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Electrical Alignments GB 87 EM3E 8.
8. Electrical Alignments
Index of this chapter:
1.
General alignment conditions.
2. Hardware alignments.
3. Software alingnments.
4. Option settings.
Note: The Service Default Mode (SDM) and Service
Alignment Mode (SAM) are described in chapter 5. Menu
navigation is done with the 'CURSOR UP, DOWN, LEFT or
RIGHT' keys of the remote control transmitter.
8.1 General Alignment Conditions
Perform all electrical adjustments under the following
conditions:
•
Power supply voltage: 230 V
AC
/ 50 Hz (
±
10 %).
• Connect the set to the mains via an isolation transformer
with low internal resistance.
• Allow the set to warm up for approximately 20 minutes.
• Measure the voltages and waveforms in relation to
chassis ground (with the exception of the voltages on the
primary side of the power supply).
Caution: never use the cooling fins / plates as ground.
• Test probe: Ri > 10 M
W
, Ci < 20 pF.
• Use an isolated trimmer/screwdriver to perform the
alignments.
8.2 Hardware Alignments
Figure 8-1
8.2.1 Vg2 Adjustment
Method 1 (without oscilloscope)
1.
Activate the SAM.
2. Select ‘Alignments’.
3. Select the ‘General’ sub-menu.
4. Set ‘Vg2 Test Pattern’ to ‘On’
5. First turn the Vg2 potmeter on the LOT (see Fig. 8-1) to
the left (OSD feedback will show ‘Out high’).
6. Turn the Vg2 potmeter slowly clockwise until you read ‘In
low’. This is the correct value.
Method 2 (with oscilloscope)
In the frame-blanking period of the R, G and B signals applied
to the CRT, the ‘HOP’ video processor inserts a measuring
pulse with different DC levels. Measure the black level pulse
during the vertical flyback at the RGB cathodes of the CRT.
1.
Go, via the MENU key, to the normal user menu, select
PICTURE, and set CONTRAST and BRIGHTNESS to 0.
2. Activate the SAM.
3. Connect the RF output of a pattern generator to the
antenna input. Test pattern is a 'black' picture (blank
screen on CRT without any OSD info).
4. Set the channel of the oscilloscope to 50 V/div and the
time base to 0.2 ms. Use external triggering on the
vertical pulse (caution: use e.g. R3641 ,which is at the
‘cold’ side!).
5. Ground the scope at the CRT panel (‘cold’ side) and
connect a 10:1 probe to one of the cathodes of the
picture tube socket (see diagram F).
6. Measure the cut off pulse during first full line after the
frame blanking (see Fig. 8-2). You will see two pulses,
one being the cut-off pulse and the other being the white
drive pulse. Choose the one with the lowest value, this is
the cut-off pulse.
7. Select the cathode with the highest V
DC
value for the
alignment. Adjust the V
cutoff
of this gun with the SCREEN
potentiometer on the LOT (see Fig. 8-1) to the correct
value (160
±
3 V
DC
).
8. Restore CONTRAST and BRIGHTNESS to normal
(CONTRAST= 63 and BRIGHTNESS= 34).
Figure 8-2
8.2.2 Focusing
1. Tune the set to a circle & crosshatch test pattern (use an
external video pattern generator).
2. Choose picture mode ‘NATURAL’ with the ‘SMART
PICTURE’ button on the remote control transmitter.
3. Adjust the FOCUS 1 potentiometer (upper potmeter, see
Fig. 8-1) until the horizontal and vertical lines at 1/4 from
east and west, at the height of the centre line, are of
minimum width without visible haze.
4. Adjust the FOCUS 2 potentiometer (middle potmeter,
see Fig. 8-1) until the horizontal and vertical lines at 1/4
from north and south, at the height of the centre line, are
of minimum width without visible haze.
CL 16532044_013.eps
090501
Large Signal panel (LSP)
SSB
V.SHIFT CINCH SCART
TUNER
3642
1502
5430
Focus 2
Focus 1
Screen
VG2
LOT
Warning
All alignments
are on hot-part !
A
B
C
0V Ref.
CL 06532130_014.eps
131000
V
CUTOFF
[V
DC
]
max.
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