After replacing a flipper MOSFET (Q15 left, Q16 right) the flipper is very weak, bounces back when hit, or the previous replacement soon failed and locked the flipper on.
Whitestar flipper weak or dead after a MOSFET swap: fake part, test with TPL1
Cause: The replacement P20N10L was a remarked counterfeit that needed about 4.2 V on its gate to turn on, so the board's logic-level drive could not switch it fully.
Checks
- Use test point TPL1 (labelled FET), which puts 3.4 V on a MOSFET gate: jumper TPL1 to the white-banded end of R1-R16 to fire Q1-Q16. A coil that doesn't fire points at that MOSFET. TPL2 does the same for the TIP transistors Q17-Q32 via their resistors.
- Look for sanding marks, square tabs and odd dimensions on suspect parts.
Fix
- Fit a genuine logic-level MOSFET (an IRL540 was used) from a reputable source and retest with TPL1.
Board-level work; unplug the game and keep the jumper only on the named test point and resistor.
Systems
Related tips
- Magnet driver MOSFETs on Last Action Hero and Guns N' Roses
- Last Action Hero / Guns N' Roses: magnet dead or locked on
- Spare MosFETs for the driver boards
- Logic-level MOSFET equivalents: 12N10L, 20N10L, 22NE10L, IRL530, IRL540
- Guns N' Roses: magnets blow their 2.5 A fuse in multiball
- One flipper flips but has a weak hold and drops when hit: bad transistor at Q16
- Resets when the flippers are used: arcing flipper coil, then bridge rectifier BR21
- Whitestar: I/O board blanking LED flashes, lamp rows 1 and 3 dead: data bus short
Source: Pinball Repair help group!! (Facebook group)