16
A1 control
This should be set for 150V black level at the tubebase
cathodes with the settings normalised, using the lower
control on the rear of the flyback transformer.
White points
These should be adjusted viewing a picture with little light
area, to prevent beam current limiting. The parameters
should be adjusted for a black to white swing of 65±1V on
each of the three cathodes, with picture normalised.
Text contrast :
White balancing of the red and blue outputs relative to the
green should be carried out to ensure pure white text, using
RV321 (R) and RV322 (B). As the picture outputs are
automatically balanced, text white may be set using picture
white as a reference, once the drives have been set. The
text contrast itself should be adjusted such that the
Text/OSD white parts are approximately 75% of the intensity
of a peak white area of a test pattern; this corresponds to the
75% grey blocks in part of a ‘Philips 5544’ type test pattern.
When the text contrast service parameter is selected the TV
switches to teletext mix mode, page 101; if no text is present
P100 will still appear in the top left corner of the screen
together with some text on the bottom row of the display.
There is no on-screen parameter, adjust with volume control
as normal and change parameter with programme up/down
keys.
IF PLL (AFC)
This should be adjusted with the aerial input grounded and a
38.9MHz signal input direct to the SAW filter (care must be
taken to check whether the tuner output is symmetrical, or
one side grounded). If this is not possible, an approximate
setting may be made using the aerial signal.
The display at the top right of the screen shows two digits,
each 1 or 0. The left hand digit is 1 when the IF frequency is
within an 80kHz window of the centre point. The right hand
digit is 1 when above the exact reference frequency, 0 when
below. Thus parameter 15 should be adjusted to the single
step where the left digit is 1 and the right digit just changes
from 0 to 1.
Important: the range of parameter 15 is 00 to 7F.
When the aerial signal is tuned, the AFC can be seen
stepping over the tuning point once per second ( the right
hand digit changes between 0 and 1 ). If the stepping
remains erratic, recheck the setting. If the change does not
occur, ensure AFC is enabled by using the manual search
tune option in the tuning menu.
AGC
AGC take over point should be adjusted such that the tuner
output to the SAW filter is 600mV
pk-pk
( 300mV per side for
symmetrical tuner output ) without sound.
Focus :
Adjust the upper control on the rear of the flyback
transformer for best focus.
Positioning :
Centre the picture horizontally and vertically and set the
height for 6% overscan ( the edge castellations of the test
card will just show at the edge of the screen). It may be
necessary to readjust after the linearity has been set. The
width is not set by the microcontroller; set for 6% overscan
using the core of L404.
Linearity :
With a test pattern showing equal vertical intervals, adjust
vertical slope for evenly spaced intervals at the top and
bottom of the picture, then adjust vertical S-correction to
even the spacing across the whole height of the picture.
Vertical Protection Disable
Select service parameter OA (S correction) and press the
number 2 key on the hand unit to disable the vertical
protection of IC504. This will isolate the vertical protection
circuit. After repair, vertical protection should always be re-
enabled by pressing the number 2 key again and storing it
with the TV key. (The value of parameter OA toggles
between two values when the 2 key is pressed, the higher of
which indicates vertical guard is enabled).
Auto Black level Disable
Select service parameter 02 (hue) and press the number 2
key on the hand unit to disable automatic black level
sampling in IC504. This isolates the black current signal from
the tube base. After repair, the auto black level sampling
should always be re-enabled by pressing the number 2 key
again and storing it with the TV key. (The value of parameter
02 toggles between two values when the 2 key is pressed,
the lower of which indicates black level sampling is enabled).
