42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

[ComputerGeek]

Hey Everyone, So I have another Free Pickup from our local Dump, This time it was a 42" Sylvania 6842pe m LCD TV. And I need a little help, Once I got it home I plugged it in, pressed the power button, and I instantly got a sound that something was shorting out. So I went around the back and listened for the approximate location of the sound. Next Pulled off all the covers and I looked in the general location of the sound. And not long after found a Blue tantalum Cap burnt to a crisp with one half of it missing. Next I located datasheets and traced the Cap number c2250 to be a CERAMIC CAP. B K 1500pF/1KV.

Can any tell me what the B K in this stands for? "CERAMIC CAP. B K 1500pF/1KV"

I am assuming that the Cap just didn't go bad by itself knowing that these caps usually don't fail. Where Should I start looking for Bad Components? The Diode next to it is a SCHOTTKY BARRIER DIODE YG123S15 how do I test this?

Finally, all the Caps on this board are Nichicon either GN or VZ series should I worry about replacing any of them?

Thanks!

[budm]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

Ceramic cap failure mode is shorted circuit, when it goes bad, it is shorted out. That cap can be part of the snubber circuits to reduce the kickback spike in the primary side of the switching power supply transformer, there should be Diode and resistor in that area. We need to see the pictures of that area of the board, pictures of both sides of the board.

[ComputerGeek]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

Hey Everyone, So I have another Free Pickup from our local Dump, This time it was a 42" Sylvania 6842pe m LCD TV. And I need a little help, Once I got it home I plugged it in, pressed the power button, and I instantly got a sound that something was shorting out. So I went around the back and listened for the approximate location of the sound. Next Pulled off all the covers and I looked in the general location of the sound. And not long after found a Blue tantalum Cap burnt to a crisp with one half of it missing. Next I located datasheets and traced the Cap number c2250 to be a CERAMIC CAP. B K 1500pF/1KV.

Can any tell me what the B K in this stands for? "CERAMIC CAP. B K 1500pF/1KV"

I am assuming that the Cap just didn't go bad by itself knowing that these caps usually don't fail. Where Should I start looking for Bad Components? The Diode next to it is a SCHOTTKY BARRIER DIODE YG123S15 how do I test this?

Finally, all the Caps on this board are Nichicon either GN or VZ series should I worry about replacing any of them?

Thanks!

Sorry I must have been up too late here are photos and the datasheet. Thanks!

[ComputerGeek]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

Sorry About the one Photo being Rotated.

[budm]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

OK that is the snubber cap ( that cap is in series with the resistor next to it), this RC (Resistor-Capacitor) is in parallel with the rectifier diode (to reduce the diode switching noise) that is mounted on the heat sink. You need to check out thr resistor and the diode to make sure they are not damaged.

[ComputerGeek]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

OK that is the snubber cap ( that cap is in series with the resistor next to it), this RC (Resistor-Capacitor) is in parallel with the rectifier diode (to reduce the diode switching noise) that is mounted on the heat sink. You need to check out thr resistor and the diode to make sure they are not damaged.

Yes How I test and tell if the diode is Good? I have the diode test setting on my meter. Do I just test it one way then reverse the leads? Do I have to test lead to heatsink too? What values mean that a diode is good?

I really want do know if you know of a guide for testing different semiconductors. So I can see if something is shorted without having to ask you guys about every step. Do you know of anything like that? I can do resistors and some of the other components fine? I am just unsure of the values to expect when testing Semiconductors?

Any help Would be great!

[budm]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

The Diode as shown in the picture is only a single Diode in TO-220 case, so just set the meter to diode mode and measure the two legs. Good diode will show reading one way only, it should show 0.4~0.6V on your meter, then switch the test probe, then it should show OL, or 1 depends on your meter.

[ComputerGeek]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

Ceramic cap failure mode is shorted circuit, when it goes bad, it is shorted out. That cap can be part of the snubber circuits to reduce the kickback spike in the primary side of the switching power supply transformer, there should be Diode and resistor in that area. We need to see the pictures of that area of the board, pictures of both sides of the board.

Here you were saying that Ceramic Caps usually only fail in a shorted circuit. What is the difference between ceramic and Tandelum? I thought that bule caps are Tandelum is that not correct?

The Diode as shown in the picture is only a single Diode in TO-220 case, so just set the meter to diode mode and measure the two legs. Good diode will show reading one way only, it should show 0.4~0.6V on your meter, then switch the test probe, then it should show OL, or 1 depends on your meter.

OK diode tested to be 1 one way, and the other way there is a quick beep then the meter went to 483, on the diode test setting. Also, correct me if i'm wrong but doesn't a diode test show ohms not volts?

The Cap reads open in its current state so it is not shorting.

The resistor Between the Caps I believe this is the one you meant, reads 10.12k ohms. Location R2252 METAL OXIDE FILM RES. 3W J 47k Ω test in Circuit should I pull and Retest?

Thanks!

[budm]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

That is Ceramic cap. Tantalum also fail shorted circuit.
My Fluke meter in Diode mode will show x.xxx V on the screen showing the forward voltage of the semiconductor. Looks like your Diode is OK.
If it reads 10K and it is labeled with 47K (47K is about the right value for the R/C snubber). The power supply should still function with the burnt cap removed, most cheaply made TV do not put any snubber circuits at all. Yes remove lift one leg of the resistor and read its value.

[ComputerGeek]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

OK I am heating up my iron to desolder now, what else should I check? How do you tell a Ceramic from a Tantalum? If I follow you right Ceramic caps don't really fail unless there's a short.

So If I just pull that Cap the Tv should work fine? Should I do this? Do you think only the Cap went bad?

"If it reads 10K and it is labeled with 47K" what were you saying here then it bad?

[ComputerGeek]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

It's not the resistor its 46.7k when Pulled.

[budm]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

The ceramic when it goes bad and break down, it will short itself up. I do not believe they make Tatalum cap in disk form.
Yes, that reading of the resistor is bad, it should be 47K, you need to check with one leg lifted off the board. I looked at the bottom side of the board, this resistor is not part of the snubber circuit, it is a voltage bleeding resistor to discharge those two black caps.
The blue cap is connected in parallel with the rectifier diode.
You can leave the resistor as is for now, and you can remove the cap to see if the TV will power up OK.
One thing I see on the bottom side of the board is some kind of corrosion in picture #4 around bottom left of the board, take a good look at it

[ComputerGeek]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

OK Let me try that, The resistor was 46.7k when Pulled so its fine.

That is left over flux they never cleaned,soldering quality so-so.

[budm]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

I think the reason you were reading 10K because it is in parallel with the load (the circuits) that the two caps and the resistor are connected to, you are OK with the resistor. I just took me a while to trace the connection from the pictures.

[ComputerGeek]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

Ok Pulled the Cap and It starts right up I have done any other testing but I will. So if I replace that one component I should be Good? Any Clue as to what made it Fry?

Is there anything else I should do when I am in here? Tv is 6 years old.

Hopefully I'll get a couple bucks for it to add to my collage fund.

[ComputerGeek]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

c2250 to be a CERAMIC CAP. B K 1500pF/1KV.

Can any tell me what the B K in this stands for? "CERAMIC CAP. B K 1500pF/1KV"

Finally, all the Caps on this board are Nichicon either GN or VZ series should I worry about replacing any of them?

And I Am still interested to see if and of you know of a guide for testing different semiconductors. So I can see if something is shorted without having to ask you guys about every step. Do you know of anything like that? I can do resistors and some of the other components fine? I am just unsure of the values to expect when testing Semiconductors?

[budm]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

I have no idea what the 'BK' stands for. You got that from the service manual?
I just Google "how to test transistor and diode"
Example:
http://www.repairfaq.org/sam/semitest.htm
http://www.mikroe.com/old/books/keu/11.htm

[ComputerGeek]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

So one of these will work fine. http://www.digikey.com/product-detai...PH-ND/2356798?

So if I replace that one component I should be Good? Any Clue as to what made it Fry?

Is there anything else I should do when I am in here? Tv is 6 years old. All the Caps on this board though are Nichicon either GN or VZ series should I worry about replacing any of them?

[budm]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

That is correct voltage and value. Parts do breakdown, especially the high voltage parts, Ceramic cap can easily be cracked since it is just a Ceramic disc, so be real careful when handle them.
Nichicon are good caps, after 6 years they may be due for replacing, you can replace them all but will it be worth the time and money for Sylvania?

[ComputerGeek]

Re: 42" Sylvania 6842pe m LCD TV Won't Power Up/Shorting Noise?

Yeah Idk I was going to try to get $200 for it, do you think that is too much?

I had the TV running without that cap from 8:30AM to 12:30 at Night without any problems. However, there is noticeable noise coming from the power supply. Almost like a gringing or a low Hum I am wondering if the Caps going bad might be causing this. It changes depending on the Picture on the Screen, if the screen is black then it makes no or very little noise, If is bright it is a lot louder.

Could the other caps going bad possibly have caused the snubber cap to blow?