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SERVICE MANUAL
7-8. RF Mod u l a t o r
7-8-1. Check the DC level of
input with an Oscilloscope,
7-8-2. Check the tuning voltage of the modulator pin 1 of Modulator.
this voltage should be 28+/-1V.
7-8-3. Check pin 6 of MOD1(RF Modulator) this pin should be always +5V.
7-8-4. Check pin 4 of MOD1(RF Modulator) this pin is able to control
voltage 0 to +5V by S/W. RF carrier should be outputed when this pin
at +5V condition.
7-8-5. Make sure the audio and video signals are going to the RF modulator
input
7-8-6. The pins should be 2 for video and 3 for audio(the pin of MOD1 RF
modulator).
7-8-7. if all of the Moduluator pin are normal then replace the Modulator.
7-8-8. if there are no audio and video signal when after Replace Modulator
then Keep checking the signal path referring to the schematic
diagram and find PCB pattern's open or short and defective component
to replace.
7-9. QPSK
QPSK Module delivers MPEG TS to the output decoding the STB's Front-End input
signal such as Tuning, Acquisition, Tracking, Demodulation and FEC.
QPSK Module's defects can be divided in two types.
- Tuning Defect : PLL Control of the Tuner does not work properly.
- Tracking Defect : The Operations of the Tuner and QPSK Demodulator IC are
not done properly.
7-9-1. Tuning Defect
7-9-1-1. Check the Tuner's Operating Voltage as follows.
S-00-005(96.03.27)
+5V
: Junction of C104 & C105
VT
: Junction of C103 & L106
LNB
: TP100
REV.1
2
(MODSCL,MODSDA)
I C
this point always be high (4.4 ~ 5V).
PAGE REV.
51-L-DSR004
Document No
Date of Origin
Date of REV
line of the RF modulator
0
PAGE
98-10-21
34/102
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