OK quick calculation
Grabbed an old Bally coil
352 ohm hold coil
43v powered
I = V/R
43v / 352o = 0.122A
or 122ma current
and in watts thats
P = IV
43v x 0.122 = 5.2W power
Unfortunately there are no data sheets for pinball coils that I am aware of, so we can't calculate the temperature rise of the coil dissipating 5 watts, as we would need the thermal resistance to ambient value.
As it is a large package, I am going to have a total guess at 7c/w, so that would give a guessed temperature rise over ambient of 36.4c
At 25C ambient, the coil would hold indefinitely at 61.4c
Your average cheap enamel wire has an insulation rating of 130/150c, so your old solid state pinball machine literally does not care about you holding the flippers for as long as you want. I would need to work out the temp rise on a coil at a fixed current to verify that though.
What would be interesting however, would be if I would stop acting like a man, and read the manual for my scope, I could use some of the built in advanced math functions to actually work out the power dissipation of a SAM or Spike flipper coil under PWM hold and how it compares to old solid state flippers.
There is still an even more simple explanation for all this, it could be fake Chinese MOSFETs with a smaller than required die size. These are in such common circulation, it would not be infeasible for Stern to have bought a load.
If anyone ever has a flipper MOSFET fail It would be interesting to remove the other still working one, and give it a proper load test on my bench with a DC load and known current to check if it is real and meeting specs.
Hopefully everyone is not rolling their eyes at me right now and hopefully I am not the only person that finds things like this interesting
