Tektronix Phaser 840, Service Manual

Page: 94 / 207

Service Guide 83
6.
Perform the front panel Clean cycle Eliminate Light Stripes and check the
PEAK vacuum and DECAY time to determine if there is a problem with the
vacuum system (pump, solenoid valve or tubing) or cap/wipe/purge
assembly gasket.
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Normal operation.
In normal operation, the vacuum builds up a inside
the vacuum module. At the moment the solenoid valve opens (you
should hear a “click” as the valve opens), the PEAK vacuum of about
50 cm Hg (20 in Hg, 10 psi) +/- 10% is applied to the printhead faceplate
(and the vacuum gauge). Immediately, the vacuum should then drop to
25 cm Hg (10 in Hg, 5 psi) +/- 10%. The vacuum should then bleed off to
0 with a DECAY time of 4 to 6 seconds.
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Low peak vacuum. If the PEAK vacuum is less than 36 cm Hg (14.2 in.
Hg, 7 psi), check the vacuum at vacuum module without the T-
connector. Disconnect the vacuum module’s tubing and connect the
vacuum gauge directly to the module. If PEAK vacuum is less than
40 cm Hg (15.7 in. Hg, 7.7 psi) replace the vacuum module.
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No vacuum. Determine if the vacuum module’s pump is not running. It
should make a humming sound for 90 seconds as it creates a vacuum.
It’s also possible for the vacuum module’s solenoid valve to fail and not
open in which case the accumulated vacuum will not be applied to the
printhead. Check the module’s electrical connection, it runs on 40 VDC
Inspect the vacuum module’s electrical connector; in some cases the
electrical connector can be partially seated, allowing the pump to run,
but not the solenoid valve.
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Vacuum decay too long. If the DECAY time is much longer than
6 seconds, there may be kinked tubing or ink in the tubing to the vacuum
module, or a clogged cap/wipe/purge assembly orifice.
Inspect the tubing for kinks or crimps. To test the tubing for blockage,
disconnect it from the vacuum module. Blow through the tube to ensure
the cap/wipe/purge assembly’s tube orifice or the tubing is not blocked
with ink (there will be some natural resistance to the air you blow, a
blocked tube will be very difficult to blow air through). A defective or
contaminated solenoid valve can cause ink to be sucked into the tubing.
If the tubing is blocked, replace the vacuum module and any parts (cap/
wipe/purge assembly, tubing, filter) that are contaminated.
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Vacuum decays too quickly . Generally, if the vacuum decays too
quickly or immediately drops to zero, the cap/wipe/purge assembly is
making poor contact with the printhead faceplate. Look for improper
cap/wipe/purge assembly belt alignment, printhead-to-drum gap, or
obstructions to the printhead tilt mechanism that prevent the cap/wipe/
purge assembly gasket from sealing properly against the printhead
faceplate. Also inspect the vacuum hoses for leaks and proper fit. Ink
build-up in the cap/wipe/purge assembly, due to poor heating in the
assembly can cause poor cap/wipe/purge sealing as detailed in the next
step.
Alternately, the cap/wipe/purge assembly gasket is bad. With a
flashlight, closely examine the cap/wipe/purge assembly. Inspect the
gasket for defects and signs of separation.