37-inch fake Samsung one machine more sick - appliance repair

Probe domestic switch needle KG-300K, with a head diameter of 3.0mm, is a normally open switch needle.

100V, 250mA, surface mount, high-speed switching diode.

TP-IP4220CZ6, 5V, 0.35PF, breakdown voltage 6V, SOT package.

Shunuo varistor / ESD varistor / complete product line / Sunlord first-class agent.

Photocoupler.

The V59 board screen shows T370HW V5. The initial fault was a grimace, followed by automatic shutdown. Then the green light turned red. The power board output for 5V and 12V was normal, but 24V was missing. The 24V is supplied by an independent switch transformer. The IC used is UC3842, and its 15V power supply is normal. After some time, the 24V returned to normal. The test machine still had issues, and after a few seconds, it showed the following image: The test machine briefly turned into a gray screen. Upon checking, the logic board’s fuse F1 was open, and Q302 was also damaged (U801 power supply). A 12V maintenance power supply was added to the logic board, and the current reached up to 800 mA. It was found that V20 and R205 were hot, and R205 had changed color, although the resistance was still normal. After removing V20 and powering on again, the current remained high. The hand felt heat from U21 (AS15-G), so it was replaced. After restoring V20 and replacing Q302 with a 0-ohm resistor (welded at the R332 position, which was empty), the test machine worked properly.