There is no reason you can't get a drop target bank in there to replace stand ups.
You need two things to happen.. Have the machine read the state of the target switches and have a way to drive the reset coil.
In this thread I am going to show you how I have managed to get fully functioning drop targets installed in my machines and how I drive the reset. It does depend on my Total Lightshow board for driving, so it's not a completely stand alone method that just allows you to buy a target bank and jam it in there and away-you-go, but I don't think anyone expects that could happen easily anyway.
I will break the install into two parts. 1 - Installing the bank and hooking up the switch matrix cables and, 2 - Hooking up the power and driver to the coil. Then I will briefly cover the creating of the drive signal.
I am going to start here now with the way I connected things using stuff I already had or could get easily, and later I will do it with the custom connector boards I have designed that neatly connect the switches as well as the power.
What you will need..
A drop target bank, available from distributors or Pinball Life or Marco, etc.
A Stern 50V step up board.
Crimps and stuff.
1 - Installing the drop bank.
I have started with the TNT targets in my AC/DC Pro VE. First thing to do is remove and desolder the stand ups. This is really easy. Just undo the mounting screws, drop them out and touch a soldering iron to the wire tabs and the wires simply drop off. They should come off as a joined pair. There are two ends coming into the solder joint and you want them to stay together.
Tape off two of the drive wires. You only need one. They are all the same wire. You will now have one only drive wire and then one return wire for each switch.
Install a crimp on each of these exposed wires.
Insert into an appropriate crimp housing. Making sure you keep the return wires in the same order. You don't want to mix up the targets.
Place the target bank against the playfield underside and line up the targets so they move correctly through the gap. Mark the holes, then remove the bank and drill pilot holes. Here, you will have to consider how the insert lamps may have to mount with the new frame in place. This will be different for every machine. In the TNT case, two of the three went straight back in and the third just required a little jiggling.
Screw in the target bank. Make sure the targets are height adjusted and that they move freely through the gap and that they manually reset properly.
Plug in the switch matrix plug that you made.
Now you need to bring 5V to the target bank. You can get this anywhere. I used the square molex connector in the backbox in this case, but you could use the cabinet aux 5V, and I also have 5V sources on the TLS board.
2 - Powering and driving the reset coil.
You need 50VDC, ground and 20VDC. I pushed into the unused pin 8 on J10 for the 50V. I put a 3A fuse in F7, which is a lower rating than the factory 4A and is the same as the fuse used in the other coil circuit. I pushed into pin 2 on the same connector for the ground.
20V I got from the flasher circuit. I built a piggyback cable so the flasher can just be unplugged, my cable plugged in, and the flasher replaced, and I now have 20V. This 20V goes to the 50V step up board to tell it that it's ok to generally operate. It's not used in the actual firing.
Now I have to make up the connector that is going to plug into the step up board. The 50V, GND, and 20V all come to this connector. The 50V continues through to the coil along with a coil ground. The coil ground only goes from the step up board to the coil. Crimp and house the coil wires so they can plug into the connector that comes on the target assembly.
The last wire that has to come to this plug is the drive signal used to fire the coil. This line needs to be sunk to ground to fire the coil. In this instance I have run this line into an isolator and then into the ground braid in the machine cabinet. I will use my TLS board to drive the gate on the isolator.
Here is the isolator knocked up on some veroboard. Signal and ground for the gate go back to the TLS board, one of the load pins goes back to the IN line on the step up and the other to the ground braid.
Mount the 50V step up board somewhere near your target bank.
Plug the connector into the board.
Plug the coil connector into the coil.
That's all the install and connecting done. Just now take the isolator signal back to the appropriate output of the TLS Matrix Interceptor and that will send the signals for firing the coil.
Sending the firing signal.
You could do this in whatever way you want. I already have my way to do it, but someone could come up with a neat way to trigger the gate signal from another source. The install and wiring above is independent of what you want to use to send the reset signal, and will work on any SAM machine.
For those unfamiliar with Total Lightshow, very quickly, its main board, the Matrix Interceptor, reads the states of all insert lamps and switches in the machine, so I use a combination of the TNT target switch states and the TNT insert behaviour, plus new ball and new game events, to determine when to send a coil fire pulse. I use a 40ms pulse which seems to be a standard pulse length for drop resets.
That's it. The TNT drop targets are fully functioning and now the connecting just needs to be cleaned up. I am doing away with the wire running to the ground braid with a very neat little board that sits on that step up header before you plug in the harness, and I have a connector board that plugs into the back of the target assembly PCB to attach the switch wires through screw terminals rather than having to crimp. When those boards arrive I will redo that part of the installation and put the new pics up.