We have a Sharp MX-B401 that has been coding out with an L4-12. We have followed Sharp bulletin TT-20213 and checked for proper operation of the shutter on the resist sensor unit, replaced the primary transfer belt unit, secondary transfer roller unit, fuser unit and both gears in the engine that drives the fuser unit.
The drum unit and developer units have also been replaced.
Still codes out with L4-12 during use.
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