I picked up a broken TV from a colleague the other day as he was glad to have it removed from his house. It’s a big one: 60” wide, with a fully functional screen. When powered on the screen stayed black and the power LED started blinking, suggesting a problem with the power supply. This was a great opportunity to practice my repair skills.
So when I opened it up it I immediately laid my eye on the blown capacitor: “BINGO!”.
I removed the board from the tv, desoldered the capacitor and soldered a new one back on. Without any hesitation I screwed the board back up on the TV and powered it on… At this moment I learned an important lesson: Think it trough! How could I possibly have thought it was that easy?
A blown capacitor means that something in this circuit has caused it to blow, therefore the capacitor is not the cause of the problem but merely a result. I realized I needed to learn more about power supply circuits and how to effectively trouble shoot them.
I took my time to do some reading into Switch Mode Power Supplies, and learned that the blown capacitor was part of a circuit called the ‘power factor correction circuit’. I tested all of the components belonging to this circuit with a multimeter (FLUKE 117) and a cheap Chinese multi-function tester. In order to test some of the components properly, they had to be desoldered from the board. Eventually I found out that the circuit contained a faulty MOSFET and a faulty diode.
To remove the MOSFET I had to desolder an entire heatsink containing 2 other MOSFET’s. Some of their pins got damaged while doing that so they needed a replacement as well.
After replacing these components, I screwed the power supply back on the TV and plugged all of the cables back on the board. I powered it on and it worked! Which makes this my first successful lucrative repair project.