Changhong 50" LED tv, model LED50YC2000UA

[jackal68]

Hi

I picked up this 50" LED tv (Changhong model LED50YC2000UA) that suffered a power surge and it no longer turns on. The red standby light is on when plugged into the wall, but nothing happens when the power is pressed.

I opened it up and physically, the power supply board looks good, no burnt marks or bulging caps. I tested the voltage reading from the PS and got the 12V going into the MB, but did not get the 24V going into the LED board. I am wondering if this is a sign that the PS is bad or that the 24V will only go on when the MB is working properly and sends a signal for it to turn on.

I am attaching pictures of the tv, hopefully someone can direct me to the problem.

Thanks

[Dgtech]

Re: Changhong 50" LED tv, model LED50YC2000UA

The second part is usually the case. The power isnt fully on until it is told to do so. The main board usually is what tells the power supply to turn on. What is the voltage on PS_on pin of the power board? Actually, post all of the voltages that you get so far on that connector.

[jackal68]

Re: Changhong 50" LED tv, model LED50YC2000UA

The second part is usually the case. The power isnt fully on until it is told to do so. The main board usually is what tells the power supply to turn on. What is the voltage on PS_on pin of the power board? Actually, post all of the voltages that you get so far on that connector.

On the cable that goes to the mainboard, i only get the 12v (three of them). All the rest are 0v

On the cable that goes to the led driver board, I only get the 12.3v (one of them). All the rest are 0v.

so, to answer your question, PS_on is 0v

[Dgtech]

Re: Changhong 50" LED tv, model LED50YC2000UA

Ok, that PS_on should be 3.5 -- generated by the power supply. Check for a shorted diode or other defective parts.

[jackal68]

Re: Changhong 50" LED tv, model LED50YC2000UA

Ok, that PS_on should be 3.5 -- generated by the power supply. Check for a shorted diode or other defective parts.

Should it be 3.5v on both cables, the one going to MB as well as the cable going to the LED driver (as both cables have a PS_on).

[Dgtech]

Re: Changhong 50" LED tv, model LED50YC2000UA

I'm currently watching a video on youtube about this set. Here is the link.
https://www.youtube.com/watch?v=VwLf7ZGugUo

[Dgtech]

Re: Changhong 50" LED tv, model LED50YC2000UA

Once we get the 3.5 on the one coming from the power supply then we will see if the other one has it. It should be the same 3.5, but i dont know without seeing a schematic.

[Dgtech]

Re: Changhong 50" LED tv, model LED50YC2000UA

On this video, this guy has similar symptoms and his problem ends up being a 3.3v regulator not regulating on the main board which overheats the processor. It may not be the same thing but its a good video to get you familiar with some of the set.

[jackal68]

Re: Changhong 50" LED tv, model LED50YC2000UA

Thanks...it was a very helpful video! Im going to troubleshoot the PS and while I'm at it, i might check the voltage on that regulator in the MB.

[jackal68]

Re: Changhong 50" LED tv, model LED50YC2000UA

I started with the same diode on the video....just wondering if my readings are within specs in reference to his. When he measured the first diode, he got .39 drop....i get .34.

When he measures the BR, he gets .57, .55. .57 and .565 (all around .57).....i get .50, .48, .49 and .48. I'm wondering if these are off or are they just depending on the meter that you are using?

As expected, there is no 3.3v on the regulator on the MB.....

[budm]

Re: Changhong 50" LED tv, model LED50YC2000UA

BTW, PS-ON is NOT generated by the power supply, that PS-ON command signal comes from the main board and it will be present when TV is turned ON.
The PS-ON is used for turning on the rest of the switched power supplies.

[jackal68]

BTW, PS-ON is NOT generated by the power supply, that PS-ON command signal comes from the main board and it will be present when TV is turned ON.
The PS-ON is used for turning on the rest of the switched power supplies.

Does that mean I should be looking on the mainboard and not the PS? I'm not sure what I would be checking.

[budm]

Re: Changhong 50" LED tv, model LED50YC2000UA

Does that mean I should be looking on the mainboard and not the PS? I'm not sure what I would be checking.

Yep, all you can do (without the main board diagram) is to do good visual inspection, look to see if the HDMI IC is daamged or not, see if there is any fuse on the main board, check the input/output/adj pins Voltage of the Regulator, etc.

[jackal68]

Re: Changhong 50" LED tv, model LED50YC2000UA

Yep, all you can do (without the main board diagram) is to do good visual inspection, look to see if the HDMI IC is daamged or not, see if there is any fuse on the main board, check the input/output/adj pins Voltage of the Regulator, etc.

I looked at the mainboard and it looks like the regulator that was talked about in the video is burnt.

https://goo.gl/photos/DmYqsYHtk9zS6J347


Can someone confirm that it is burnt and it has a tiny hole?

[budm]

Re: Changhong 50" LED tv, model LED50YC2000UA

Is that the picture of YOUR 3.3V fixed Voltage regulator IC? You can easily verify by checking the Voltages.

[jackal68]

Re: Changhong 50" LED tv, model LED50YC2000UA

Is that the picture of YOUR 3.3V fixed Voltage regulator IC? You can easily verify by checking the Voltages.

Yes, I believe it is. In one of my earlier posts, I stated I had 0v (neg on ground and red on the middle pin).

[budm]

Re: Changhong 50" LED tv, model LED50YC2000UA

But you do have input Voltage of 5V to the input of the regulator, right?
And the resistance between the GND and the output pin is >500 Ohms?

[jackal68]

Re: Changhong 50" LED tv, model LED50YC2000UA

But you do have input Voltage of 5V to the input of the regulator, right?
And the resistance between the GND and the output pin is >500 Ohms?

Yes, the input voltage is at 5v, but there is no resistance between any of the pins...they all seem shorted.

[budm]

Re: Changhong 50" LED tv, model LED50YC2000UA

Yes, the input voltage is at 5v, but there is no resistance between any of the pins...they all seem shorted.

It cannot be all shorted! How can you have 5VDC to the input pin if it is shorted?
What Ohms scale are you using? What is the ACTUAL readout on the meter display?

[jackal68]

Re: Changhong 50" LED tv, model LED50YC2000UA

It cannot be all shorted! How can you have 5VDC to the input pin if it is shorted?
What Ohms scale are you using? What is the ACTUAL readout on the meter display?

You're right...wrong scale. When I put in the 200 ohms scale, i get the following:

GRD and In - 53.8 ohm
GRD and Out - 1 ohm
In and Out - 54.4 ohm