Printronix L1024, Maintenance Manual

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7–31 Chapter 7 – Fuser Subsystem
7.4.4 Troubleshooting
To properly troubleshoot the fuser section, mentally separate the assembly into four functional sections:
S
Heater and heat safety section (thermal breaker)
S
Temperature control section (thermistor)
S
Paper positioning section
S
Fuser section
Troubleshooting procedures for each of these four functional sections follow.
Fuser Heater and Thermal Breaker
The fuser heater is a quartz halogen lamp that has a rating of 1000 watts. The heater safety device is a
one-shot normally-closed thermal breaker that has a trip point of 155
°
C. This thermal breaker ensures
that the printer (not necessarily the fuser) is not damaged if the temperature control does not function
correctly. If the thermal breaker senses an over-temperature condition, it will open and remove power
from the heater lamp.
During initial power up and during any warmup period, there is a signal generated in the engine controller
called HEAT. This signal is generated by monitoring the TMRSG line returning from the thermistor.
When the controller decides that it is time to heat the fuser, it generates a low on the HEAT line. This
signal leaves the controller via J8–8 on the Backplane Board. This TTL signal controls a solid-state relay
(TRIAC) in the Low Voltage Power Supply which gates 115 volts out of the supply on pins CN4–1 and
CN4–2. (If the Low Voltage Power Supply is set for 230 volts, it gates 230 volts out CN4–1 and CN4–3.)
This voltage, in turn, goes to the lamp and thermal breaker, which are wired in series.
If the Fuser Lamp Does Not Heat:
1. Allow the printer cool down to ambient temperature and unplug the printer from the power
outlet.
2. Open the printer and remove the cover that fits around the drive gear assembly. Locate S211
(CNS1), the output from the Low Voltage Power Supply to the fuser lamp, and unplug the
fuser lamp connector from it.
See Figure 7–5.