Fixing a Samsung TV

Last year my cousin and his family were due to head down the New Forest for a holiday, but unfortunately had to abandon that plan after numerous electrical items in their house packed in within a few weeks of each other. This sounded highly suspect, and could have been due to dodgy wiring or the generally poor filtering of the mains supply in their area at the time. One of the things to go was their TV, which apparently "made a pop, then wouldn't turn back on".

As the TV was replaced with a newer, larger, thinner, and altogether more shiny one, the old was was for the bin - naturally I offered to attempt a repair, or if I couldn't do anything for it, at least save them a trip to the tip with it.

Fast forward to the Christmas holidays when I finally was in the right end of the country to pick up the offending item, and I found myself in possession of a deceased Samsung LE32B450 LCD TV.

First I checked that it was indeed totally dead (and not just a fused plug), and used a different mains cable - no luck. Time to open her up then.

As you can see below, there is a lot of empty space behind the main panel.
On the left we have the input and output sockets, including HDMI, audio, etc... whilst on the right we have the power supply. The input is via the black female socket at the bottom, with power to the main electronics going via the black ribbon cable at the top. Also of note is the power to the backlight, which goes straight from the power supply PCB via small tabs (just above visible along the edge in the photo below)

The insides of the TV

Of note I saw that there was a fuse next to the power lead socket, and I confirmed this had indeed blown. Replacing it with a common 5 amp plug fuse (not the right type, but good enough to see if it made any difference) it was clear something else had gone too - out with the multimeter!

There are not a lot of accessible test points on this side of the PCB, but I saw a bridge rectifier at the bottom of the heatsink that runs top-to-bottom along the board as it offered an easy way to get my probes connected, and sadly there seemed to be no electricity present there.

Scouting the internet I saw that a number of Samsung TVs had issues with bad capacitors, so I gave them - along with every other component on the top side of the board, a good looking over for visible signs of distress, but everything seemed to be in order. No sign yet of whatever made the smell, and potentially let the magic smoke out. Time to unscrew the power supply PCB and see what it looks like underneath...

The underside... Showing some suspicious burn marks

Ahar! Not quite a smoking gun. but clearly this part of the circuit had done some smoking at some point, with the underside of the bridge rectifier component showing serious signs of having blown up.
The multimeter confirmed that serious damage had been done, and 3 of the 4 joints were no-longer making electrical contact.

The offending part

 The rectifier is a GBU406, a fairly standard part capable of tolerating 600V on the input - which means there must have been some serious power spike to blow it, or melt the solder.

[N.B. It is possible that this component still works, I haven't tested it, but I wasn't keen to resolder it in place given what it had been through.]

I ordered a new one off eBay - £1.35.

The replacement

The good news was the new one looked identical to the old one, so I went about unsoldering the dud so I could pop in the fresh one.

Old one unsoldered

New one in place

It's not immediately visible from these pictures, but the old part ripped off some of the PCB traces when it popped, so there wasn't a lot to solder back onto. Therefore I made extra makeshift pads by scraping away the green protective coating and lacquer to reveal some the the PCB trace below, and soldered to that too.
I confirmed that everything was not electrically connected to adjacent components, and then set about testing the power supply board again

Testing

Now, it's very important that you know what you are doing when there is mains voltage about. I have a healthy fear about touching things, so I kept my distance and was careful where I poked my multimeter probes. Please don't do this unless you know what you are doing and have taken appropriate precautions.

Upon inspection I was now getting voltage out of the rectifier and off towards the rest of the board. As I didn't really know where to test for correct voltages (or what those voltages might be), I decided here goes nothing, lets just put it back in the TV. Also, as nothing else seemed obviously in need of replacement, I'm not sure what my next plan of attack would have been, so decided just to go with it

This looks promising!

She Lives!

Well, would you look at that!

The only thing left to do is replace the fuse with one of the correct rating, and it'll be good to go once more - and my cousin will have a second TV that he will need to find a home for...