Quoted from Pinballjimmy:I know there are plenty of posts about this but I'll tell how this happened and what I've done troubleshooting.
This started with having an weak left flipper. It would make shots but when the ball lands on it coming from the left loop the flipper would bounce down slightly and bounce back. Sometimes when the ball is travelling especially fast would cause the flipper to collapse. While holding the flipper button down I could push the flipper down with one hand. Then the flipper would act as if it only had the hold power until I released and pressed in again the flipper button.
I rebuilt the flippers; full kit, EOS switch properly gapped, new sleeves, new bat bearings. Everything new but coils. This did improve snappiness but the weak issue remained.
I went into test mode and the EOS switches register properly. I swapped sides on the flipper buttons and nothing changed. I pulled the wiring from the flipper coils and ran alligator wires from the left wires to the right coil and this made the right flipper behave weak just as the left side had been. I ran alligator wires from the right flipper wiring the the left flipper coil and it was strong. I put everything back the way it should be.
From this I feel I had felt I eliminated in the cabinet and there was a problem on the board. From this assumption I pulled the board and replaced Q15 with a transistor IRL540N. Put the board back in and the flipper was immediately strong as it should be. It was just as strong as the one on the right. However it immediately blew the resistor because the flipper would not go back down after I let the button go. It would drop back down when I opened the coin door so its not a mechanical bind.
At this point I replaced the diode on the coil ensuring I did not reverse it. I replaced the transistor again. I buzzed out the legs on the new transistor to the proper points on the board and there is continuity. Turned on game. Flipper is strong but again immediately blew the transistor. Flipper locking up when the coin door is closed.
The flipper coils are the 090-5020-20T. Left resistance is 3.2 ohms. Right is 3.4 ohms. I've triple checked and wiring to the coils is correct. I did not reverse anything pulling and replacing the wires to the coil lugs.
Side note, the original transistor I pulled was not the original transistor to the game as there was evidence it had been replaced.
Was the original one that seemed weak an IRF540 instead of IRL540?
Double check the coil wiring and diode polarity is consistent with other coils. Make sure the diode on the coil is truly in circuit. Make sure you get IRL540 from an authorized distributor. Power mosfets highly faked. Seems common that they take a weenier Chinese transistor like nce0117 and mark it as a IRL540 which cannot take the abuse of the flipper coil.
IRL540 should be the preferred part. Stern had issue for a little while where if someone held a flipper button down a long time it would kill the original specified mosfet that could handle less current than IRL540. IRF540 may not fully turn on all the way. It seems to work in some boards but is weak in others.
Fort Lauderdale, FL
