Printronix L1024, Maintenance Manual

Page: 129 / 372

7–33 Chapter 7 – Fuser Subsystem
3. Measure the resistance across the terminals on the lamp side of the cable (C and D). It
should measure less than 2
Ω
(less than 6
Ω
for 220 VAC units). If not, remove the heat
shield cover and measure across the thermal breaker (A and B). It should measure near 0
Ω
.
If the thermal breaker measures near 0
Ω
, then check the lamp. Measuring across B and D should
result in less than 2
Ω
(less than 6
Ω
for 220 VAC units). If not, then replace the lamp.
CAUTION: Use extreme care in handling both the old and new lamps, as the
lamps are extremely fragile. Also, avoid getting fingerprints on the
new lamp as this will shorten its life. If you get fingerprints on the
lamp, wipe the lamp with a soft cloth soaked with alcohol. Allow the
lamp to dry completely before powering on the printer.
If the thermal breaker is open (
∞
Ω
), replace it.
CAUTION: If you replace the thermal breaker, you must check the operation of
the heat sensing circuit (thermistor and Low Voltage Power Supply).
Otherwise, you might be merely correcting symptoms caused by a
more serious problem, rather than correcting the more serious
problem.
4. If both the lamp and thermal breaker check OK, reinstall the heat shield cover. Then defeat
the cover interlock switch, the paper empty switch, and the top-of-form switch. Connect the
printer power cord to the power outlet, turn on the printer, and check the voltage at S211
(CNS1).
WARNING: When you defeat the cover interlock switch, there is 115 VAC at
various parts of the power supply and high voltage at other
contacts—so BE VERY CAREFUL.
Be sure that all cables and test leads are out of the way of any moving parts (gear train, tractor, etc.).
At this point, 115 VAC should
not be present at the output of S211 (CNS1). If 115 VAC is present, you
should suspect a faulty thermal breaker, one that is intermittent. It is unlikely that the lamp is faulty,
since lamp faults usually are visible (broken tungsten wire or cracked glass envelope).
5. If 115 VAC is
not present at S211 (CNS1), then turn off the printer and disconnect its power
cord. Remove the bottom cover from the printer. Disconnect the 2 connectors CN1 and CN2
on the Low Voltage Power Supply.
See Figure 7–7 on page 7–34.
Check the main power fuse F1 (6.3 amp, 250 VAC), then check fuse F3 (15 amp, 125 VAC). This is
the fuse that protects the output. If this fuse is good, check the input of the power supply at CN2–16
(the HEAT signal). To check this, you will have to very carefully replace the power cord to the printer.
You will also need to defeat the cover interlock switches as per Step 4 above.
WARNING: When you replace the power cord, there is 115 VAC at various parts of
the power supply so BE VERY CAREFUL.
Using either a voltmeter or a logic probe, monitor pin 16 of CN2. When you turn the power back on,
the printer should pause for a few seconds and then try to heat the fuser. At this point, the HEAT
signal should go from
≈
+5.0 VDC to
≈
+0.7 VDC. If the voltage changes from high to low and you still
do not have 115 VAC at CN4, then replace the Low Voltage Power Supply.