Bad capacitors in newish LCD TV

[JohnR66]

My parents have a 52" Samsung LCD TV that they bought in 2008. It stopped turning on. It would keep trying to turn on but would just cycle. Opening the back and looking at the PSU board, I see two electrolytic capacitors with swollen tops that have leaked. I went home and returned with my soldering gear and capacitors that I happen to have the right values in stock. After replacement, TV is fine again.

I'm disappointed to see this problem persist as the bad capacitor issue started 10 or more years ago. My computer power supply quit for the same reason.

TV PSU board.

 

[cryhavok]

Nice work. This is actually a very common problem with LCD TVs...there are tons of posts on tv forums about this exact problem.

 

[kingofwylietx]

Good find, you certainly saved them some money.

 

[Lynx_Arc]

I would replace all the caps that size on that board if it were me.

 

[jtr1962]

If you can find solid polymer caps with the same uF and voltage rating then that would be the best choice for replacement. If not, go with the highest temperature and ripple current electrolytics you can find.

 

[HarryN]

I am still always amazed that people keep making new designs with through hole components. Of course, this made it possible for you to repair the problem.

JTR1962 is right though - the solid polymer caps are usually more reliable, although if you don't get a high enough voltage rating, they have their own "interesting" characteristics.

It might be interesting to open up those blown caps. I saw a picture on-line of a cap that had been opened, and it actually contained within it a lower rated cap. (counterfeit part).

 

[Illum]

SMTs have limitations in capacity...to a certain point the mechanical integrity of through hole caps is still preferred, especially for HV caps.

Besides, it helps to have a clean, isolated board for easy inspections. Though the downside of Thru-Hole is the size of the board, but in the new LCD TVs, space isn't that big of a concern unless they're going for the ultra thin designs.

 

[louie]

Samsung TVs in particular are having this problem, and it's widely reported. Samsung seems to be covering repairs even if you are out of warranty.

I figure bad caps will continue to be a problem as long as manufacturers seek cheaper parts, and cannot verify what corners the suppliers have cut. Myself, I stocked up on caps from Mouser for my 2009 Samsung!

 

[alpg88]

wow, good post, i have 50" plasma samsung that i bought in pbly 2007 or so. still works fine.
now i know what to look for, if it starts acting up.

 

[PhotonWrangler]

Great catch, JohnR! Those caps might have failed from poor materials or they might be overstressed from either heat, higher-than-rated voltage across them, or both.

We had a device at work that had lots of bypass electrolytics on the motherboard, and the designer chose a 16v capacitor for a 15v power bus! Needless to say, the slightest surge would push the caps over the edge, and 'sploded capacitors were a regular event until we started replacing them with a higher voltage rating. I think the rule of thumb is to derate them by at least 3:1, so a capacitor placed across a 10v bus should be rated for at least 30vdc. This increases the physical size of the capacitor so there is a high limit to wvdc ratings.

 

[JohnR66]

That board is so sparse because it is all surface mount on the opposite side. I see a lot of boards designed this way now. Even my "old school" cassette recorder I bought at Rat Shack a couple years ago is like that.

I replaced the 25v caps with 35v Xicon brand of the same capacitance. Xicon is one of the brands not affected by the "bad cap" issue (AFAIK). It is really the only part I had. I didn't have the right values to replace the other ones, but they didn't look swelled at all. According to my meter, the bad capacitors had a bit less than half their value remaining and probably much higher impedance.

I'll have to get the model number and check their 42" Samsung plasma to see if it has a history.

My computer became the same way. It became harder to get it to turn on and finally wouldn't turn on at all. Several caps on the low voltage side had swelled tops and seeping electrolyte. In this case, I bought a new PSU. I keep watch over the motherboard. So far so good. It is a computer I built in 2004. No money in the till to upgrade.