Flipper power and reaction is certainly directly linked to the mechanical condition of the mechanism regardless of age of machine and design, mechanical or otherwise. If the machine is more than a few years old chances are the flippers need some sort of attention even if only new sleeves.
The OP is also asking about new or near new machines and the flipper power. This question is directly related to the electronic design of new Stern machines flipper system. It started with DE machines and has been problematic ever since. Why they have stuck with it is anyones guess?
Put simply the flipper coil is switched by a MOSFET. The EOS switch has nothing to do with the current flowing through the coil - it simply tells the CPU what position the mechanism is in.
At flipper button press, the MOSFET is switched on (or pulsed depending on the operator setting in software to determine flipper power) and the coil pulls in - the micro looks for a closure of the EOS within a certain time frame and if it sees it the coil power is reduced by rapidly switching the MOSFET on and off THROUGH THE SAME COIL. If the EOS closure IS NOT seen in the allocated time the micro "assumes" the mechanism has made it and that the EOS switch is faulty and switches to low power regardless.
All of this jiggery pokery creates a very complex set of currents flowing through the coil and without a doubt creates a lot of heat in the coil and huge switching currents in the driver MOSFET (which is known to fail frequently - why that is a surprise I have no idea, it shouldn't be).
The failure of these driver transistors is well known and it comes as no surprise to me that they fail. I can't see how any engineer with any idea of the "real world" could ever have thought this was a good idea in the first place. This is the sort of mad design you see university graduates that don't know which end of a soldering iron to hold come up with.
I am NOT having a go at Stern, far from it. I do think it is long overdue for them to get a "real" electronic engineer on the job however and get rid of this stupid idea - enough is enough IMO!
