Common issue with Samsung BN44-00213A

[Dannyx]

Good day folks. I thought I'd share my findings on what I consider the most common failure on these BN44 supplies. In my case, it's a 00213A, though it may apply to other boards in the BN44 family.

The issue is as follows: the owner would hear a pop and see some smoke coming out of the cabinet followed by the obligatory jump-scare They'd bring it in, I'd take it apart...the fuse is blown on the thing and no caps appear to be failing, so now I'm pretty stumped and start measuring semiconductors thinking one of them has gone kaboom, but no luck. Now as I'm doing this and flipping the board around, I suddenly notice a massive burn mark hiding behind the main reservoir cap and NOW I see what the cause of failure was: blown snubber cap (CM801 in this case)...seems I run into this issue a lot with PSUs lately, more so than regular electrolytic cap failure, go figure :| The jumpers are also fried, so it looks like we have to rebuild those as well...great...soldering iron, plenty of solder, melt, suck, repeat for the other leg and the snubber's out. Repeat for the jumpers (or what's left of them). Clean the area as good as possible. Fabricate some new jumpers out of the thickest solid-core wire that could still fit in the holes...ok, they look a bit wonky, but they do the job Install a new snubber of the same value of course (22 nF-222 printed on it) but with one voltage step higher than the original (2kV instead of 1kV). Put new 6.3A fuse in. Light bulb test tells us we're safe. Put the PSU back on the chassis and try it out. Job done

[tom66]

Re: Common issue with Samsung BN44-00213A

The snubber is under a lot of dv/dt stress so failures definitely can happen. Unusual otherwise for those types of caps to fail. One other thing to look for is that awful brown/beige glue. It can go conductive with age, and could cause a similar fault, especially given its location on the cap.

[Dannyx]

Re: Common issue with Samsung BN44-00213A

The snubber is under a lot of dv/dt stress so failures definitely can happen. Unusual otherwise for those types of caps to fail. One other thing to look for is that awful brown/beige glue. It can go conductive with age, and could cause a similar fault, especially given its location on the cap.

Call me clueless, but what is dv/dt ? I can't say I'm very familiar with electronics theory in general - I'm more of a practical guy and know the basics of how some components work, I don't know the "numbers" going behind them

[tom66]

Re: Common issue with Samsung BN44-00213A

Call me clueless, but what is dv/dt ? I can't say I'm very familiar with electronics theory in general - I'm more of a practical guy and know the basics of how some components work, I don't know the "numbers" going behind them

Voltage change (dv) over time change (dt)

If you remember your calculus it's a differential equation but that doesn't really matter all that much.

Essentially the parts of a capacitor aren't uniform. You can think of the 220pF capacitor as being composed of a large number of parallel capacitors say a pF each or so.

Recalling some basic electronics theory will tell you that current through a capacitor is proportional to change in voltage (I = C dv/dt). The problem is if dv/dt is very high, then it leads to a very large "I" through very small "C". These capacitance "units" are randomly distributed in many capacitors, so there are some parts that have more capacitance...some less. This leads to some areas heating up more than others, which can cause thermal expansion, damage, arcing or other types of failure. And failure can be progressive, developing over time, or instantaneous.

[Peterg251]

Re: Common issue with Samsung BN44-00213A

Guys, Thank you for the good info. I came home from a week away, the house empty, to find the lounge telly dead. A quick inspection found the board fuse blown but the caps OK. New fuse saw the thermister blow and plug fuse as well. Still no definite cause seen, New plug fuse saw 2.2nf cap blow and then saw this post, confirmation of suspicions!! Ebay purchase of parts, 2 days, fitted this am, SUCCESS!! No signs of shorts in glue but, I suspect low voltage testing might miss a high voltage breakdown when set is under load. Cleaned all the glue off in the key areas anyway to be safe.

TV fixed for a fiver, that is the first modern TV I have fixed that had a real fault and not just bad caps, the only set not gone wrong yet (commentators curse) is the oldest Samsung (12 years and counting). Glad I signed up.