3.3.1 Servicing cases
[ Example 1 ] Symptom: power not on.
Description: no OSD and no output.
Analysis and troubleshooting: firstly confirm whether it is caused by battery or power circuit.
Connect with computer and check whether display screen has display. Power on, connect and there is
no display. Take the player apart and check. Firstly test power supply voltage and it cannot be lower than
3.2V. Use multimeter to test between anode and cathode of battery and then check VCC3.3V and 1.8V
that output through BGA. During the checking, we find that 3.3V is normal and 1.8V is normal. When
pressing ON button in normal working, after testing actually, VCC1.8V should be pulled down to about
1.7V, which is normal. When working normally, VCC3.3V should be slightly lower to 3.1--3.2V, which is
normal. Then test crystal oscillator X1 and oscillation is normal. The frequency is 12MHZ and it is
11.999MHZ after testing actually. Reset is also normal, so we finally judge that main decode chip has
trouble. Change chip Rk2608 and upgrade software again. Power on and trouble is removed.
[ Example 2 ] Symptom: power not on.
Description: no OSD and no output.
Analysis and troubleshooting: firstly confirm whether it is caused by battery or power circuit.
Connect with power adapter and check whether charge is available and whether screen has display.
After power on and connecting, there is no display. After taking machine apart, firstly test power supply
3.3V and 1.8V and we find 3.3V is normal. Then test 1.8V and voltage on two ends of L13 and find that
1.8V only has 0.7V. Observe DC-DC switch IC U6 carefully and find that pin 4 feedback has rosin joint.
After welding again, trouble is removed.
[ Example 3 ] Symptom: machine not power on.
Description: after pressing ON button, screen has no display and headphone has no output.
Analysis and troubleshooting: connect Mp4 player with computer and there is no display. Test
charge current and find that current is large. Open machine casing to test and current is normal. Power
on again and it is normal, so we preliminarily judge that short-circuit in a certain position causes the
trouble. Observe carefully and find that two lead wires of buzzer have been damaged to cause the inner
part show outside and short-circuit with bottom casing, which makes working current of the player large.
After installing battery, machine cannot power on. Change buzzer lead wire, test and trouble is removed.
Section Three Servicing Cases
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