Baking Electronics 101: oven reflow on a TV logic board

A while back, Mae got a used 32″ LCD tv for her birthday from our friend Max. I mounted it on the wall in the work-out area of the garage and we both use it to watch tv while working out.

A couple days ago, I was working in the garage for a few hours and had the tv on in the background, and I didn’t notice when but at some point the screen went black. The sound continued working fine, which is probably why I didn’t notice it.

I spent a while fiddling with it, turning it on and off, checking the inputs, changing channels, etc. The sound kept working fine, but no display, although I realized that there was a gray haze that came over the screen when I turned the power on. That led me to believe that the backlight was still working, but something wrong with the video processing.

I hit my friend Max up. He had told me a while back that he used to fix busted tvs (in fact I think he had fixed this one up), so I asked what I should do next on it. He told me to examine the logic board and look for a bad capacitor.

I took down the tv from its wall mount and removed the back. Examining the components on the board, I couldn’t find any that looked damaged or burned out.

Max then reminded me of the oven reflow trick. He had used this to successfully bring a Macbook back to life… for a while. The idea is that over time, due to heat and other conditions, one of the solder points degrades and eventually fails to conduct. Heating up the board can reflow the remaining solder and restore the connection. At this point, I had nothing to lose…. if the reflow trick didn’t work, I would just throw the tv away and buy a new one, so it was worth a try.

I unscrewed the board and removed the connections, then placed the board on a cookie sheet covered in aluminum foil.

I’d like to say I used some mathematical formula to arrive at how hot the oven should be and for how long the board should be in the oven….but I winged it. I set the oven to 375F and once it pre-heated, I put the board in and left it for about 8 minutes or so. This was just long enough to get a good whiff of plastic heating up. I took out the board and let it cool for about 15 minutes.

I didn’t have a ton of hope that the tv would work again, but I had come this far, so I put the board back in place and replaced the connections. I powered the tv back on and…. like Lazarus emerging from the tomb, the image sprang to life! The oven reflow had worked!

Which solder point had flaked off? How long will it continue to work? Who knows! Maybe I bought myself another year before I have to replace the tv.

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