### Fault Symptoms:
Automatic shutdown.
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### Fault-Related Circuit:
Field output circuit.
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### Fault Location:
External capacitor C520 connected to Pin 12 of LA7837 has broken down.
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### Methods, Techniques, and Tips:
Checkpoints for determining whether the CPU protection circuit of Haier TC-2139 TV is activated.
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### Analysis and Troubleshooting:
The voltage at Pin 41 (protection detection input) of CPU N801 was measured as 2V (normal value should be 5V), confirming that the protection circuit had been triggered. After disconnecting jumper wire W654, the voltage at Pin 41 of CPU N801 returned to 5V. By sequentially disconnecting each protection diode, when the field power protection diode VD643 was disconnected, a horizontal bright line appeared on the screen upon turning on the TV.
After powering off, the resistance between each pin of the field output integrated circuit N501 (LA7837) and ground was checked, revealing a short circuit at Pin 12 of N501. Further inspection of the peripheral circuitry around Pin 12 found that capacitor C520 had broken down. After replacing C520 with a new one (0.1F/100V), the entire unit returned to normal operation.
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### Case Reference:
Haier TV Beijing after-sales service center, September 23, 2011.
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### Conclusion:
Automatic shutdown issue resolved for Haier TC-2139 TV.