Haier 29FV6 Service Manual page 19

Circuit Explanation
is operational with dual power supply, forward and backfly power supply, obtained through
line output amplification and of +14V and -14V, respectively.
4. Muting circuit and shut-down silence circuit
The muting circuit enables N901(CPU) to generate high level to raise the power level of
pin 10 of N602 (for left and right audio channels control) and pin 9 (for bass sound control)
to achieve the muting result (output at high level of pin 10 and 9 of N602 is 0V). When
channels are changed, CPU sends high level (high level takes a bit longer time than
channel option.) to realize the mute effect of N602 while changing channel and then
eliminate the noise when changing channels.
Shut-down silence circuit works by changing +15V to 0 while the TV set is turned off, and
C641 discharges to enable V602 through and, as a result, to raise the voltage of pin 10
and 9 of N602 for a mute result.
5.Geomagnetism calibration circuit
Working principles: Geomagnetism calibration is to utilizing the stable magnetic field
generated by direct current volts of geomagnetism calibration coils to solve the problem of
picture incline resulted from different geomagnetism in different places. In most cases, it is
to use two constant voltages for the calibration. This circuit is to use +15V direct voltage
provided by line package and PWM wave generated by CPU for geomagnetism
calibration.
Details of the circuit: Audion V950 and V951 function as switch on and off. When V950
base electrode is of high level, V950 on, V951 off, C903 discharge through R901 and
V950. C902 recharge through R902 and R904. When V950 base electrode is of low level,
V950 off, V951 on, and C903 recharge through R903 and R901. C902 discharges through
R904 and V951. Correcting PWM wave duty ratio may diversify switch-on and off time of
V950 and V951, and discharging or recharging time of C902 and C903, and voltage
accumulated in C902 and C903, resulting in different output voltage.
Following are the data of some circumstances:
When geomagnetism calibration status is –50, PWM duty ratio is about 1 (almost high
level), V950 B/C/E voltages are 0.77V, 0.1V and 0.01V (through), respectively, V951
B/C/E voltages are 0.06V, 12.21V, 13.35V and 11.94V, respectively. Voltages at two ends
of the calibration coil are 11.94V and -0.01V, respectively.
When geomagnetism calibration status is 50, PWM duty ratio is about 0 (almost low level),
V950 B/C/E voltages are 0.12V, 14.46V and 0.01V (Off), respectively, and V951 B/C/E
voltages are 0.72V, 0.15V and 0.01V (through), and V952 B/C/E voltages are 0.15V,
14.082V and -0.06V, respectively. Voltages at two ends of the calibration coil are -0.06V
and 14.029V, respectively.
All and all, when geomagnetism calibration data changes from –50 to +50, voltages at the
two ends of the calibration coil will also change from 11.94V to -0.06V and from 0V to
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