The resistance is a very common component when our family master repairs electrical appliances. In the past, when repairing CRT color TVs, the damage of the resistors generally showed that the resistance value became larger or open. For example, the starting R of the power supply part, the load resistance of the C pole of the discharge pipe, the sampling resistance of the color line ABL, and the like. However, in the maintenance of LCD TVs, I found that there are many examples of the resistance of the resistors becoming smaller! The following is an example of a small resistance value, write it out and share it with you.
Renovated a Changhong iTV32830EX color TV, and there was no sound after the second boot. Disassemble the machine and check that the BL-ON/OFF pin voltage of the constant current board socket is 0V after the second power-on. The BL-ON/OFF ground resistance is not short-circuited. It is proved that the BL-ON/OFF branch of the main board JUC7.820.00033862 is faulty. After researching the motherboard, it was found that BL-ON/OFF is controlled by the N-pole transistor Q3 and the C-pole of the screen printing H1A, and the b-pole of Q3 always has a voltage of 0.68V after the second power-on, so the Q3 is saturated and the C-pole outputs a low level. So the constant current plate does not work.
Short-circuit the foot of Q3, the backlight is normally lit, and the image appears. Prove that Q3 and constant current board and LED strips are normal! Followed by the b pole of Q3, it was quickly found that the external pull-up resistor R4944K7 of the BL-ON/OFF pin of the main chip was reduced to several hundred ohms! After replacing the R494, the test machine is OK. Thanks for watching!
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