Changhong Electric 34T18, Руководство по обслуживанию, Страница: 9 / 61

SERVICE MANUAL
7
CIRCUIT ADJUSTMENTS
Preparation:
Circuit adjustments should be made only after completion of set-up adjustments.
Circuit adjustments can be performed using the adjustable components inside the TV set. For TVs
with I
2
C bus control, first change the bus data.
1. Degaussing
A degaussing coil is built inside the TV set. Each time the TV is powered on, the degaussing
coil will automatically degauss the TV. If the TV is magnetized by external strong magnetic field,
causing color spot on the screen, use a specific degausser to demagnetize the TV in the
following ways. Otherwise, color distortion will be shown on the screen.
1.1 Power on the TV set and operate it for at least 15 minutes.
1.2 Receive red full-field pattern.
1.3 Power on the specific degausser and face it to the TV screen.
1.4 Turn on the degausser. Slowly move it around the screen and slowly take it away from the TV.
1.5 Repeat the above steps until the TV is degaussed completely.
2. Confirmation and Adjustment for Voltage
Caution: +B voltage has close relation to high voltage. To prevent X-ray radiation, set +B
voltage to the rated value.
2.1 Power on the TV and receive Philips test pattern.
2.2 Check the resistors and coils for being burned. (If the fuse is burned out, do not power on the
TV again until the cause is found out.)
2.3 Measure voltages of test points with the digital voltmeter. Measure the CRT high voltage with
the high-voltage testing equipment and heater voltage with the high-frequency effective
voltmeter. The rated values are shown as table 1
Table 1
Test Point Voltage (V)
One Pin of L807 145V
±
1.5V
Positive of C834 12V ± 1V
Positive of C837 12V
±
1V
Positive of C832 16V ± 1V
One Pin of L806 16V
±
1.5V
Positive of C839
3.3 ± 0.3V
Positive of VD822 3.9
±
0.3V
Positive of C429
195V ± 5V
Positive of C436A
48V
±
3V
(Continued)