TCL 75R615 has sound, no backlight

[thetonywarren]

Have had this TV since June 2019, worked fine till today. Daughter was watching it and made a noise and went dark. I unplugged, left off then powered back on, no change. You can see the image with flashlight test, but has high pitched noise/whine and no backlight whatsoever......I also tried a factory reset with the reset button on the back. Any ideas where I should start troubleshooting? Im pretty good with soldering iron and multimeter, but I dont have any documentation on this TV so I dont know where to start.

[dskall]

I would start at power board. Sounds like shorted component causing the led driver to make noise. Need some pictures of boards.

[thetonywarren]

So, I got some help yesterday to take the TV off the wall and got the back off to check out the boards....I did find a capacitor that was blown out,looks to be C312 a ceramic disc capacitor, very small and challenging to read, but was able to with a magnifying glass.....it seems to be a 220pf 1kv, I ordered some new ones from digi-key. A couple of questions, I dont notice with this type of capacitor that there is any polarity that needs to be observed? I have replaced numerous electrolytic caps and they have obvious polarity markings on the circuit board as well as the cap itself. Please see the attached pictures of the part number of the panel as well as some pictures of the internal boards, please offer up any help if you can....Thanks.

[dskall]

No polarity on those. Does it measure as shorted?

[thetonywarren]

I just checked the component via continuity test and it is shorted.

[lotas]

This is a high-voltage ceramic capacitor, they have no polarity, you can safely install it as you like.

[dskall]

You can probably remove it and see if everything powers up. Just read my disclaimer first.

[thetonywarren]

I think I'll wait till I receive the new component, before I power it back up....

[R_J]

I would remove the disc cap and check it out of circuit, I would also check the mosfet QW301 & QW302. I usually replace these 1kv caps with a 2kv

[thetonywarren]

When you say take the disc cap out of circuit, I'm assuming you mean the one that blew up and not another one near it or a different one? I did desolder it took it out of circuit and it tested shorted out ....I'll also check the two MOSFETs like you suggested......crap, I already bought the 1kv version instead of the 2kv like you said.....

[dskall]

I'm surprised you had video.

[R_J]

The 1k will be fine if that is what you ordered.

[R_J]

Originally Posted by dskall

I'm surprised you had video.

It seems to be the PFC circuit that has the shorted cap. The main board, t-con etc. likely operated and gave video but the led circuit needed the higher voltage and current to operate.

[dskall]

Thanks again for the info. I get on here mostly to learn. Do you know what happened to budm? Looks to be about a year since he posted.

[thetonywarren]

QW301 & QW302, as far as testing them....can they be tested in circuit, or do they need to be removed to be tested, I just want to make sure I do it the correct way.....im sure I can google a testing procedure, but I want to do it the quickest, most correct way....

Please let me know and thanks again for everyones help with this, it is much appreciated.....

[lotas]

You can check without soldering them, their legs should not be short-circuited with each other, this capacitor is parallel to the diodes.

[thetonywarren]

Ok, I'll test them later on this afternoon and post results on the mosfets....

[thetonywarren]

I tested both QW301 & QW302 in circuit and they are testing open across all legs.....I'm assuming per previous post that this means they are most likely good....

[dskall]

Well they shouldn't test open. Probably not testing them right, but they almost always test shorted if bad.

[thetonywarren]

Ok, does anyone have a good source for how I should be testing these particular mosfets? Ive viewed a few videos on youtube, but just looking for suggestions.....

Thanks!