Replacing a bad cap on TV

[justjoe]

I have a 39" LCD TV which has a screen fading problem and using a cheap multimeter ive been able to test half the capacitors and found 1 is bad and figure its worth trying to replace it being so cheap, but the cap is a Samxon 10uF 50v km(m) b4a, thats all the info written on it, and ive been told they are an average brand and sometimes very poor depending on the spec.

I wanted to ask if its ok to use say Rubycon or Panasonic, and if so how do I make sure I get the exact right spec, or even better could someone point me to an example of an alternative.

Ive never done anything like this before but im very keen to learn about it, always been interested in electrics and regret not taking a course when i left school.

Thanks for your advice.

[Pentium4]

Re: Replacing a bad cap on TV

Of course Rubycon or Panasonic would be a good replacement, I usually use Panasonic FC series for small caps because they are high quality and cheap. How did you determine that the cap is bad, is the capacitance really low on it or is it shorted?

[justjoe]

Re: Replacing a bad cap on TV

Of course Rubycon or Panasonic would be a good replacement, I usually use Panasonic FC series for small caps because they are high quality and cheap. How did you determine that the cap is bad, is the capacitance really low on it or is it shorted?

Interesting thanks, so it sounds like the series determines the quality, I always wondered about that.

Yes the capacitance is low, its reading 3.7uf instead of 10uf, the other caps im able to test all give a healthy reading so im hoping this cap is the only bad one.

Another question I have is about buying an ESR meter, I see the price range is either very low or very high, can I get away with a cheap one? do I really need to spend big money for simply testing caps? because this very cheap multimeter seems to be good enough for the smaller caps.

[Pentium4]

Re: Replacing a bad cap on TV

I have a Peak ESR70 (the ESR60 might be cheaper and pretty much the same thing) Capacitance/ESR meter, it should be easy to get there in the UK. All Panasonic caps are very high quality. Low ESR isn't very important with caps like that one that has such a low capacitance

[justjoe]

Re: Replacing a bad cap on TV

I have a Peak ESR70 (the ESR60 might be cheaper and pretty much the same thing) Capacitance/ESR meter, it should be easy to get there in the UK. All Panasonic caps are very high quality. Low ESR isn't very important with caps like that one that has such a low capacitance

wow £100 i was looking at one for £15 lol

glad you said that about ESR, ive just read about how important it is but the datasheet for this cap doesn't mention anything about ESR. Im going to order the same cap and hope it works and the only bad one then try a better brand if that one goes bad again, being new to this im best playing it safe I guess.

Thanks for your quick replies guys its been very helpful.

[Pentium4]

Re: Replacing a bad cap on TV

Oh :/ haha... yeah hopefully it's just that cap!

[justjoe]

Re: Replacing a bad cap on TV

Oh :/ haha... yeah hopefully it's just that cap!

I tested the cap about 10 times over 3 days and always got 3.7uf maximum, but now ive removed the cap its reading a healthy 10uf as it should, it seems strange i should get a bad reading so many times, is that normal or is it possible the heat from the solder and pulling it out has somehow fixed it?

[Pentium4]

Re: Replacing a bad cap on TV

I think it's better to test them out of circuit it gives the most accurate reading, it's rare that a cap with such low capacitance goes bad, only 10uF cap I've seen go bad was CapXon and Fuhjyyu. Have you tried soldering it back in to see if it works now?

[truep]

Re: Replacing a bad cap on TV

Look on Ebay for an ESR meter. I just bought one that tests the value and the esr of the cap, as well as diodes and transistirs. It cost around $20-50 USD (depending on which seller. It doesn't haxe a case but that's no problem for me. I did install soft plastic stick on pads to keep it from sliding around. It dorsn' have instructions either but will test caps between TP1-TP2 ,1-3, 2-3. It autodetects the part being tested.

[tom66]

Re: Replacing a bad cap on TV

Screen fading problem?
Backlight fades or what?
Have you checked the power supply outputs?

It might not be a problem with the power supply at all.

[justjoe]

Re: Replacing a bad cap on TV

I think it's better to test them out of circuit it gives the most accurate reading, it's rare that a cap with such low capacitance goes bad, only 10uF cap I've seen go bad was CapXon and Fuhjyyu. Have you tried soldering it back in to see if it works now?

No not yet but im about to try it, but im not confident, theres so many components i cant believe ive been that lucky now with this cheap meter.

[justjoe]

Re: Replacing a bad cap on TV

Look on Ebay for an ESR meter. I just bought one that tests the value and the esr of the cap, as well as diodes and transistirs. It cost around $20-50 USD (depending on which seller. It doesn't haxe a case but that's no problem for me. I did install soft plastic stick on pads to keep it from sliding around. It dorsn' have instructions either but will test caps between TP1-TP2 ,1-3, 2-3. It autodetects the part being tested.

Yea thanks, I was looking at that last night and £50 seemed a good price to start me off.

[justjoe]

Re: Replacing a bad cap on TV

Screen fading problem?
Backlight fades or what?
Have you checked the power supply outputs?

It might not be a problem with the power supply at all.

Yes the backlight works ok, never had problems with it, but the actual picture would flicker to a darker picture but then eventually fade away, then i press the brighter menu button and the text tries to appear but fades out again very slowly. Now i get no picture at all just a backlight, and i can hear the channel so i still get sound ok.

I dont know how to check the power supply outputs no, maybe i should upload a photo so you can see the boards and wires?

[tom66]

Re: Replacing a bad cap on TV

That sounds more like an LCD tab bonding problem. You can attempt to verify if the PSU is at fault by measuring the supply rails. If they're dropping, it's likely at fault, but if they're more or less steady, then it's unlikely.

[justjoe]

Re: Replacing a bad cap on TV

Ok i'll go do that then lol just kidding, ive got no idea what any of that means but im gonna go google lcd tab and supply rails and find out but first im gonna solder this cap back on and ive got a lot of other reading to do yet, so much to learn man, thanks for your help guys.

[tom66]

Re: Replacing a bad cap on TV

Do you have a digital multimeter?
Black probe on metal chassis.
Meter on DC200V or DCV. (Must be a digital meter.)
Red probe on the exposed metal around each pin leaving the power supply.

[justjoe]

Re: Replacing a bad cap on TV

Some photos to show you the cap I suspected.

[justjoe]

Re: Replacing a bad cap on TV

Do you have a digital multimeter?
Black probe on metal chassis.
Meter on DC200V or DCV. (Must be a digital meter.)
Red probe on the exposed metal around each pin leaving the power supply.

This is the meter, my bro gave it me when he gave up his car audio repair business but i dont think its good enough for the job after coming here and learning about ESR meters.

So is this a digital multimeter? obviously if not then i dont want to risk doing what you just said yet.

[tom66]

Re: Replacing a bad cap on TV

Nothing wrong with that, perfectly adequate for most repairs. TBH most caps bulge when they fail. 95% of them do. However, there's no point shotgunning caps if you don't even know if the PSU is at fault.

For measurements, set the range switch one step left, to the "V=" position.

[tom66]

Re: Replacing a bad cap on TV

Can we get a close up of this sticker too? We can perhaps look up the panel datasheet from it.