The anti-ghosting LED's are just a workaround to the root problem. They effectively delay the time it takes for the LED to turn on, so that the small spikes which incorrectly turn the LED's on at the wrong time are filtered out.
The problem (on games using a lamp matrix) is mostly a software timing one (excluding the WPC ASIC bug) then the game code needs to be changed to allow time for one column transistor to actually fully turn off, before turning on the next one. So having a short think about that, I can't imagine a simple hardware solution to this software bug (or at least certainly not one that can be plugged into the outputs of the column/row drives of a driver board)
The WPC bug makes things worse, as a simplified version of what is happening is :- When the CPU is attempting to read lamp rows (i.e. see what the current values are) the ASIC incorrectly assumes that the CPU is trying to write values and ends up turning on all of the lamp rows for a very brief period.
As a bulb is quite slow to turn on, the pulse of current has already gone away before the bulb filament has warmed up enough to emit light.
As an LED turns on almost instantly, you see every single one of these little tiny spikes as the ASIC is turning on all the rows every few microseconds.
A simplified version of what the patched ROM's (for WPC games) does is :- A value is written to the lamp rows to turn them all off, before the read occurs, thus when the ASIC incorrectly picks up the read, the values are already set to off, so the asic doesnt incorrectly turn them on. The patch also has a side effect in that in adds a delay between one column turning off and the next one turning so in theory giving the previous transistor enough time to fully turn off before the next one comes on.
@Carl Spiby - Your original question about using resistors is a red herring, as the resistor fix is for old Bally games (amongst others) that use SCRs to controll the bulbs. An SCR needs a minimum amount of current draw for it to "latch" on. When you use an LED in an old Bally game, the LED comes on, but the SCR does not latch, so it goes back out again until the game tries to turn it on again, hence you get a constant flashing on the LED's that are suposed to be lit up steady. The resistor in parallel to the LED simply increases the current draw (by burning off some power as heat) and thus allows the SCR to properly latch on.
