Rf Modulator; Video; Audio; The Advanced Test Of Front Board - Topfield TF4000FI Service Manual

Set the LNB voltage to Horizontal
- Check Point –
Check level of U3.5 whether logically 'HIGH' ( about 3V ). If logically 'LOW' ( about 0V) then check the
line from U5 (IBM39STB02500 ) and U3.5.
Check level of U3.6 whether logically 'HIGH' ( about 3V ). If logically 'LOW' ( about 0V) then check the
line from U5 (IBM39STB02500) and U3.6.
Check the voltage of U3.4. That value must be over 20V. Voltage of U3.4 is under 20V, then check
soldering status of U3.

5.3.6. RF modulator

- Check point 1 -
Check the power input of RF modulator (U21, Schematic page 11).
- Check point 2 -
Check the IIC line.(the signal name is SDA5V, SCL5V).

5.3.7. Video

- Check point 1 -
Check video output of Chinch, and RF modulator.
Check L13 and its related circuit (CVBS). At this point the signal should be work. If it does not work well,
the IBM39STB02100 (U5) may have problem.

5.3.8. Audio

- Check point 1 -
Check audio output of Chinch and RF modulator. If only on of them has problem, check its related circuit.
- Check point 2 -
Check U17.1 and U17.7. If it does not have audio signal, the Audio DAC(U18) or OP AMP(U17) may
have problem. To check audio DAC, check C44 and C47. If it has audio signal, the OP AMP(U17) is the
problem.

5.4. The Advanced Test of Front Board.

5.4.1. Remote control

U1 is the sensor for remote control.
- Check point 1 –
Check the Remote control unit with other receiver. If it does not work, the Remote control unit may have
problem.
If the key and display work and only the remote control does not work, U1(sensor) may have problem.
Check the power of the sensor (U1.3). It should have 5V. If not, check the R1 and the PCB.
- Check point 2 –
If you can not find any problem with the U1.3, replace it with new one.
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