So I turned the TV on the other day to watch something – all good – walked away, came back and the TV was off. Hmm, strange, so I tried to turn it back on but nothing. The next day I pulled the back cover off to find two boards, one full of SMD parts (for the video logic) and the other full of large high voltage parts (the power supply). I tested the fuse and it was blown so I swapped that for a new fuse. I plugged it back in and was greeted with a flash of light. I decided to dig a bit deeper and found the neutral and hot lines to be shorted somewhere. There weren’t any visible shorts on the board so it must be a component. I pulled the bridge rectifier off and the short still remained.
If you are familiar with switching power supplies then you know that the AC power first travels through a filter (consisting of inductors and/or capacitors) then it gets rectified to DC and filtered by a large capacitor. After that the DC meets the switching element, which usually consists of a MOSFET which then connects to a transformer. The MOSFET is the heart of the switching mode power supply and they usually have the supporting oscillator and comparator circuits built in to make them a complete SMPS package. These packages are sometimes hard to find when replacing failed components and if you can find them, they usually aren’t cheap.
About this time I started looking online for replacement power supply boards and to my surprise I found no less than 10 from various sellers. Either this board fails very often or they were simply pulled from broken TVs during recycling. In either case, I ordered one and 3 days later I had it installed and the TV working again. The best part was that the replacement board (with free shipping) was less than $15 and saved me from buying a new TV.