Comb Filter Alignment; Sub-Brightness Adjustment; Dynamic Gamma; High Voltage Frequency Adjustment - Philips PTV400 series Service Manual

Comb Filter Alignment (this adjustment requires the use of
equipment
not normally carried into the home)
Note: The following procedure covers the only Field Adjustable
Controls contained within the CCD Comb Filter Module. These
are also the only controls accessible through holes provided in
the top shield of the Module.
1. Apply a Color Bar signal from a Color Bar Generator to the Tuner
Input,
2. Connect an Oscilloscope to TP34.
3. Adjust R20 for minimum color sub-carrier as seen on the
oscilloscope.
4. Adjust R56 for minimum color sub-carrier as seen on the
oscilloscope. Repeat steps 3 and 4 for best results.
Sub-Brightness Adjustment
Note: Refer to the Gray Scale Tracking and Sub-Brightness
procedure contained later in this section for the precise setting
of all interrelated controls.
Dynamic Gamma (this adjustment requires the use of equipment not
normally carried into the home)
1. Apply a Crosshatch pattern utilizing 1001RE (100% white) to the
antenna terminals (Very important step, anything less than 1001RE
will not work correctly).
2. Tune set to this signal and adjust the Customer Brightness and
Picture Controls to maximum.
3. Set the Gamma Adjust Control (R603) to its full counterclockwise
(CCW) position.
4. Display the main customer menu on the screen. Note the blue
bleeding at the blanked boarder area on the left-hand edge of the
menu.
5. Rotate the Gamma Control (R603) slowly clockwise (CW) to just
eliminate the blue bleeding in to the menu area.
High Voltage Frequency Adjustment (this adjustment requires the
use of equipment not normally carried into the home)
1. Turn the set Off and disconnect power supplied to the chassis.
2. Undo cable restraints and fold the chassis down (in order to gain
access to the copper side of the module).
3, Locate the copper pad for TP67 and solder a short piece of wire
onto it.
4. Connect a jumper lead to this test point and connect the other end
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to ground.
5. Connect a Frequency Counter to Test Point TP38.
6. Turn On the set and adjust R902 to obtain a reading of 15.734kHz
on the counter.
7. Disconnect test equipment and remove the short from TP67.
Note: Some Frequency Counters may be too sensitive at one
attenuation level and not sensitive enough at the other level. In this
case, an oscilloscope may be used. Adjust R902 to obtain a 63.5uSec
delay from the leading edge of the first main vertical pulse to the
leading edge of the second main vertical pulse.
Video Level Alignment (this adjustment requires the use of
equipment not normally carried into the home)
1. Apply an NTSC Color Bar Pattern Signal to the antenna terminals.
2. Tune the receiver to the applied signal in step 1.
3. Connect an Oscilloscope to the emitter of Q200 (Test Point TP1)
and adjust the Video Level Pot (R244) until the video signal
observed on the Oscilloscope is 2Vp-p +/-50mV.
Vertical Height Adjustment (this adjustment requires the use of
equipment not normally carried into the home)
1. Apply a crosshatch pattern to the antenna input terminals.
2. Adjust the Vertical Height Control (R551) to obtain a slight
underscan of the raster at the top and bottom of the screen.
3. Adjust the Vertical Height Control (R551) to obtain a slight
overscan at the top and bottom portions of the screen
(approximately 8% overscan total or near 3/4 inch).
Vertical Blanker Adjustment
Some television stations transmit additional information such as
Vertical Interval Test Signals (known as VITS), on video lines 20 and
21. VITS, Closed Captioning, and other information may occupy these
lines. Normally, this additional information causes no objectional
distortion on the screen as it is transmitted during the vertical blanking
period. When distortion from this additional information does appear
on screen, it usually shows up as a bright white line at the very top of
the screen. The Vertical Blanker Control (R802) eliminates this type of
distortion by adjusting the vertical blanking time to eliminate this white
line from the top of the screen. In order to properly adjust this control,
you must first tune to the channel exhibiting this type of distortion on
the screen. Adjust R802 to just eliminate the white line. Increasing the
blanking time any further will cause a loss of standard video
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