Today, I was called to repair a Skyworth 21N16AA TV that the user reported had a "squeaky" and "noisy" sound. Upon opening the case, there were no obvious signs of burning on the high-voltage pack or the high-voltage cap. Based on my past experience with this model, I suspected an issue related to the voltage rise. To confirm whether the increased sparking voltage was due to the B+ voltage, I used a short-circuit line to drive the transformer's secondary winding and performed a dummy load test. The B+ voltage rose to 200V. If you have some repair experience, you can immediately tell which component is causing the problem.
I removed capacitor C610 and tested its capacitance. After replacing it, the B+ voltage dropped to around 85V. But was there another faulty part in the power supply? I carefully examined the power supply section and noticed that it had been previously repaired. The sampling potentiometer had been turned all the way counterclockwise, and it was centered. When I disconnected the dummy load and reconnected the short-circuit line, the image lines appeared jagged on both sides, but the B+ voltage didn’t improve much. At this point, I thought the previous repair might have missed something, and another component could be at fault.
I removed the two suspected components for inspection. One showed signs of having failed, leaving a visible scar, while the other, C610, looked good. I replaced both with new capacitors rated at 160V/100μF. The TV powered up without any fire, which was a good sign.
Capacitors C610, C615, and C616 are commonly faulty in this type of circuit. It’s possible that during the previous repair, C610 wasn’t fully replaced, leading to incomplete restoration. Adjusting the sampling potentiometer to lower the B+ voltage may have caused instability in the filtering system. This kind of issue is quite common, and the resulting overheating or fire can often be traced back to a faulty B+ filter capacitor. For beginners, it's important to pay close attention to these components when diagnosing similar problems.
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