29 January 2012

TV Repair Bleg

I'm not a hardware guy.  I haven't done any work with actual, made-from-atoms circuits since my logic design class about a decade ago. And even then, we were just plugging things into a bread board, not working with production-level stuff. (Although we did build a calculator from scratch which could handle addition, subtraction and multiplication, which I think is pretty neat.)

Anyway, I now find myself trying to diagnosis a real piece of hardware, specifically the power supply to my old television. I have — I think — three blown out capacitors. That's what these look like to me, anyway.



One of them has leaked into whatever component that black and yellow boxy thing in the bottom photo is. The sticker on it identifies it as a BCK-25-1611/ROH, but I can't figure out what that is.

I'd like to be able to get this thing back in working order, for my own pride more than actually needing the TV.  Unfortunately I'm not really sure where to start. Where do I even buy replacement capacitors? Everywhere online I've come across wants to sell them to me in thousand-piece lots.

The leaky buggers are soldered into the board. Once I get replacements, do I just cut the old ones off? Then solder new ones in place?

And will that mysterious BCK-25-1611/ROH need to be replaced as well?

Anyone have any ideas about this sort of thing who can point me in the right direction?

I could get a whole new power supply, but the vendors seem a little dodgy.  And besides, where's the fun and accomplishment in that?

12 comments:

  1. I think you do cut the old ones off, and solder the new ones on. Try Radio Shack; it used to be the case you could buy all kinds of electronics components there in small quantities. Don't know if that's still the case, though.

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  2. Try http://www.digikey.com/
    You can usually get what you want in small quantities (if you know what you're looking for).

    If you can read what's written on the capacitor, I might be able to find the right one. A sharper picture would help too.

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  3. Radio Shack is so obvious. I should have thought of that.

    Sorry for the poor picture quality. All I had to hand is my phone, which isn't exactly set-up for macro photography, especially in the poor evening light in my apartment. I'll see if I can get a better shot tomorrow.

    Best I can tell the labels on the capacitors read "250V 47nJ" though the last letter might be "I"

    Thanks to both of you for the help.

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  4. Your mysterious box looks like a transformer. I would think the last two characters from the capacitors would be nf as in nanoFarad.

    They make a de-soldering gun. It's a soldering iron where the tip is a tube and there's a bulb on it to suck up the molten solder.

    Also good low volume suppliers:
    http://www.mouser.com/
    http://www.jameco.com/

    I would be curious why all three of those capacitors would fail. Can't point you in any direction but I would keep that in mind.

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  5. Yeah, that boxy thing looks like a transformer or a choke.

    Those caps don't look like the leakin' kind to me. The ones that usually leak are in the form of cylinders, usually with an aluminum can covered in a plastic label.

    Are you sure the material isn't an insulator/adhesive? Is it liquid and goopy or hard and solid?

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  6. I'll admit I'm guessing on the leakiness. This whole repair got kicked off because the TV was doing odd things for the first 20-30 minutes of operation. The screen would divide itself into three horizontal bands, with white lines of noise between them, and each band flickering up and down, then the lower right quarter of the screen would slowly fade to white, then the whoel screen would flash white, then the bands would bounce around some, and on and on until the whole thing finally warmed up.

    The best diagnosis I could find for this on a message board said to look out for some bad capacitors. I opened the thing up and all the cylindrical capacitors looked okay, then I noticed these three disc-shaped capacitors had that white stuff on them while many others didn't. So I just assumed that's what was going on. Plus one of the possibly leaky ones looks a little cracked, so I'm assuming this isn't just an insulator or glue or something.

    The white stuff is firm and slightly gummy. Not fully solid, but stiffer than "goopy."

    I have a theory about why three capacitors would all go bad, but I'm shooting in the dark here as well. There was a period of time when the TV would switch off momentarily whenever the heater in the room first came on. I was thinking the power disruption must have fried the capacitors.

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  7. Capacitors go bad.

    My guitar amp died a few months ago.

    There's a search engine specifically for electronic components http://octopart.com/

    Go there, search, buy.

    Consider getting a solder sucker as well.

    Don't cut the caps off ; heat the solder that holds them down, and then pull the caps out once the solder is liquid.

    Then heat the solder again and suck it out of the through-holes (aka "vias").

    Then replace with new caps.

    Note that many capacitors have a chirality. Resistors can go in either way, but caps can't. Get it right or you may very well blow up your caps once you power up.

    ObDisclaimer: I'm the proverbial software engineer with a soldering iron that the joke's punchline warned you about.

    Good luck!

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    Replies
    1. Thanks for the tips on both octopart.com and the procedure. I'll give this a go in the next week or two. I've already replaced the TV at this point, so I've got nothing to loose but a few bucks for replacement parts.

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  8. Sorry dude, but those caps aren't leaking - it's adhesive/insulator. A blown cap will be scorched - either brown/black and it will probably smell bad. The number you mentioned is 47nF (nanoFarad).

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    Replies
    1. This was my thought. Also: Only 'lytics leak; mostly only 'lytics go bad.

      Is this a TV with a vacuum tube display?
      We had a Sony Trinitron back in the 80's that had a problem like this. Tried to get it fixed; repair guy said there was a bad trace on the circuit board which he tried to fix. Worked for a while, then went back to the weird warm-up behavior. TV worked for many years after developing this problem, fwiw.

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    2. Why would only these three out of a couple dozen capacitors be glued down/insulated?

      Yes, it really does seem like they should read "nF" but I promise you they do not. Based on reading between the lines of some online parts catalogs it seems one particular manufacturer may labels theirs differently.

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    3. PS This is a two or three year old machine. It wasn't particularly state-of-the-art even then, but it's still an LCD model.

      I was willing to put up with some weird behavior on warm-up for a while, but it's getting progressively worse. By the time I finally benched it, it was taking over half an hour to settle down, which seemed exceedingly long time to warm up. But it didn't display the slightest symptom after that initial period.

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