Sunday, February 26, 2012

Home TV Repair, Part III

Back from the store, I spread out newspaper on the dining room table and plugged in the soldering iron.  The first step was "tinning" the tip of the iron, which means melting a bit of solder onto the tip and coating it with solder.  This keeps the tip from rusting and makes it easier to solder.

Next, I took a look at the power supply board, flipping it front to back until I could determine which solder points on the back side were the ones belonging to the two bad capacitors.  I marked the points with a sharpie pen, then laid down the board upside-down.

Now it was time to do a little de-soldering, something I hadn't tried in decades, and never on an electronics board.

I can tell you the little de-soldering bulb, well, sucks.  You use the iron to heat up and melt the existing solder, in your other hand squeeze the bulb, place the bulb tip as close to the melted solder as possible - even touching - then quickly release the bulb so it will slurp up the old solder.

Okay, it wasn't really the bulb's fault. :) I was having trouble keeping my hand steady while rapidly releasing the bulb.  I did finally get the solder slurped up, but it took some practice.

If I ever have to do this again, I think I'll try a "vacuum desoldering tool," which is basically a spring-loaded solder sucker.  You cock it, point it at the solder to be removed, and press the trigger.  Bingo!  Solder gone.

With the solder gone, I turned the board over and removed the two bad capacitors.  And I was lucky -- sure enough, the two old capacitors were 1000 microfarads each, just like the ones I had bought.  But there were two differences:
  1. The old capacitors were 25-volt; the new ones 35-volt, and slightly larger in diameter.
  2. The old capacitors were black, and had a higher heat rating, good to 105 centigrade.  I didn't recall seeing anything like that in stock at the electronics store.  The ones I bought were blue, and rated to 85 centigrade.
From everything I could gather, replacing the old capacitors with higher voltage ones was not a bad thing -- perhaps superior to the originals.  I was concerned about the heat rating, but finally rationalized it to myself that perhaps a higher voltage/slightly bigger capacitor would not run as hot as the old ones.  Besides, I didn't want to have to special order capacitors off the Internet and wait days for delivery.  So, right or wrong, I installed the capacitors I had.

This is where I expect to hear from someone who knows this stuff.

Putting in new capacitors is just a matter of sticking the wires through the holes, then bending them in opposite directions to hold the capacitors seated in place.  The important part is to make sure you put them in the right way:  positive wire through the positive hole; negative wire in the negative hole.  Both capacitors and the board are marked.

Once in place, just turn the board over, and you can solder the capacitors.  With the iron, touch the wire at the board, wait a couple of seconds, then touch the solder to the hot wire.  The solder should melt pretty quickly, filling the hole.

It only takes a very small amount of solder.  In fact, I overdid the first one with a large blob, then used less solder for the remaining holes.  After inspecting my work, I decided I needed to redo the first over-sized blob for fear it might make contact with something nearby.  I de-soldered it, and tried again, and got looking like the other solder points.

After that, it's matter of clipping the excess wire from the capacitors, and reinstalling the power supply board.

After putting everything back together, with much anticipation of smoke and fireworks, I plugged the TV back in.  Nothing bad happened.  I picked up the remote control and hit the power button.  The TV turned on normally!  Yeah, my home repair worked!!!

At this point, my only lingering concern is the heat rating on the capacitors.  Did I do the equivalent of replacing a flat tire with space-saver tire?  Something that will work for the time being, but really should be replaced?

Well, at least I know I can replace capacitors successfully.  If the TV breaks down again, I'll buy the right temperature-rated capacitors for the next round.  As I now own a soldering kit, that makes the next repair even cheaper; just the cost of the capacitors themselves, about $4 or so.

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