Possible leaked cap ? ? ?

Thread Starter

Tonyr1084

Joined Sep 24, 2015
3,676
Have a Toshiba 50" flat screen LCD TV. Quit working. At power-up you get a brief flash of light then all's dark. This TV was owned by my neighbor who reported the TV still receives and plays audio, but the screen is blank. There's not a whole lot to this TV. I'm wondering if the power supply board has failed (or partially failed).

I've pulled the power PCB off (and discharged the main capacitor). I'm seeing on the solder side (one sided board) what appears to be some white traces of something. The cap in question is a 56µF 100V electrolytic cap. The top side of the can does not show any distortion. Before I jump into "Replace And See" mode I wanted an opinion. Overall the board looks pretty darn clean, so to think this is flux residue seems a little questionable. Not impossible, but I'd tend to think it's not.

This cap is not on the power supply side of the board (large cap, BR, Chokes and fuse)(and other stuff). It may have something to do with powering the LED's. Given that you get about a tenth of a second flash of light then all goes dark - I'm wondering if the cap may be bad. No - I haven't pulled anything from the board yet. I'd like to get as good as possible an idea where the issue may lay before I start melting (RoHS) solder.

Leaked Cap.jpg
 
Last edited:

bwilliams60

Joined Nov 18, 2012
1,198
What is the model number of the TV? Did you check all of the power supply voltages? They are generally clearly marked beside the connector. Can you post up pictures of the back of the TV to show all the boards?
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
3,676
Yeah, I can. However, they're fairly large sized and I've had to crunch down the views of what I wanted to show. Let me get after the model number. There are two boards; one that receives 120 VAC, rectifies it (rectifier output is 167 VDC). Filter cap (470µF 220 VDC) holds charge (until discharged through resistor).

Will take a while to respond. Wife wants to dine out. Sorry - wife trumps hobby.

[edit] No, haven't checked those yet. The board is pretty scary and I don't want to probe something with my huge test leads and blow something out. Will have to see if I can get a plug that will fit and then just separate the wires and make connection to those. There's 5.1 and 12 volts. Assuming DC.
 

bwilliams60

Joined Nov 18, 2012
1,198
I'm going to say that if you are not familiar with these sets that you probably shouldn't go poking around in them. There are components in there that will lay you out as I am sure you are aware. I have been into many of these and although caps are sometimes a problem, they are not always the problem. Model number will tell me a lot more. Enjoy your fine dining.
 

SLK001

Joined Nov 29, 2011
1,533
Your TV has lost a back light LED or two. With everything still working, you should be able to see an image with a flashlight held at an angle. Major surgery - not difficult, but major surgery to replace. You have to remove all the patient's "organs" to get at the damaged "heart".

As for being "laid out", the only part that can bite you is the main PFC capacitor, which will hold about 320V DC for a while when turned off. Either avoid it, or discharge it with a 2k or so resistor. Even if you do nothing to it, the caps "bark" is worse than its "bite" (but you will feel it)!
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
3,676
Yesterday I took several photographs with my cell phone. Unfortunately the file sizes are too large to upload. I'll have to find an older camera with a lower pixel count to take the pictures again. @bwilliams60 I will get the model number for you. But being Halloween, I have some decorations to put up for tonight's chilly affair. Expected to be in the mid 30's this evening. Not expecting as many participants as this is the ninth coldest Halloween on record.

BOOOooooo.
 

bwilliams60

Joined Nov 18, 2012
1,198
Your TV has lost a back light LED or two. With everything still working, you should be able to see an image with a flashlight held at an angle. Major surgery - not difficult, but major surgery to replace. You have to remove all the patient's "organs" to get at the damaged "heart".

As for being "laid out", the only part that can bite you is the main PFC capacitor, which will hold about 320V DC for a while when turned off. Either avoid it, or discharge it with a 2k or so resistor. Even if you do nothing to it, the caps "bark" is worse than its "bite" (but you will feel it)!
Wow I didn't know that all LCD Tv's had LED backlighting so thanks for pointing that out for me. I also didn't know that 50" LCD TVs didn't have small transformers that help light up the TV screen and put out upwards of 700 volts which will lay you out. I must have been thinking of something else. My bad. I guess if I were working on a SMART TV like he mentioned, that the backlighting would be done by LEDs and they are very common and easy to replace. Thank you for straightening me out on that as well. I appreciate the lessons.

Tonyr1084, I hope you have a Happy Halloween and when you get the pictures up, we can help you out.
 

SLK001

Joined Nov 29, 2011
1,533
Wow I didn't know that all LCD Tv's had LED backlighting so thanks for pointing that out for me. I also didn't know that 50" LCD TVs didn't have small transformers that help light up the TV screen and put out upwards of 700 volts which will lay you out. I must have been thinking of something else. My bad. I guess if I were working on a SMART TV like he mentioned, that the backlighting would be done by LEDs and they are very common and easy to replace.

Thank you for straightening me out on that as well. I appreciate the lessons.
You're very welcome. Always glad to help the junior members out there.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
3,676
I may have said LCD and LED - honestly, the TV is what it is. Bottom line I get a moment's flash of light then black screen. Could be TFT for all I know. The TV was built in 2013. Whatever prevailing technology was then - - - .

I'm still trying to get some decent pictures, but so far everything has been very pixilated when cropped and zoomed in. Virtually no useful information other than there are two boards on the back of the TV.

Give me a few more minutes to pursue another attempt at taking some photo's. If I get something decent I'll crop it and post it. Otherwise I believe my picture files are oversized and won't fit on the forum. (gaud I love change). "(
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
3,676
OK, lets see if I can attach some photos:

Nope. The first one is too big - even after having cropped it down. Second one came. Third won't. Fourth won't. Says the file size is too large for the server. Is this something new?

The ONLY photo to attach is of the connector that goes inside the big tin box where the lights are and where the colorie thingies make pretty pictures. This is frustrating.
 

Attachments

SLK001

Joined Nov 29, 2011
1,533
The ONLY photo to attach is of the connector that goes inside the big tin box where the lights are and where the colorie thingies make pretty pictures. This is frustrating.
I see the problem... The plug that should plug into this connector is missing!

No, really, the FLASH at the very beginning was a self test failure. WHATEVER technology is in the big tin box MOST LIKELY has a failure condition, either a burned out CCFL or LED. The software is setup so that when a current or voltage is outside of a certain range, the display backlights will shut down. Some TVs will shut the entire TV down, while some will just shut off the BLs. It appears that your TV does the latter, which is why I suggested that you shine a flashlight at the screen to see if you can see images. To replace a BL is MAJOR SURGERY, because EVERYTHING has to be removed. It's not difficult, just fully document everything that you do, or even better, video tape all that you do. This will make putting everything back once surgery has completed rather easy. I say to video your steps, because once you get to the damaged part, you'll have to order the exact replacement, which can take a week or more.
 

Reloadron

Joined Jan 15, 2015
4,593
Following the flash something you can try is this. Take a flashlight and hold it at some various angles against the screen. Look at the screen at a few angles. Now do you see anything like a picture? When flat screen monitors first came out that was a common trick / test to see if the back light had failed. It should also work with a TV I think. Nothing to lose anyway.

Ron
 

MisterBill2

Joined Jan 23, 2018
4,061
There are still some of the sets that use florescent lights of some size for the backlight, and those DO have some higher voltages to supply them. Now with that white powder, I would clean it off a d re-solder the connections with GOOD TIN/LEAD SOLDER. Just remember to not eat that solder because eating it is unhealthy.
The LEDs are arranged in series strings and run on quite a few volts, but usually less than 100 volts. I recently dismantled a very large curved-screen set that had fallen onto the floor face down. It lit up but it had lots of cracks and only a small portion of the screen worked. The cost of repair was several hundred more than the cost of replace, and after dismantling it I understand that the LCD screen has two connections for every pixel, and while they are shared that is a lot of connections. But there should indeed be test points and they might actually have voltages marked on them.
 

bwilliams60

Joined Nov 18, 2012
1,198
Hey @Tonyr1084, now that I have seen the model number, I can agree with @SLK001 assessment. I would go into the LED strips and find the dud(s). It is a common problem but I still stick with what I said initially. There are some 50" TVs that pack a punch and can lay you out if you are not careful. throwing caution to the wind on a public forum is not my style. But I am just a "junior" member apparently so hey, what do I know :) Good luck with the repair. You got this.
 

MisterBill2

Joined Jan 23, 2018
4,061
There is a way to check LEDs in a series string that is totally safe and works well, but it is quite tedious. The special equipment needed is a fairly small adjustable regulated power supply that can be set to around 3.5 volts, or a bit less, and able to supply up to about 70 milliamps, max.Also two probes with fairly sharp points. The testing is done with the set power off and disconnected, so there is no shock hazard. The procedure is to apply the voltage to the LEDs one at a time, after first setting the supply to a voltage that will light the good LEDs to a medium intensity, which will be at a current of 20 to 50 mA. The failed LEDs will not light nearly as bright at that voltage, or will not light at all. Usually the voltage will be between 3.1 volts and 3.3 volts.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
3,676
Lots of good input. Thank you all.

Interesting thing about my friend (neighbor) - - - He can't wear wrist watches with batteries. The batteries die within a week. Even new batteries. At least that's what he tells me. He's had this TV for about 3 months. It's obviously a used TV but reports are that it was properly cared for.

Anyway, thanks for the advice. Especially the video taping thing. If it takes a few days to get something in - I'll probably forget what order things came off in.
 

MaxHeadRoom

Joined Jul 18, 2013
19,198
Lots of good input. Thank you all.

Interesting thing about my friend (neighbor) - - - He can't wear wrist watches with batteries. The batteries die within a week. Even new batteries. At least that's what he tells me.
It the watch analog style?
If so, tell him to go digital, I think my (digital) watch battery has been in there at least 8 - 10yrs!. :cool:
Max.
 
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