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Picture Tube Replacement
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Tip from GB:
Replacement of the cathode ray tube (CRT) and/or optical system components of a
Projection TV (PTV) can be easily accomplished by following general guidelines.
Use care when working around the CRT and optical systems of the PTV. The PTV light path
encompasses a number of precision optical components. These include lenses, mirrors, and
lenticular and fresnel screens. The PTV incorporates three separate CRTs, representing
green, red, and blue outputs.
Each CRT uses an independent deflection/convergence yoke, magnetic centering ring,
coupler, C-element lens, and output lens (A/B lens). Each tube is mechanically fastened to
a coupler which houses fluid (a glycol-type substance) used to cool the high temperatures
generated by the small (7") CRTs. The fluid also provides an optical characteristic
supporting the optical system of the PTV.
When replacement of a CRT or optical component is required, caution must be exercised
in preventing fluid spillage. The technician must carefully reassemble the CRT/optical
components, ensuring a proper seal of the coupling fluid. Use only factory original
coupling fluid.
Caution: Do not use or add water as an alternative to the prescribed coupling fluid.
The following procedure should be used when performing repairs on the CRT/optical
assemblies of the Projection TV.
Note: Upon completion of CRT/optical assembly repair, the centering, convergence, gray
scale, mechanical and electrical focus adjustments are required. If more than one assembly
requires repair, it is recommended the service technician fully complete one assembly at a
time, using the existing assemblies as a reference for the alignment of the centering and
convergence.
Disassembly Procedure
A. Removal of a single CRT/Lens Assembly from the light rack
1a) Remove AC power from the PTV.
2a) Remove the upper and lower back covers (1/4" screws).
3a) Remove the barrier board and the shield cover from around the lens assemblies
(1/4" screws).
4a) Carefully remove the CRT Socket Board from the CRT of the CRT/optical assembly
being serviced.
5a) Remove the yoke plug from the Large Signal Module and the convergence yoke plug
from the Digital Convergence Module of the CRT/optical assembly being serviced.
6a) Remove the high voltage anode lead from the HV splitter block on the Large Signal
Module of the CRT/optical assembly being serviced. Remove ground lug connectors from the
coupler frame.
7a) Remove the four 1/4" screws that secure the CRT/lens assembly to the light
rack. These four screws are located in each corner, on the top of the coupler
assembly.
Caution: Do not remove the bolts with pressure springs or the inverted Torx screws of
the CRT/lens assembly. The removal of these components could result in fluid spillage into
the PTV cabinet.
8a) Carefully remove the CRT/lens assembly from the PTV cabinet.
Servicing the CRT/Optical Assembly
The following procedures describe how to service the Delta 77/78 CRT/optical
block.
Caution: Do not attempt any repairs on the CRT/optical
block assembly without first removing the CRT coupling fluid. Removal of the delta output
lens will result in spillage of the coupling fluid.
Caution: Coupling fluid is a poisonous solution containing
a high concentration of ethylene glycol. Do not leave exposed fluid unattended. Prevent
children or pets from coming into contact with the fluid. Clean up spills immediately.
B. Removing the PTV Coupling Fluid
All repairs made to the CRT/optical block assembly require the removal of the
coupling fluid. The following procedure describes how to remove the PTV coupling fluid.
1b) Lay the CRT assembly on its side with the plug pointing up.
2b) Remove the plug (K) (1/4 turn to release).
3b) Remove some of the fluid from the coupler to prevent spillage when the CRT is
removed. An empty coupling fluid bottle with a cone top is recommended to lower the fluid
level within the coupler. Squeeze and hold the bottle and insert the tip of the cap into
the drain hole of the coupler. Loosen the grip on the bottle, allowing the fluid to be
pulled up into the bottle. Save the fluid.
4b) Reinstall the plug (K).
5b) Stand the CRT assembly up with the neck of the CRT pointing up.
6b) With an awl or marking pen, outline the edges of the CRT onto the coupler.
Note: The correct positioning of the CRT to the coupler is critical to the optimum
performance of the optical system.
7b) Remove the four CRT mounting bolts (A) (with springs and spacers) and remove the
mounting bracket (D).
8b) Remove the four CRT mounting ear screws.
Note: The CRT mounting ear screws are not used on some assemblies.
9b) Gently remove any metal shavings from around the screw holes. Do not allow the metal
shavings to get into the fluid.
10b) Note the position of the high voltage anode cap with respect to the coupler.
11b) Carefully remove the CRT (E) from the coupler. Wipe any excess fluid from the
faceplate of the CRT. Set the CRT aside.
12b) Use an empty coupling fluid bottle to extract the remainder of the fluid from the
coupler.
Note: Complete removal of the coupling fluid is not necessary when only replacing the
CRT.
13b) Clean any remaining fluid from the coupler and the CRT gasket channel using
absorbent tissue. Refer to "C. Cleaning the Coupler, C-element Lens and CRT
Faceplate" procedure if the fluid is discolored or contaminated.
14b) Make all necessary repairs.
C. Cleaning the Coupler, C-element Lens and CRT Faceplate
1c) Remove PTV coupling fluid as described in steps 1b through 13b.
2c) Using denatured alcohol on a cloth made of 100% cotton or a lens cleaning tissue,
gently clean the C-element (fisheye) lens (S), coupler (P) and the CRT faceplate
(E). Thoroughly clean the coupler assembly, including the expansion chamber bladder,
and allow to fully dry.
Caution: Do not use soap or detergent type substances to clean the coupler and its
related assemblies. Water can be used as an alternative to denatured alcohol, but the
assemblies must be completely dry prior to reassembly of the coupler and the addition of
the coupling fluid. A hair dryer may be used to dry the coupler and its assemblies prior
to reassembly. If contaminated fluid is discovered, the coupler and its related assemblies
must be completely disassembled and cleaned to prevent a reoccurrence.
3c) Replace the CRT (E) and C-element lens gaskets (R).
4c) Reassemble the C-element lens (S) and the output lens to the coupler (P).
5c) Refer to "Replacing the PTV Coupling Fluid" upon completion of necessary
repairs and cleaning of the optical/coupler assemblies.
D. Replacement of the CRT
1d) Remove PTV coupling fluid as described in steps 1b through 13b.
2d) Remove the plastic protective coating (if present) from the faceplate of the
replacement CRT.
3d) Refer to "Replacing the PTV Coupling Fluid" to complete the CRT
replacement.
E. Repair or Replacement of the Optical/Coupler Assembly
1e) Remove PTV coupling fluid as described in steps 1b through 13b.
2e) Remove the four inverted-type Torx screws (X) which secure the Delta output lens to
the coupler. An inverted-type Torx socket can be purchased using part number 483539517303.
3e) Removal of the Delta output lens will allow access to the C-element lens (S),
C-element gasket (R), coupler (P), and its assemblies.
4e) Refer to "Replacing the PTV Coupling Fluid" upon completion of necessary
repairs to the optical/coupler assemblies.
F. Replacing the PTV Coupling Fluid
Note: Prior to replacing the PTV coupling fluid, ensure the expansion chamber bladder
(O) is fully collapsed. This can easily be inspected by viewing the bladder through the
small hole on the expansion chamber assembly. If the rubber of the bladder is not easily
visible through the small hole, then the bladder may be considered collapsed and fluid can
be added. If the rubber of the expansion chamber bladder is visible at the hole of the
expansion chamber, then replacement of the expansion chamber bladder is required.
Note: The CRT coupling fluid is critical to the optical performance of the PTV. Use
only part number 483531057233 (3 bottle kit) or 483531067004 (1 bottle) to ensure the
optical integrity and performance reliability of the PTV when replacing the PTV coupling
fluid.
1f) Reinstall the CRT gasket (N) into the gasket channel of the coupler. Confirm the
placement of the CRT, C-element lens, and vent plug gaskets (L).
2f) Place the CRT onto the coupler with the high voltage anode lead positioned as
marked in step 10b of procedure B.
3f) Carefully position the CRT onto the coupler, using the outline defined in step 6b
of
procedure B as a reference.
4f) Start the CRT mounting ear screws but do not tighten them.
5f) Tighten the CRT mounting ear screws in a star pattern (like tightening lug nuts on
the wheel of a car). Make sure the CRT does not shift position from the outline defined in
step 6b.
Caution: Do not overtighten the CRT ear screws.
Note: The CRT mounting ear screws are not used on some assemblies.
6f) Install the CRT mounting bracket and start the four CRT mounting bracket bolts with
springs.
7f) Tighten the bolts in a star pattern.
8f) Lay the CRT assembly on its side with the plug (K) pointing up.
9f) Remove the plug (K) (1/4 turn to release).
10f) Using the PTV coupling fluid bottle with the cone top, refill the coupler with
fluid through the drain access hole. Completely fill the coupler chamber so the fluid is
level with the top of the coupler at the plug. Wipe any excess fluid from around the
coupler.
11f) Reinstall the plug and check for any fluid leaks.
12f) Install the repaired CRT/optical block assembly into the PTV and perform any
necessary adjustments.
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