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Electrical engineering questions

edited September 2011 in Technology
I rescued an HDTV a few days ago and have been trying to repair it. While it turns on, it goes to standby after between thirty seconds and three minutes.
Turning it back on again causes it to do the same thing but in only a few seconds, which lead me to think the problem is heat related.

The heatsink on it's processor seemed to have partially peeled off (It looked like a piece of metal tape folded over.) so I replaced it with some GPU RAM heatsinks but this didn't fix things.

I'm now looking at the PSU which is buzzing slightly, trying to find the culprit (I'm trying putting my ear against a very dry bottle and pressing the end against components in the hope that the buzzing component will transmit sound through the bottle.).
My current reasoning is the PSU is cutting out, but, as the power switch circuit is still engaged, it comes straight back to standby.

Any ideas which component causes this kind of fault? The buzzing seems to be coming from the top right of the PSU board. I'd have suspected the capacitor, but that seems to be glued to the board, so it wouldn't vibrate.

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Comments

  • Google brand name of TV and "heat"?

    Seriously though, we had a dodgy DVR that was having heat problems and after long and arduous googeling I finally managed to track the problem down to a ¢15 thingamajig on the circuit board that should have been a ¢50 thingamajig unless you want the DVR to fail after a year or so. The guy who tracked the issue down was an electrical engineer who designed similar DVR circuit boards.
  • Been googling plenty, I found someone on Ebay selling the CMI board (Top right.) and I've messaged him to see whether he has the PSU board.
  • Any ideas which component causes this kind of fault? The buzzing seems to be coming from the top right of the PSU board. I'd have suspected the capacitor, but that seems to be glued to the board, so it wouldn't vibrate.
    It's probably the transformer.
  • It was coming from that area and things involving electromagnetic induction tend to get hot. The problem now is knowing if something buzzing is reason enough to suspect it of cutting the power.

    Hopefully this guy will have the whole PSU board, which will mean just unplugging and screwing without need for soldering.
  • edited September 2011
    I've given it another listen and it's really not that loud. The hum coming from the flourecents is louder.

    I'm stumped for now. I'll work it out in time.

    One paper listening trumpet later and it's definitely the top right transformer making the buzzing noise.
    Post edited by Omnutia on
  • If googling isn't getting you anywhere get a volt-ohm meter, find the service manual for your TV online and start checking that things are at correct voltages. Start with power lines then +- lines on the chips. If you cant find a service manual test the power outs on the PSU they should be fairly standard voltages such as +-12 +-5. Black is almost always ground, Red is often 5, yellow 12. Also checking voltages on the caps themselves will likely get you nowhere w/ a voltmeter.
    Transformers especially tend to buzz, as can capacitors and thats not particularly unusual.
    If you have some components getting particularly warm look up the serial number on it for it's operating temp. Chips and transformers can get reasonably hot, capacitors generally shouldn't unless they're high voltage even then they shouldn't be more than warm to the touch.
    Beyond that check for solder breaks or melts. A decent multimeter should be able to do a continuity test. On a break often just reheating it will fix the problem.
  • edited September 2011
    Ordered a capacitance tester. It'll take a few weeks to get here.
    Going to have to look into where to buy capacitors.

    When I say I rescued the TV, I literally found it face down in someone's garden. They'd thrown it out when they moved.
    Post edited by Omnutia on
  • When I say I rescued the TV, I literally found it face down in someone's garden. They'd thrown it out when they moved.
    Aw yeah Headingly Style.
  • Ordered a capacitance tester. It'll take a few weeks to get here.
    Going to have to look into where to buy capacitors.
    Find a local electronic parts shop (not radio shack). A good one wont have a significant markup, and a few dollars for shipping on a $0.50 cap is silly.
  • Now that I've ordered the tester, I realise it would be quicker just to replace all the capacitors on the PSU than wait for the tester to arrive. I'll have to detach and resolder each capacitor in order to test it anyway.
  • edited October 2011
    I've de-soldered the cappacitors and I'm replacing all of them. Tester worked but it seems it's prolonged use that causes the blip in power.

    The titles are chopped off, It's placement --> Capacity in uF and Voltage in V.
    image

    My problem is C853 (160V 1uF); I've bought all the others but I can't find a radial capacitor that fits it's specs without ordering from the US. Can I use a ceramic capacitor or do they behave differently?

    Also, what's good for removing rust from circuit boards?
    Post edited by Omnutia on
  • Turns out I can use a 200V 1uF capacitor instead.
  • Turns out I can use a 200V 1uF capacitor instead.
    Yes, voltage mostly only matters in so far as it is above your max operating voltage. Also you can use a ceramic capacitor, or any other capacitor with the same values. The one big thing is that you cannot switch a electrolytic (polarized) cap for a non-electrolytic cap. Basically if a cap has +/- marks make sure the replacement does too, and vice versa.
  • OK, so this is a STUPIDLY basic question but I need some resources and have to start from somewhere:

    I have a replacement light switch to install. The current one looks like a standard wall switch dealie.. it's in a little metal box, etc. I can post pictures if anyone wants them.

    The one I want to install is a "deep socket" switch. Basically a rocker switch with some stuff over it.

    What should I know going into this? Since my arm is currently all tingly I realized quickly that I will need to turn the power off prior.
  • Perfect. Thank you, you probably saved me a heart attack.
  • Perfect. Thank you, you probably saved my life.
  • edited October 2011
    Perfect. Thank you, you probably saved me a heart attack.
    If you need me to do a Google/YouTube search for you, then you'll probably win a Darwin award very soon anyway.
    Post edited by Apreche on
  • If you need me to do a Google/YouTube search for you, then you'll probably win a Darwin award very soon anyway.
    HA, after I'd asked I found a couple of videos on my own. However, the one you found was a little better than the ones I'd found.
  • HA, after I'd asked I found a couple of videos on my own. However, the one you found was a little better than the ones I'd found.
    It was the top result on YouTube when I searched for "how to replace a light switch."
  • edited October 2011
    It was the top result on YouTube when I searched for "how to replace a light switch."
    ...good for you? I did a straight Google search and grabbed a random video, which ended up being about 2 minutes long and didn't help too terribly much. Then I decided to hold off since it looks like I'll need to do a bit more surgery to make the new switch fit, and I'll have to map out the circuit breaker a bit better. Your video was far more helpful.

    EDIT: more detail, less snark. I do appreciate the help.
    Post edited by SquadronROE on
  • Got a pair of these:

    Essentially three sets of headphones in one housing. The rear left speaker is no longer responding, I took them apart and it seems the problem is a break in the wire somewhere according to the multimeter.

    I'm suspecting the jack is the culprit, what are other people's experiences with headphones breaking?
  • I'm suspecting the jack is the culprit, what are other people's experiences with headphones breaking?
    Easily 90% of the time it's the cable, either where it connects to the jack, or connects to the headphone itself. The Jack itself is usually rock solid - not a lot that can go wrong there, honestly - but where it connects is a common failure point.

  • edited December 2011
    I'm suspecting the jack is the culprit, what are other people's experiences with headphones breaking?
    Easily 90% of the time it's the cable, either where it connects to the jack, or connects to the headphone itself. The Jack itself is usually rock solid - not a lot that can go wrong there, honestly - but where it connects is a common failure point.
    Most likely so. One way to check (poorly) without stripping the shrink tubing is run your fingers along the wire and at a break there may be a slight bulge. but yeah, in order of likely hood if there's a connectivity issue I'd put it at the body of the wire,connection to headphone housing, connection to any inline amps, and least the connection to the jack. Also a break at the jack would be pretty obvious if the headphones aren't complete shit.

    Post edited by Shiam on
  • Most of the time with those type of headphones the break is at the flexible part of the jack and where it meets the headphones. I ended up just replacing the whole cord instead of splicing it.
  • edited February 2012
    Alright again fellaz, here's 25mb of photo's of the offending jack. I can't see anything wrong with it but I'm very tempted to take the cutters to it.

    It's the middle one. Do people still think it's the most likely break point? Problem is the three cables fuse into one shortly there after so once cut, there's not a huge amount to work with.
    Post edited by Omnutia on
  • edited August 2012
    Back with another question. I'm using my RS-120s which are wireless, AAA battery powered and still holding up ok after many years of use.
    One problem I find with them is that any sudden loud sounds or really bassy noises cause the volume to drop for a short time and then fade back up.

    This has only become a regular problem with the shotgun in BF3 which sounds like a beast but drops the volume for a split second each time it's fired.

    So, would putting a capacitor in-line with the batteries allow for the sudden power drain without causing the volume to drop out?

    I'm going to go remind myself how amps relate to farads.

    The bad news: AAA batteries can have varying discharge rates.
    Good news: There is probably a capacitor already in there I can swap out for one with a greater capacity.
    Post edited by Omnutia on
  • any sudden loud sounds or really bassy noises cause the volume to drop for a short time and then fade back up.
    That sounds like a limiter in the base-station, not a power issue.

  • edited August 2012
    If I could find a way to give the headphones a better power supply, I could rule it out.
    The batteries seem wired in series so a 2.4v current but I can't work out the power draw as the drain isn't constant. I've seen it at 100mA idle.

    For future reference:
    image

    Another thought I've had is using this video with full and mostly empty batteries to see if it's taking it's time to come back depending on available charge.
    Post edited by Omnutia on
  • Non-sequitur: I've come to love plastidip for all my insulatory needs. Who needs heat shrink tubing anyway (;
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