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Marquee LC Tube Replacement |
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Applicable Models are M8500LC, M9000, and M9500LC and LC Ultra.
These procedures are presented for reference by experienced projector technicians who may be
new to the Marquee chassis or for those seeking a review of the steps needed to replace a Liquid
Coupled CRT assembly. These procedures are not advised for beginners! Handling of Cathode Ray vacuum
tubes entails the risk of injury from flying glass fragments. Also, the required yoke alignments
following reassembly involve reaching next to Lethal Voltages on the tube neck. Anyone attempting any
of the described procedures is doing so at their own risk.
Disassembly will consist
of several stages, including removal of some outer cosmetic
covers, disconnection of anode and yoke lines to the tube,
removal of the neck board from the tube, removal of the
lens, and finally the removal of the tube or tubes that
are in need of replacement. If employing replacement tubes
acquired without magnetics or covers, those items can
be transferred from the original tubes but this will necessitate
alignment of the magnetics afterward, which does bring
risk of electric shock. A fussy alignment of tube yokes
after returning the projector to its' point of use is
desirable for best image quality anyway. Removal of hot
glue from the rear edge of the focus yoke and from the
gap between focus yoke and convergence yoke is recommended,
or alignment will be hampered.
Read our Tech Tip 9, "Marquee
Magnetics Alignment" for more info. If your replacement
tube(s) are second-hand then it is advised to inspect
closely for excess glycol pressure in the bellows; test
by pressing inward with fingers on each side of the black
rubber bellows; if the bellows is firm, not spongy to
the touch, then we advise venting an ounce or two of fluid
out of the fill holes, or one faces the risk of having
the excess pressure cause a cracked tube face (tube destroyed)
or leaking of the glycol out into the chassis, two extremely
bad problems that are worth avoiding. Tubes with clouded
glycol or with debris in the glycol are better if the
glycol is flushed and refilled with new glycol, contact
us if you need this done.
Okay, ready? UNPLUG the AC POWER CORD from the front panel!
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Begin by lifting up the front of the gray metal lens cover, it is held by snaps in front
and tabs in the rear, pull it forward and set it aside. (see Pic 1)
Next, carefully remove the foam lens surround by pulling it forward and away, it is foam rubber
and is easily torn, and remove the spreader bar just above it held by two small phillips screws. (see Pic 2)
Two phillips screws secure the main gray top cover (see
Pic
3), loosen the screws and slide that cover rearward
and set it aside. A machined plate (see Pic 4) is positioned
across the tops of the tubes, just above and behind the
lenses, this machined plate adds mechanical rigidity and
provides pivot pins for the red and blue CRTs; it is held
to the tubes by four allen bolts. (see Pic
5) The middle two bolts may have small red caps on
them, pull the caps off if present and remove all four
bolts and their washers with a 3/16" allen driver. When
necessary to pivot the red and blue tubes for mechanical
convergence, one loosens one allen bolt at the top, and
two more bolts atop the foot of each tube casting just
under the lens, marked "C" on our green tube, and one
then tightens those bolts when aligned.
Remove one phillips screw (see Pic 6) atop each side panel to access the
machined plate. If replacing red or blue tubes, the white plastic side panel and also the inner metal panel will need to be removed for that side, these
are held by a few screws along each side. Do not mix coarse and fine threaded screws during reassembly.
The thin white sheet is a lead x-ray shield, it can stay
with the plate. |
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The plate aligns the tubes with
small pins facing down, these can bind a little so pry
up just under the plate with a screwdriver if needed.
(see Pic 7 and Pic 8)
Note the bolt holes and locator pin holes atop each tube,
the plate needs to mate with these pin holes later during
reassembly. (see Pic 9)
Tube replacement can be done on a ceiling with a bit of
care and someone to assist. This is made easier by first
removing the lens for any tube being replaced. Each USPL
lens barrel is near ten pounds in weight and is secured
by allen bolts at the NE, NW, SE and SW compass angles,
do not remove the other allen bolts!
Using a long 9/64" allen driver, remove the two allen
bolts (see Pic 10 and
Pic 11) closest to the floor first,
then the upper two while someone holds the weight of the
lens barrel so not to fall. This applies to a projector
on a table also.
Pull the lens barrel straight forward and away (see
Pic 12)
so the element bulging out the rear does not scrape
anything and become ruined; the lenses are very costly.
If setting the lens barrel face down, take care it is
not set down on a screw or anything that can touch the
front element. Never set the lens down on the rear bulge,
that will destroy it.
The Horizontal Deflection Module rests
in a metal sleeve between the green and blue tubes; it
weighs several pounds and can fall from a ceiling; unplug
the three yoke couplers, making note of the orientation
at the coupler and also note that red is frontmost, green
in the middle, and the blue yoke is at the rear. If these
are mixed up then static horizontal convergence will not
function correctly, as that is a DC offset voltage applied
to the scan yokes, same for vertical. Remove the HDM board
(see PIC 13) and set it aside. |
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We must now access the neck board
to remove it; this is best done by opening the rear heat
sink, it is on a hinge; remove four phillips screws across
the edge of the heat sink. Note the braided grounding
straps, they will need to be reinstalled later. (see Pic
14 and Pic 15) If on a ceiling, tie the heat sink up out
of the way with twine or wire. Neck boards must be removed
from the tube necks to allow tube removal; the covers
that secure the neck boards must be removed (see Pic 16),
they are held by two small screws; note the grounding
straps that need to be secured to the heat sink during
reassembly.
Here we see the video final amplifier card, or "neck board"
(see Pic 17 and
Pic 18) because it plugs onto pins protruding
from the rear of the tube neck itself. The black lines
with blue lug connections are called Aquadag grounds (see
Pic 19) operation of the tube without these will destroy
a neck board instantly. The lugs must fit the ground tabs
tightly, crimp the lugs some with a pliers to ensure very
snug contact. Needlenose pliers are useful to remove or
crimp these, pull the lug end upward to undo. (see
Pic 20). |
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The white jumper wire into the
end of the tube carries 500+ volts of G2 bias current,
make sure to reconnect to the tube pin closest to the
base of the jumper or the tube can be damaged. (see
Pic 21).
If connected wrong the tube will flash violently;
power down at once and recheck all connections. At reassembly,
crimp the round end of the jumper until slightly oval
for a snug fit. (see Pic 22)
The green-tipped wire closest to the G2 jumper is the
G2 feed, it is a lug and can only fit at that point. (see
Pic 23) The G2 feed originates in the high voltage power
supply.
The green-coded line with metal plug tip is low level
video from the input section and it can only connect to
the matching socket, the plug looks like a miniature phono
or RCA type plug. (see Pic 24) This feed originates in
the VIM input section on the rear panel.
The fourteen-pin molex connection below that carries power
and ground connections and also some protection signal
lines; the VNB can detect excess beam current in the tube
and limit the current to shut down the beam before the
tube is ruined. Tubes that have suffered phosphor scarring
in small lines may have spot kill circuit problems; this
circuit must be operating or the replacement tube will
be similarly ruined, do not proceed without having spot
kill function confirmed or repaired.
Note also on your neck board a ground wire at top that
gets secured back to the cover screws, and a ground lug
to the sheet metal below the fourteen-pin molex, this
is a tab connection for ground.
All electrical connections to the tube must be undone;
the 34.9kv high voltage anode splitter sits atop the green
tube cover and can be accessed by loosening two phillips
screws that secure it. (see Pic 25)
The anode wires carry Hobson bayonet connectors (see Pic
26); turn them to the left and pull away. A pair of needlenose
pliers can engage the grooves on each side for removal.
The metal tip of the anode wire can carry several thousand
volts stored inside the tube, even days after the tube
was last operated, so be aware that a jolt is possible
though not likely lethal. Hobson connectors must be firmly
snugged on the anode lines of the replacement tubes, or
high voltage arcing may occur. |
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Three focus yoke molex connectors
(see Pic 27 and
Pic 28) plug into the focus board which
sits opposite the HDM, also in a sleeve. Remove the focus
molex for the tube being removed and for any yoke wires
which are in the way.
Except for HDM and Vertical Sweep, the other Molex connectors
are meant to only plug onto the pins in one orientation;
if it needs to be forced then it probably is not turned
correctly, try flipping the plug over. Do not mix red
with green with blue; every Molex is tube-color-specific.
The stigmation yoke plugs have gray/blue/violet/white
wires (see Pic 29), unplug each stig yoke for the tube(s)
being removed; remove any small white nylon wire tie clips
if installed.
Next unplug the convergence yoke for any tube(s) being
removed. (see Pic 30) These wires are orange/brown/violet/black.
The vertical yoke has a green/yellow wire pair which may
be flipped to REV SCAN mode for some mounting positions;
note the mode you are starting with if unplugging all
three yokes at the same time; these are color-specific
as static vertical convergence is delivered thru sweep
with a DC offset voltage. (see Pic 31 and
Pic 32)
We should now be free of all electrical connections between
tube and chassis. These lines can be bundled with tape
or rubber bands to prevent snagging as the tube is removed,
this is recommended if coming down from a ceiling. (see
Pic 33) |
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With all electrical connections
detached and the neck board removed, all that holds
the tube in the chassis is two 1/4-20 allen bolts as
shown. If the projector is on a ceiling, one must get
assistance to hold the 15 pound weight of the tube as
these two bolts are removed, never try this without
a helper. Use a 3/16" allen driver to undo the bolts.
(see Pic
34) They are labeled "C" on our green tube.
With the tube lifted (or lowered) clear, note the base
it sat on, a locator pin on the plate below will need
to engage a hole in the base of the replacement tube
as a pivot pin and so the bolts can line up to the tube
casting. (see Pic
35 and Pic
36)
If re-using original tube covers or tube magnetics,
they can be removed from the old tube now; a 3mm ballnose
allen driver and a medium phillips screwdriver will
be needed, see our website for a review of yoke alignments
at http://www.etechvideo.com/ and visit Tech
Tip 9. See also our Tech Tip titled "Preparing
Marquee LC Tubes for Installation".
Red and blue tubes
usually have X-Ray shields at one side, undo the two
screws and small metal plate and move the shields to
the tube(s) being installed.
LC lenses and adjustments will
be covered in a future Tech Tip, these can be found
also in the Marquee Users Manual for LC models.
We also advise, for projectors mounted upside down,
to redo the lid of the HDM sleeve cover by removing
the white foam material, which is usually crushed and
flimsy, and install 7 or 8 layers of duct tape or similar
as a pad to support the weight of the HDM board so not
to fall out of its' socket and cause a stoppage. A 3mm
pad should do, and leave a small gap for the sleeve
edge to contact the cover and still support the board
edge. (see Pic
37) |
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Tim at E-Tech Systems Phoenix 480
368 7434 |
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