Changhong Electric 21BM91, Руководство по обслуживанию, Страница: 11 / 58

SERVICE MANUAL
3. High Voltage Inspection
Measure voltages of test points on the main PCB 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 below.
Table 3
Test Point Voltage (V)
Negative of VD603
25
±
1.5V
27
±
1.5V (for BSC68V1 FBT only)
Negative of VD855A 190
±
5.0V
CRT anode
25
±
1.5KV
Heater 6.3
±
0.3Vrms
4. Focus Adjustment
Caution: Dangerously high voltages are present inside the TV. Extreme caution should be
exercised when working on the TV with the back removed.
4.1 After removing the back cover, look for the FBT on the main PCB. There should be a FCB on the
FBT.
4.2 Power on the TV and preheat it for 15 min.
4.3 Receive a normal TV signal. Rotate knob of the FCB until you get a sharp picture.
Before Adjusting After Adjusting
Fig. 4
5. Safety Inspection
5.1 Inspection for insulation and voltage-resistant
Perform safety test for all naked metal of the TV. Supply high voltage of 3000V AC, 50Hz (limit
current of 10mA) between all naked metal and cold ground. Test every point for 3 sec. and ensure
no arcing and sparking.
5.2 Requirements for insulation resistance
Measure resistance between naked metal of the TV and feed end of the power cord to be infinity
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