Philips DPTV305, User Manual

Page: 39 / 1848

ELECTRICAL FOCUS ADJUSTMENT
Note: Before beginning the following adjustment procedures set the customer picture, sharpness, brightness,
and tint controls to midrange and the customer color control to minimum.
Electrical Focus Adjustment
1. Remove the back cover of the set and the light shield, then turn the set on and inject an NTSC
crosshatch pattern signal into the antenna terminal.
Note: The crosshatch pattern will appear clearer if the front of the screen is covered with a dark cloth.
2. Cover two of the CRT output lenses with cardboard pieces (or other non-conductive opaque material) to
observe the magnified reflection of the other picture tube on the back side of the viewing screen.
3. Adjust the CRT’s focus control (located on the Screen/Focus Control Block) for the sharpest raster
image.
4. Confirm correct focus by viewing the screen from the front of the set.
5. Repeat steps two through four to adjust the focus of the two remaining CRT’s.
Note: Before beginning the following adjustment procedures, set the customer picture, sharpness, brightness,
and tint controls to midrange and the customer color control to minimum.
OPTICAL FOCUS
1. Remove the back cover of the set and the light shield, then turn these on and inject an NTSC
crosshatch pattern signal into the antenna terminal.
Note: The crosshatch pattern will appear clearer if the front of the screen is covered with a dark cloth.
2. Cover tow of the CRT output lenses with cardboard pieces (or other non-conductive, opaque material)
and observe the magnified reflection of the other picture tube on the back side of the viewing screen.
3. Loosen the lens retaining wing nuts on the CRT Focus Assembly.
4. Move the wing nut in the slot of the uncovered lens to locate the optimum optical focus (viewing the
picture from the back side of the screen), then re-tighten the wing nut.
5. Confirm correct focus by viewing the screen from the front of the set.
6. Repeat steps two through five to adjust the focus of the two remaining CRT’s.
Picture Tube Replacement
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, the lenticular screen, and fresnel lens. 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.