What is this component?

[ezenia]

I've recently got my hands on a broken TV and I'm looking to see if it's an easy fix or not.



The TV is currently not displaying any image on the screen. When I plug in the power cable, I get a red power LED, which I assume is the standby light. After holding the power button for a few seconds, it turns blue. The screen is unresponsive. The marked component in the image above is producing some sort of constant noise. It does this on standby mode and when it's on. When it's in standby, the sound is a lot quieter, you have to really put your ear real close to the component to detect any sort of audible tone. When I hold the power button and the light turns blue, the noise increases in volume. The noise isn't extremely loud, but can be heard if you're near the back of the TV, or close to the component itself. It's at its loudest when the power light is blue.

I'm just wondering what that marked component is on that power supply board and why it might be producing a constant noise. Does the fact it's making a noise explain why there is no image at all on screen? Is it likely to just be a power supply board issue, or could the issue be deeper than this?

Appreciate any input.

[ataradov]

That's a transformer and it is normal for it to produce noise, more under load.

And don't put your ears close to the power supply, it has live voltage on it.

If TV does anything at all, then it is likely not the power supply.

[ledtester]

Check if any external outputs of the TV are working. For instance, do you get any audio out of the external audio outputs?

A lot of LED TV problems are due to the LED backlight not working.

[PKTKS]

WILD  guess by just looking that... 

And that PFC guess may be a simple forward converter
as well.. that depends on the chip controller
which should be on the other side..


Paul

[ezenia]

So I've done some more testing based on information received. Here's what I found, whether it's any good I don't know.

This is the sound the marked component makes immediately maybe seconds after the power LED turns blue: https://vocaroo.com/1lRGnczyvSMA

Hopefully the audio recording makes the sound I'm hearing clear.



If I remove the cable that's marked, the sound I hear stops completely. Power LED is still solid blue.

The marked cable goes here:

Multi-meter reads 12V on both pins. The BK/ON pin seems to be giving different readings every time I touch the red probe on it. Sometimes it'll show about 0.770V and other times it'll show 0.500V or something lower. At one point, it was even reading 299.1mV or so and dropping. Not sure if this means anything. The ADJ pin seems to consistently read around -004.5mV or so. Both of the SGND pins seem to give similar readings to the ADJ pins.



The marked cable goes to the above area on the main board (the red-coloured cable).

I tried shining a backlight at the screen as I've seen in some videos. Nothing could be seen.

I ran something with audio on my laptop and connected it via HDMI to the TV. The sound cuts on my laptop (as expected) and I assume is supposed to be going to the TV. However, the TV does not produce any audio whatsoever.

Connecting an external USB speaker does not produce sound either. The speaker reacts to me plugging in the cable, but is not producing the sound playing on my laptop. If I remove the HDMI cable from the TV, the sound plays on my laptop once more. The laptop seems to detect that I am connecting it to a TV, but the TV is just not doing anything of value.

The power LED stays solid blue the entire time. There's no flickering. If I leave it unattended for a while, it'll go on standby (Red LED).

Anything else to try? Does this information help narrow down a possible cause? If it was a backlight/LED issue, shouldn't there be sound playing still?

[Manul]

Sound seems ok, do not worry about that. If power supply makes clicking sounds, then it might suggest that it is overloaded. Stable buzzing or whining sounds are normal.

Did you check all power supply voltages while on? 5V, 12V, etc? There are also local switching converters on the main board, like for example 3.3V. Are they all ok? You may try checking voltages on these SMD electrolytic capacitors. Be careful to not short something. Does something at all gets warm while it is running? That main IC with heatsink, others?

[ezenia]

Above is a screenshot of some measurements taken from the caps.

On the left side of the board, there's also a cap next to the heatsink. I got around 05.22V on that as well.

There's also a USB port that has a cap sitting next to it, that also reads around the 05.22V region.

I went into continuity mode and both sides of the cap beep.

I think there might be a short on the main board?

[Manul]

So did you check voltage of every capacitor which is visible? Basically just look for suspicious voltages. Standard voltages are like 24, 12, 5, 3.3, 1.8V, some big ICs like CPUs may use lower voltages like 1.2, 1V. If you see near zero, or some other odd voltages like 4.2 it should draw your attention.

Continuity mode in this case is a tricky thing, looks simple, but it is not. It measures resistance and beeps if it is lower then some 10's of Ohms. The result also depends on how much current the multimeter applies to make a measurment. High density boards offten have these low resistances measured on power rails, this is normal and does not necessarily mean it is shorted. If you power the board and you see normal voltage on the capacitor - it is not shorted.

I do not see very high hope for this TV, but sometimes failures are related to power problems and power is relatively easy to check. So check it good everywhere.

[ezenia]

Ah. I see my mistake. I think my multi-meter was set up wrong or something. I saw "05.22V" and thought that was suspicious as I was expecting to see "5.22V" or something like that. I will be re-checking tomorrow and probably should try touching some of the IC's to see if any are generating heat. That's how I've diagnosed some laptop boards as bad (one chip would always heat up immensely). I'll check for the same on this TV since it is actually powering on and the board does seem to be receiving the power based on some measurements taken so far.

I don't think there's anything wrong with the power supply board. I'm starting to suspect it's not that now. I should also check the smaller caps I can see. I was only checking the bigger circular caps.

[PKTKS]

Here is the thing which first comes to my  mind
on that kind of scenario.

My diagnostic steps follow the symptoms:
- noise? PWM is noisy by default and audible
  means it has gone hairy wild..
- why?  usually a single led or more failed
- how to check? several ways.. scope the best.

Your board seems to have all voltages in place
but kicks protection as soon as Blacklight command
trips in..

Scope will confirm that.. you will then proceed
to LED testing

Cheers
Paul

[ezenia]

I assume scoping the board requires some sort of special tool? If so, I don't have anything that can do that.

I also assume it's normal for the Novatek chip on the T-CON board to be getting a bit hot when it's powered on?

If it's the LED's, is that an issue inside the screen itself, or on one of the 3 boards (PSU, Main or T-CON)?

Could it be an issue with the GPU/CPU (whatever is under the heatsink)? I notice there's no heat at all on the heatsink or around the area.

[Manul]

I assume scoping the board requires some sort of special tool? If so, I don't have anything that can do that.

I also assume it's normal for the Novatek chip on the T-CON board to be getting a bit hot when it's powered on?

If it's the LED's, is that an issue inside the screen itself, or on one of the 3 boards (PSU, Main or T-CON)?

Could it be an issue with the GPU/CPU (whatever is under the heatsink)? I notice there's no heat at all on the heatsink or around the area.

He suggested to use oscilloscope to observe how the voltage changes.

What I tried to say earlier is to look for suspicious temperatures - something too hot or too cold. If that main heatsink is totally cold, that could be suspicious.

[ezenia]

Yes, the heatsink is totally cold. It doesn't feel like any heat is coming from it. The surrounding ICs around it are also not warm. I can't seem to find any other spots that are dangerously hot.

I put my multi-meter on the part of the cable that connects to the BK/ON pin and I got a reading of about 05.22V on both sides (power supply and main board). Does that mean the backlight is OK and the issue may be that the CPU/GPU is just not coming on, which is why there's no image or sound?

I also put my multi-meter on the LED+ cable and got a reading of 212.9V - is that right? That seems really high.

[Manul]

I don't know about LED voltages. Seems high, I would expect somewhere 50-100V. You should measure between LED+ and LED- while the LED cable is connected. If you disconnect the LEDs the voltage may be a lot higher.

By the way, is there no light at all? If you look in dark room you dont see any light coming from screen edges?

[ezenia]

I did the test with the LED cable plugged in. I had black probe on ground and red probe on the LED+ part of the cable. I did black on LED- and red on LED+ and got the same reading. It's a stable 212.9V reading.

And yes, there's no light at all. It's pitch black no matter where I look or what I shine at it.

I connected my laptop via HDMI, plugged something with sound and the laptop went quiet. However, the speakers were not making any sound whatsoever. Both internal and external speaker do not make any sound. I am assuming that since the laptop went quiet, it detected the TV and if there was sound, it should have been playing as it does on another TV I have.

It feels like this is a processor issue or something since the board does seem to be getting power. There's even a red light on one of the ports. I feel like the heatsink should at least be warm.

[ezenia]

Ok, so I ran the flashlight test once again. This time I got ready before I turned the TV on. I turned off all lights I could, put phone's flashlight on and aimed it at the TV. I then turned it on. Previously, I was just doing this test whilst the TV had been on for a while.

I found that I could see the "Bauhn" logo appear. It stayed for maybe 5-6 seconds (estimate) and then went off. Power LED is still solid blue.

I tried pressing the menu button and can see the menu appear under flashlight.

What does this mean?

[PKTKS]

(.))
I found that I could see the "Bauhn" logo appear. It stayed for maybe 5-6 seconds (estimate) and then went off. Power LED is still solid blue.

I tried pressing the menu button and can see the menu appear under flashlight.

What does this mean?

**IF  YOU CAN SEE IMAGE with a light underneath.. **
good news..

It means your main board is OK (as your voltage readings already shown)

but your backlight is bad.

First thing to do is get yourself the datasheet of the backlight
controller chip.

 2 possible scenarios:
= your LEDs  are bad and require replacement of some or entire strip
= THE OCP or OVP on the controller is firing...

both very common issues.  You are required to have skills
to determine these..  the first easiest is LED failure.

However been 50% inconclusive the testers are very helpful
because they can spot 50% of cases. TKDMR is a reputable brand

https://www.aliexpress.com/item/2020-TKDMR-NEW-LED-Tester-0-300V-Output-LED-TV-Backlight-Tester-Multipurpose-LED-Strips-Beads/4001155350991.html

The scope will show you the bad PWM driver been tripping the
protection which ** CAN BE ** tripped by a faulty component on
the detection network (sense resistors or mosfets)

That is better spotted with the schematics and the proper
voltage level of OVP or OCP  values...

SCOPE HELPS...  cheapest thing very handy for that huge panels
https://www.aliexpress.com/item/1005001370348106.html

Paul

[drussell]

Many LED-backlit LCDs use the LEDs all wired in series.  On those, that means that all you need to do is find the one dead LED (often you can see it by eye, will usually have an obvious black spot in the die area, otherwise just test them one by one with a multimeter on diode mod, for example, or other power source) and just bypass it, solder a jumper across it.

You'll never notice one LED missing behind the diffuser, and they're driven with constant-current anyway.  It usually takes longer to disassemble the silly panel that it does to find and bypass the blown LED.

[PKTKS]

Many LED-backlit LCDs use the LEDs all wired in series.  On those, that means that all you need to do is find the one dead LED (often you can see it by eye, will usually have an obvious black spot in the die area, otherwise just test them one by one with a multimeter on diode mod, for example, or other power source) and just bypass it, solder a jumper across it.

You'll never notice one LED missing behind the diffuser, and they're driven with constant-current anyway.  It usually takes longer to disassemble the silly panel that it does to find and bypass the blown LED.

90%   of models are really in series..  that is why you need
in some cases more than 300V DC tester...

But several models (cheapos) use  "series" strips with a multi
strip controller...    reason the controller datasheet is needed.

The OCP and OVP values are written in the datasheet and
need to be checked .. as a single led failure will trip OCP..

Paul

[Syntax Error]

Looking at the PSU board there is evidence if a lot of heat stress. Especially around the legs of the power transistor next to the word HOT. Some of those diodes look baked too.

Have you checked for dry joints with a magnifying glass? Mechanical temperature cycling can often break solder joints, especially on parts attached to a large heatsink. At a glance, these defects are not obvious. They can be fixed by just reflowing the solder.

[ezenia]

Ah, that's what I had feared (wouldn't be an easy fix).

Should I be getting sound though? I've looked at similar cases online of bad LEDs and they all report having audio.

For me, sound is dead as well it seems. I'm going to be checking for sound again today now that I know there's an image under flashlight. I'll be hooking up my laptop to see what it's doing.

I'm unfortunately not skilled enough to fix it if it looks like it's the LEDs. It looks like a nightmare to get access to the LEDs.

I was hoping for a simple board switcheroo, but that's looking more unlikely as time goes on.

[Manul]

I would say - don't worry about heat marks, at least yet. You have output voltages after all. What is strange is that you have LED voltage, but there is no backlight. Also voltage seems quite high which also indicates that the LEDs might be open / disconnected. On the other hand I would expect all else to work without backlight. So might be multiple failures present. Do these wires go directly to LEDs, or is there some additional controller in between?

For starters I would suggest to look, does 200V actually reach the LEDs. Maybe you fill find something and at least fix one fault.

[ezenia]

There is only one LED cable that connects to the power supply board and that cable goes somewhere into the panel. It looks like a nightmare to get to the LEDs, so I'm not keen on dismantling further to actually see the LEDs. There's no disassembly guide online either.

I did take the following measurements from the power supply board with all the cables connected and the blue power LED:

LED+ = 212.9V stable

+12V = 12.2V
+12V = 12.2V
BK/ON = 05.22V
ADJ = 04.33V
SGND = -002.6mV
SGND= -002.6mV

SGND = -003.4mV
SGND = -003.4mV
+5V = cable doesn't have any wire going to it
+5V = same as above
PS/ON = 04.11V
+5VSB = 05.25V
+5V = 05.23V
+5V = 05.23V
SGND = no wire connected
SGND = no wire connected
SGND = -006.3mV
+12V = 12.22V
+12V = 12.22V

+24V = 24.95V
+24V = 24.95V
SGND = -006.0mV
SGND = -006.0mV

The only reason I'm still stumped is because of the lack of sound. I've read countless posts and seen videos of people fixing this issue, and it's always the LED strips, but they always mention they have sound.

[Manul]

Seems ok to me. This should be backlight LED failure (open) or a multi-failure. Assuming just backlight failure, the problem is that you don't know what state the TV is in. Is it supposed to automatically play hdmi stream, or does it need the source to be selected manually. It is possible, that ir requires manual selection and this is why you do not get sound. Or maybe someone played with a menu blindly and now it is in who-knows-what state.

I would look how a normal statup of this model looks, maybe on some youtube video? Does it show logo while starting, what place it is? Does it maybe go to black screen if there is wrong source selected? Repeat test with a strong flashlight on the places where you expect to see startup logo or something. It might be hard to see, try different angles of illiumination. Maybe it works afterall and you missed?

[ezenia]

So far it does this:

Bauhn logo shows up and stays there for about 5-6 seconds. After that, I can see a "no signal" message moving across the screen. If I press the menu button, it'll show the options.

I will be testing my laptop again shortly to see how it behaves when it is connected. Now that I know I can see something with a flashlight, I might be able to find out what's happening to the sound.