caps outy of spec are they good?

[odgaf]

i got an lg tv that i inherited broken, got it home turned on but you could only watch 1 channel, any attempt to change channel or enter a menu caussed tv to turn off then wouldnt turn on again for a while, i removed powerboard took some measurements put the supply back in and it worked perfectly for a few months,, now you turn it on backlight comes up and it turns off just before picture, occasionally it will turn on and work perfect till you turn it off,
i whipped off the powerboard again and started checking caps, i found 2 10volt 3300uf in parallel which i removed, they both have low esr but are showing up as high 3770uf and 3760uf, are these caps bad?

[stj]

Re: caps outy of spec are they good?

probably high electrical leakage.
i would replace them.

[odgaf]

Re: caps outy of spec are they good?

thx for answering, ive ordered those 2 caps but now tv is working again ...., seems whenever the powerboard is removed overnight the tv comes good ?

[stj]

Re: caps outy of spec are they good?

then look real close at the soldering for fine cracks - specially on larger parts or parts bolted to heatsinks.

[odgaf]

Re: caps outy of spec are they good?

firing up the iron right now

[momaka]

Re: caps outy of spec are they good?

i whipped off the powerboard again and started checking caps, i found 2 10volt 3300uf in parallel which i removed, they both have low esr but are showing up as high 3770uf and 3760uf, are these caps bad?

Not necessarily.
Electrolytic capacitors typically have a tolerance of +/- 20%. So for a 3300 uF capacitor, the capacitance can be as low as 2640 uF and as high as 3960 uF with the cap still considered "in spec".

That said, when you start seeing the capacitance higher than 10% of nominal value, this *could be* an early indication that the capacitor's Aluminum oxide layer is starting to break down. This means the capacitor *could be* becoming electrically "leaky", as stj said. Basically, the leakage current through the cap is higher than before, meaning the cap self-discharges faster. This fools your meter into showing higher capacitance.