Haier HT-3718 Service Manual page 26

Table 6
Step
1 B IN
2 R IN
3 G IN
4 GND
5 F/B
6 VCC
7 G OUT
8 R OUT
9 B OUT
7). Analysis of switching mode power circuits
The installed switching mode power source is a typical autonomous pulse switch power source.
The circuits are comprised of IC N501, switching mode transformer T501, bridge-rectifier
components. When the switch is set to on, the pulse voltage of the 220V voltage rectified by
VD503-VD506 rectifier is filtered by the capacitor C511 (1500uF) to obtain +300V direct current,
which is added through (3)-(7) of the switching mode transformer T501 to the pin1 of IC N501.
When the appliance is first switched on. The coupler VD507 (PC817B inlet) functions to control
voltage, and the voltage tolerance information from T501 are transmitted to pin4 of N501 via
VD507 to control the switch velocity and hold the output voltage normal.
The pulse voltage output from the secondary (12) of the switching mode transformer T501,
rectified and filtered by V511(RU3A) and C522 is +110V direct current voltage which is
horizontal voltage. The pulse voltage output from (14) is rectified and filtered by VD512 and
C526 and the resultant +24V direct current voltage is supplied for sound power amplifier. The
pulse voltage output from (15) is rectified and filtered by VD515 and C537 and the resultant
+12V direct current voltage is supplied to the little signal circuits. The pulse voltage output from
(15) is rectified and filtered via V509 and N507 to obtain +8V direct current voltage to supply
the decode circuit of IC N201. +12V direct current voltage output, after rectification of the
secondary source, +3.3V and +5v are supplied to N201 and EEPROM.
FUNCTION
Working Ground Resistance (R)
Voltage
Positive
V
2.9
2.9
2.9
0
3.8 13.24K
164.9
114.5
114.2
113.4
26
Circuit Explanation
Negative
5.44K 5.43K
5.44K 5.45K
5.38K 5.39K
0 0
13.3K
34K 30K
2.1M 3.24M
1.8M 3.22M
2.1M 3.22M