Quoted from UNCCShannon:I guess this might be a good time to ask but can these be wired backwards? especially when there is no diode present? When I searched there seemed to be mixed answers and unfortunately I cannot find the wiring schematic for the playfield unless I am overlooking it, all I find on ipdb is the schematics for the boards and solenoids, etc. Anyways I figured I would reach out to the community as you all are always extremely helpful. Thanks in advance!
welcome to Taxi club...
Fun basic pinball facts:
-All coils have voltage at all coil lugs at all times (when measured with the cabinet rail as GND). I know, I know it's hard to believe but it's true 99.9% of the time in pinball.
-A coil is just a piece of coated magnet wire wrapped around a plastic spool. This is why you see voltage measured at all coil lugs, at all times.
-A diode's job is to allow current to only flow in one direction. This is really only important in regards to pinball coils because each coil has a ground wire, as well as a power wire (the GND wire is usually smaller gauge). This confuses people because the ground wire isn't for supplying power (until it's needed). The ground wire essentially does nothing until the game's MPU tells a pin on one of the PIA pins to register, that in turn then goes to a small IC, then to a small pre-drive transistor, then to a main drive transistor (usually a tip102), then to that GND wire that touches the coil and it FIRES. This all happens in a fraction of a second. The diode is there to isolate this violent spike of power, not allowing it to flow in the other direction, potentially killing sensative electronic components. It is all about isolating the high 20-40V coil voltage from the sensative 5V components being used. All if this is what makes solid state pinball possible.
-Taxi (and all the other system 11B and 11C games) are odd because they do not have diodes at the coils... but THEY DO STILL USES DIODES! The pinball designers simply moved the diodes to the "AUX driver board" in the head so that you can't screw up what lug the GND side touches with the bands of the diode (either anode or cathode). That is, not unless you install the diode backwards on the AUX board! The diodes in a game with an AUX board are also much more robust than that diodes previously used in pinball.
-If you are following along here, you should now be able to tell if it matters what wire goes on what lug on a TAXI coil with no diodes.
-Diodes are also used for isolation on switches and lamps in pinball machines. If not for them, there would be a LOT MORE WIRES needed. It's all about efficiency and isolation.