Lexmark 4039-1XX - Manual (Page 34)

20 Service Manual
4039-1XX
Fuser Theory
The fuser lamp operates off line voltage from the LVPS. The
thermistor is in contact with the fuser hot roll. The system board
reads the thermistor resistance and toggles a TRIAC in the LVPS
which cycles the lamp on and off to maintain the proper hot roll
temperature. Inside the fuser shroud there is a thermal fuse which is
in series with the lamp; if the TRIAC fails and leaves the lamp on
continuously, the fuse melts and shuts off power to the lamp.
The thermistor output voltage is proportional to the fuser
temperature and is on (10P/10R/12R/12C/12L) J19-6 (16L) J16-6.
The voltage will cycle from approximately 2.0 to 2.3VDC as the lamp
goes on and off during idle, and will be around 2.7VDC during
continuous printing when the Fuser Temperature is set to Normal. In
Power Saver mode the lamp is left off until a job is printed.
The system board signal to the LVPS TRIAC is on (10P)J11-16
(10R/12R/12C/12L) J11-3 (16L) J18-16. The voltage is 0VDC when
the lamp is to be on and +24VDC (10P: +5VDC) when the lamp is to
be off. The lamp can be tested by briefly connecting this pin to
ground.
Fuser: 920, 921, or 922 Error
A 922 error during a POR caused by low line voltage can usually be
cleared by doing another POR.
If the fuser lamp is lighting very dimly, check for a 220V lamp
installed in a 110V machine.
Check all the connectors to the exit sensor card and the lamp power
connections at the left end of the fuser. Make sure the thermistor is
making contact with the hot roll. Check the continuity of the lamp, the
thermal fuse, and the fuser power cable. Check the thermistor
resistance at (10P/10R/12R/12C/12L) J19-5 to J19-6 (16L) J16-5 to
J16-6; it should be from 100K Ohms to 260K Ohms when cold; it
may be as low as 2.3K Ohms when hot but increases quickly as the
fuser cools. There should be no connection from either pin to
ground.