Haier HT-3718 Service Manual page 24

Step
56. VDD.C
57. OSC.GND
58. XTAL.IN
59. XTAL.OUT
60. RESET
61. VDDP
62. AV1
63. AV2
64. IRin
2). Analysis of common path circuits
High frequency television signals, received via an antenna (or transmitted through a cable
TV system) to the input terminal of the high frequency tuner U101, are processed for tuning
and high frequency amplifying and mixing, then a 38.9MHz image intermediate frequency and
31.5MH sound intermediate frequency signal will be released at the IF terminal of TU101 to b
Z
of the transistor V101 , where signals are amplified to compensate for the insertion losses of
the sound surface wave filter. Single or dual-ended input is used for the sound surface wave
filters Z101 of this appliance according to system properties. Intermediate frequency signals
will be transmitted to (23) and (24) of N201(TDA9361). High frequency amplify AGC output
from (27) of N201 controls the gain of the high frequency tuner.
3). Analysis of signal trap switch circuit
Color video signal output from (38) of N201 through V250 to Z250-Z252 and Z255.All television signal
is selected by V255 and V256 then pass.V255 and V256 are band-pass transistors, take part in switch at
the location. The pin 5 of N201 is high level (sound frequency isn't 4.5MHZ ), V256 conducts the signal
pass through Z250-Z252 channel. When pin 6 of N201 is low level. V256 cut off and V255 conducts,
the signal pass through Z255 channel. After the all television signal pass through the traps, video signal
is gained, then after it pass through R260, R261,C242,N201(pin 40), V403 , it is used in AV output.
Video signal of AV and Y signal of s-terminal pass through N401 (HEF4053BP) are selected and go into
pin 42 of N201; C signal of s-terminal go into pin 43 of N201.
R,G , B signal of RGB component respectively pass C291, C260, C261 to couple, go to pin 46, pin 47,
pin 48 of N201.
4). Analysis of sound power amplifying circuits
Sound power amplifying circuits are composed of integrated circuits N301 (LA4285/87) and
N302 (LA4285/87) peripheral components. LA4285/87 is an integrated electrical circuit .
Information introducing functions and testing data for LA4285/87 maintenance is listed in Table
Function
24
Ground Resistance(R)
Working
Positive
Voltage
V
3.1 30K
0 15.4
1.5 1.17M
1.6 0.74M
0 0
3.1 30K
4.8 12.8K
4.8 12.8K
4.9 36.9K
Circuit Explanation
Circuit Explanation
Negative
26.2K
14
262K
227K
0
26.2K
12.9K
12.9K
34.6K