SERVICE MANUAL
Document No
Date of Origin
Date of REV
51-L-DSR004
98-10-21
PAGE REV.
0
PAGE
34 /102
S-00-005(96.03.27)
REV.1
7-8. RF Mod u l a t o r
7-8-1. Check the DC level of
I C
2
(MODSCL,MODSDA)
line of the RF modulator
input with an Oscilloscope,
this point always be high (4.4 ~ 5V).
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 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.
+5V
: Junction
of C104 & C105
VT
: Junction
of C103 & L106
LNB
: TP100
