[ Example 4 ] Symptom: noise when tuning.
Description: radio station has noise when tuning.
Analysis and troubleshooting: firstly judge whether the tuning components or common part has
trouble. Listen to radio station by using headphone and check whether only one side of headphone has
sound and the result is normal. Then switch in tuning state to search radio station automatically and the
result is normal, which means power supply, data and clock are normal. To remove interferences from
outside, we receiver the nearest radio station to listen and check whether it is clear, and it has noise in
result. The circuit that causes noise is mainly high frequency tuning and mixed frequency part. Check
carefully and find that pin 37 of U1 (TEA5767HN) has false welding. After welding again, trouble is
removed.
[ Example 5 ] Symptom: no sound when pressing button.
Description: no click sound when pressing buttons.
Analysis and troubleshooting: if no click sound when pressing buttons, firstly check whether sound
of pressing button has been opened. After confirming it is opened, check whether buzzer is normal. Use
resistance level of multmeter to test and the resistance is ten-ohm and more, which is normal. Check J3
end voltage 1.6V and it is normal. When pressing buttons, test DIDI signals and find there is no change.
Check whether crystal oscillator U10 oscillates normally and there is no oscillation. After changing U10,
trouble is removed.
[ Example 6 ] Symptom: no OSD.
Description: screen has no display.
Analysis and troubleshooting: firstly confirm whether power or display screen itself has trouble.
Power on, listen to playing sound and it is normal, so we preliminarily decide power supply 3.3V and
1.8V are normally basically. Test voltage on two ends of L10 and it is about 4.3V, which is normal. Then
test voltage on two ends of D8 and find the anode does not form 13V. Take out display screen and there
is still no 13V. Check input end voltage and EN enable end is normal. Then check feedback pin FB end
voltage and it is low obviously and EN enable end has false welding. After welding again, trouble is
removed.
[ Example 7 ] Symptom: machine down when playing MP4.
Description: machine down when playing video files.
Analysis and troubleshooting: firstly confirm whether machine is normal when playing Mp3. If it is
normal, we can decide power supply, reset and oscillation are normal. Check data and image processing
IC and we preliminarily judge that it is not related to image processing but related to data and address.
Picture information buffers and it is mainly processed through U1. Test power supply 3.3V voltage of U1
and it is normal. Change SDRAM directly and trouble is removed.
- 31 -
