER use metal tools inside a game while it's turn on for this exact reason. To add credits, simply use your finger to actuate the microswitch in the coin chute. You can also set max credits to 40 and the replay threshold as low as it will go and very, very rarely will you actually need to add credits to the game.

PIA is the peripheral interface adapter chip and it interfaces the switches in the game with the microprocessor.

I am fairly certain you do not have a problem with your displays nor your feature lamps but rather your MPU simply isn't booting because the PIA is fried. The ping sounds you hear are the MPU going through a self-diagnostic procedure. There should be 7 in total. How many do you hear?

I'm not sure if Alltek's boot procedure is the same as the original MPU's, but a missing 7th flash on the oringal indicates a fault in the zero cross circuit which is usually caused by missing 43V. Check to make sure fuse F4 on the rectifier board is good and that you have 43V at the MPU test point. You may have simply shorted the 43V supply to ground and blown the fuse which is far less catastrophic than shorting 43V to the MPU!

That's good news! Sounds like you probably just shorted 43V to ground. Replace that fuse and see if the machine boots.

For troubleshooting purposes, you could temporarily substitute a fuse of a lower value just to see if the game boots. The only load on the 43V supply during boot is the flipper relay and the coin lockout, then the drop target reset coils one at a time. Should be able to go as low as 1A without blowing the fuse. You obviously won't be able to play the game, but it will let you know if you're heading in the right direction.

To test the transformer inputs like this, the game needs to be turned on and F6 installed and working.

Agreed. Something is causing the line fuse to blow and you need to ensure the supply from the wall outlet all the way to the transformer is sound.

I'd also recommend unplugging J1 and J3 from the rectifier board while you're figuring out the line fuse issue. This will disconnect everything in the backbox and the playfield and will ensure components downstream don't get damaged or adversely affect your voltage readings on the rectifier board. Just be very careful - with these connectors removed the game will appear "off" even when the mains switch is on.

Just curious, is the rectifier board original? Have the connectors been replaced?

Try removing J1 and J3 from the rectifier board, replace the fuse, and power on. J4 still blow? If so, replace the bridge rectifier. If it doesn't blow, the problem is likely elsewhere in the game.

Nice work! That board is not an easy one to replace.