Strong SRT4155Evolution, Service Manual

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In case of Vert Polarity
?
Check Point : R125
LNBA
?
Check Point : L106, (13V)
Failure Causes and Solution
If there’s no 13V or 18V on the output connector of Tuner U101, you should check High(3.3V)/low(0V) state of R121.
And this is properly high then check the Q107, U105 and Q109 respectively.
2. I2C Control Signal
SCL_NIM
?
Check Pont : U301 Pin 20
SDA_NIM
?
Check Point : U301 Pin 21
Failure Causes and Solution
If there’s no or different signal compare to above picture on I2C line, check the associated net. Try to remove serial resistor
R205, R206, R351, R352, R549, R550, R581 and R582, then if you could find what device has problem.