Tv repair and oscilloscopes

[slag]

I recently picked up a 64 inch Samsung plasma that wouldn't turn on. P.O said he was watching a game and the TV made a popping sound and went out. I bought it for $100 and after bringing it home, opened it up. It was immaculate inside and out, came with the remote which he had never used as he had a harmony remote, and the mount/stand which was still wrapped in plastic as he had it mounted to his wall in his man cave. I replaced the fuse and it blew again. Researched it a bit on badcaps and on youtube and found the Mosfets (metal oxide semiconductor, field effect transistors) in a few places tend to blow. I purchased a few off digikey along with some new fuses and replaced them. The fuse no longer blows, but where I'm supposed to get 400 volts on the board, I'm only getting 160 volts. In my case, it doesn't appear to be a cap issue, but an issue in the circuitry that converts the incoming AC voltage to 400 volts DC. I believe its in the integrated circuits as I've tested the diodes, surface mount resistors, and capacitors.

So, I bought a replacement board on ebay for $130, put it in, and the TV works great now and is mounted over my mantle. But, I want to learn how to properly diagnose the problem and be able to fix these things instead of just solder on new parts someone else has found to be bad or replace boards.

With that in mind, I picked up a tektronix 422 oscilloscope locally. Appears to turn on and work well, and I've downloaded the manual. My dad used to use one when he repaired computers back in the 70s and 80s and is familiar with it, but I want to learn how to use it and be able to diagnose and troubleshoot problems.

Anyone on here have words of wisdom?

 

[Mr Evil]

The first thing I would do when trying to fix a PSU would be to identify the controller chip, then obtain the datasheet for it. From that, and from tracing the connections on the actual PCB, you should be able to draw a schematic, and work out roughly what voltages and waveforms you should expect at each node. Compare those expectations with the measurements from your multimeter and/or oscilloscope.

You're going to have to be careful with a 400V supply. Aside from the health risks, a quick Google for the manual for your 'scope says it has a max. input voltage of 300V.

 

[JackMDS]

Oscilloscopes where extremely useful ((I worked for many years with variety of Tektronix Osc.) when Electronics circuits were based on individual components that were relatively easy to replace (Transistors, resistors capacitors etc.)

They are still very important today in Scientific research and special systems.

In consumer electronic (like computers etc.) that are based on Modular electronics they are that useful since it is less expensive to replace a suspect module than to spend hours of paid salary to technicians investigate and trying to do manual repair of modules. In most of the time it not even possible to replace individual components on the Module.