**Solution Method:** After replacing with the same model D1504, the fault was eliminated.
**Analysis and Maintenance:** First, the output voltages of each group in the power supply circuit were tested and found to be normal. Generally, faults in the field protection circuit occur more frequently, so this part was checked as a priority. In the field protection circuit of this unit, Q1501 and Q1503 are sequentially turned on during the first half and second half of a field scan cycle. Since the voltage across C1511 and C1512 cannot change suddenly, the Zener diode D1504 is not broken down, and at this time, the protection circuit does not activate. However, when there is a fault in the field scanning loop, both Q1501 and Q1503 are fully cut off simultaneously, causing the Zener diode D1504 to break down, and the field protection circuit begins its protective function. Upon inspection, it was found that both Q1501 and Q1503 were normal, but further checks revealed that the Zener diode D1504 had already broken down.
**Fault Phenomenon:** For the Sony KV-L34MF1 TV, after turning on, the audio functioned normally, but there was a horizontal bright line in the middle of the screen.
**Data Source:** Beijing Sony TV Repair Phone: http://blog.sina.com.cn/sonydianshi
**Sony KV-L34MF1 TV:** Zener Diode Breakdown