Technical data for Beijing Hisense TV repair hotline.
Analysis and Repair: Measuring with a multimeter, the +B output voltage is around 50V with a fluctuating needle. The power supply voltage of pin 12 of the CPU N901 (M50436-560S) is also fluctuating at about 24V. Then, the secondary power supply was measured to be fluctuating between 2.4V. In standby mode, the +B voltage is only 27V but still able to output 7.6V as the secondary power supply. Now that the +B voltage is around 50V, it should also be able to output 7.6V. However, the secondary power supply is too low and unstable, which suggests that the secondary power supply's voltage stabilizing circuit might be faulty. Practical testing revealed that the negative terminal voltage of VD834 is 0V. After turning off the power and measuring VD834, it was found to be broken down. Further inspection showed that the forward and reverse resistances between each pin of V831 are not conductive. After replacing VD834 and V831, the fault was resolved.
★When the +B output voltage is around 50V, the breakdown of VD834 often accompanies a cold solder joint on its positive terminal, because the positive terminal of VD834 is close to the edge of the circuit board, making it prone to poor contact. When replacing components, the negative terminal can still be soldered in the original place, while the positive terminal can be rewired to an adjacent pin marked GND, thus avoiding the above phenomenon.
Hisense TC-2130BCBK TV shows no signs of life upon startup, with the indicator light flashing
Fault Symptoms: No raster, no sound, no image, the power indicator light flashes, and the +B voltage is low.
Fault-related Circuit: Power Supply Circuit
Fault Location: VD834 breakdown, V831 open circuit
Methods, Techniques, and Tips: Excluding common faults of low +B voltage in Hisense TC-2130BC/BK TVs.