Understanding photosensor failure modes
PS112 is a photosensor actuated by a flag.
Photosensors have two failure modes. The
photosensor is made up of two components, a
light emitting diode and a receptor. If the diode
fails, it behaves like the flag is engaged; the
light path is always occluded. If the receptor
fails, it behaves like the flag is never engaged;
the light path is always open.
Failure modes
Receptor fails
Actuating the flag has no effect on the device.
The control panel will typically display
MISMATCH PAPER SIZE FROM TRAY N and
41.3 UNEXPECTED PAPER SIZE errors when
Letter/A4 or Legal media is processed from any
tray where paper size is indicated. Media will
feed from Tray 1 without this messaging when
paper size is set to Any. If media narrower than
7.4 inches transits the MFP without error, but
wider media (Letter/A4) causes the error
message, it is likely that the PS112 photosensor
has failed.
Corner case (rarely seen)
The device may not wake up and/or may
display PROCESSING JOB indefinitely. If the
photosensor flag PS112 is faulty, the MFP may
power up to READY but, when you attempt to
perform a copy or print job, the MFP may hang
in a PROCESSING JOB state indefinitely. In
another scenario, if the printer goes into Sleep
Mode with the failed sensor, the device may not
come out of Sleep Mode. A change to the DC
Controller firmware was implemented in version
17 to correct these problems, but the behavior
is ultimately caused by a faulty PS112 sensor
which should be replaced to resolve the issue.
The DC Controller should not be replaced.
To verify a PS112 failure, perform the following
test:
1. Turn the MFP off.
2. Remove the toner cartridge and tape down
the PS112 flag found under the registration
assembly jam access flap. Reinstall the
toner cartridge.
3. Power the MFP back on. The device should
display 13.20 JAM IN TOP COVER AREA
REMOVE PRINT CARTRIDGE. If it displays
READY the sensor PS112 is faulty.
Diode fails
• The device will power up and display 13.20
JAM IN TOP COVER AREA REMOVE PRINT
CARTRIDGE. No paper is found in the paper
path under the toner cartridge.
1. Make sure there isn’t a scrap of paper stuck
in the sensor flag and that the flag moves
freely. Look for toner dumping in this area.
If toner builds up in the flag slot it is
possible it may partially occlude the
photosensor.
2. Execute a Paper Path Sensor test. Make
sure all sensors are active, moving from 0
to 1 as the media transits the paper path.
3. If all paper path sensors check out OK, the
media width sensor PS112 is defective.
Solution or workaround
The page width sensor PS112 is part of the
central printer block. This part is not
replaceable. If the PS112 fails the entire printer
must be replaced.
Note
We have seen instances where the PS112
sensor fails because of toner buildup in the
sensor. In the cases we have investigated, this
is due to toner dumping caused by
remanufactured toner cartridges. We have had
success resolving the failure by blowing out the
sensor using compressed air.
HP LaserJet MFP updates 15
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