fixing possibly a bad power supplies board of a LED TV

MisterBill2

Joined Jan 23, 2018
6,343
Certainly measuring the voltage of the supply should show that either it is functioning or not. But please be very careful to not cause any short circuiting to other places while measuring. In other threads probing errors while measuring have caused additional failures.
Unfortunately, on most occasions, the component that is burned is not the part that caused the problem, but rather the unfortunate victim of an excess power surge caused by some other part failing. The result being that replacing only the burned part will only result in a second burned part. So additional analysis is required to learn the actual cause of the failure. Switching power supplies are a very challenging product to service, as a result.
 

Thread Starter

Leon_Chan

Joined Sep 11, 2019
81
Could someone talk about if this power board dangerous as it contains some 400V capacitors on it? And what cautions should be taken?

And does such power board of a LED TV no different from any other power supplies, which is only doing voltage stepping down and rectifying work.
 
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MisterBill2

Joined Jan 23, 2018
6,343
Could someone talk about if this power board dangerous as it contains some 400V capacitors on it? And what cautions should be taken?

And does such power board of a LED TV no different from any other power supplies, which is only doing power stepping down and rectifying work.
OK, YES!! The power supply module does contain both the mains voltage and the rectified mains voltage, which is a fairly high DC voltage.
ALSO, the area marked "HOT" is tied to the supply mains. Thus you need to not touch any parts of the board while it is powered. So there does exist a shock hazard while the board is energized.
Also, it means that the board must not be sitting on any sort of electrical conductor while you are checking it.
 

LesJones

Joined Jan 8, 2017
2,667
I would suggest checking the power supply with it connected to the rest of the TV as some supplies do not like having no load on them. Also be careful not to short adjacent pins on the connector as this could destroy a working power supply.

Les.
 

MisterBill2

Joined Jan 23, 2018
6,343
Check R12, R13 small resistors in the burned area next to the Yellow pulse Transformer ..
Those resistors do look sort of burned, BUT if they are they are certainly not the cause of the problem. Resistors in a properly designed circuit do not burn out for no reason. Some other component has failed. Either a diode has shorted or a transistor. Or possibly a capacitor has become leaky. A dual voltage power supply with those ratings should be an easily available thing to find. Not an exact replacement but a functional replacement. So mounting room may be an issue.
 

Thread Starter

Leon_Chan

Joined Sep 11, 2019
81
I get all components shown.
There are a board with IR and another with buttons, and also the main logic board that controls the hdmi , usb etc.
Could someone figure out what are the names of these components?
And suppose if the parts are provided separately for you, such as you buying it online, do you have simple way to test each component if it is working or not using some simple tools?
 

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LesJones

Joined Jan 8, 2017
2,667
You do not seem to be taking a logical approach to diagnosing the fault. You now seem to have thought of just changing board a random. You have been told how to check the output voltages from the power supply but you have not done this simple test. If your car would not start would you replace the engine before checking that there was fuel in the tank ?

Les.
 

MisterBill2

Joined Jan 23, 2018
6,343
If there was a reason to suspect tje power supply circuit board, and with that board being so very well marked, the best choice is to check it with a voltmeter. In fact there is no other reasonable choice.
Doing the checking without grabbing the wrong connection would not be difficult nor would it be unsafe, if you are able to focus your attention on that activity for the short time needed to do it. The ability to pay attention to what you are doing is a main requirement for safely working with active electrical systems.
 

Thread Starter

Leon_Chan

Joined Sep 11, 2019
81
Yes, the checking will be conducted *next week* as there need more space to do it.

In fact, I have a replacement of ayp25009 before. But substituted it, did not make the device working. A bad power board was my first guess. It may be possible other parts are faulty or I failed to assemble it back correctly. One of my past doubt if the pins arrangement are not the same on both ayp250009 and ayp250008 are now solved by checking the pins printout on the back of the two boards.

The work here is not a demonstration but the process of fixing a failed working LED TV. It would be good to get a little more understanding of what are inside the LED TV and how it works.
 

LesJones

Joined Jan 8, 2017
2,667
You have a great deal to learn to understand how a modern LCD TV works. You would first need to understand electronics and then the digital principles used to process the TV signals. Even when you understand that there will be components that you will not be able to obtain. It is not normally considered cost effective to do component level repaires.

Les.
 

MisterBill2

Joined Jan 23, 2018
6,343
You have a great deal to learn to understand how a modern LCD TV works. You would first need to understand electronics and then the digital principles used to process the TV signals. Even when you understand that there will be components that you will not be able to obtain. It is not normally considered cost effective to do component level repaires.

Les.
I find two reasons to not do component level repairs, the main one being that the components are not available or identifiable. The second reason being that the components are force fitted in plated through holes in a multilayer circuit board. And a third reason is no circuit information being available. Knowing the circuit and knowing how it functions, after being aware of the specific complaint, is usually enough to point in the direction of the failed part, or parts.

With tv sets the refusal of the makers to allow others to know the circuits is indeed a serious impediment. My solution would be to refuse allowing such equipment to be imported. That would certainly reduce the amount of poorly made electronics here in the USA. Not much chance of such a rule passing, but it certainly could be very effective.
 

Thread Starter

Leon_Chan

Joined Sep 11, 2019
81
After I check the voltage output of both boards ayp250009(new) and ayp250008(old), I find that both boards can output 12V. There are 4 wires connected to the main board which provides 12V x2 + Gnd x2. More details will be provided later and I can assume that the old board is working. As the new board only measure 9.3V in the main board, but the old board provide 12V measured, so I will use the old board.

The TV after connected again do not have anythings to see. The IR light is On. So what we can now to check what faults there will? We have these input, TV, HDMI like other TV.

The normal running of this LEDTV will load a logo screen and boot to the TV channels. Now there is nothing to see.
 

Thread Starter

Leon_Chan

Joined Sep 11, 2019
81
Why have you only tested the +12 volts output ? The TV will almost certainly also require the +5 volts.

Les.
Because the connector only have 4 wires connected to the main board. These are 12V +12V + Gnd + Gnd
Also, the 5V output of the old board are measured 0V, that is a bit strange.

The new board have both 12V and 5V outputs. But when measured at the main board, the 12V pin measured only have 9.3V in it.
 

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Thread Starter

Leon_Chan

Joined Sep 11, 2019
81
If the fault is not in the power board, that may mean I cannot get it fixed without replacing some other boards. Or we may go check any components if it is failed?
Should the led TV display "no signal" if no any input to it when normal?
The main board front and back images are shown here.
The pins marked 24V when measured is 0. Anyone know if this should be 24V and going to the panel?
What is 5VA mean in some pin?
 

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Thread Starter

Leon_Chan

Joined Sep 11, 2019
81
The panels and the connector is shown here. Make sure you see it in full.
Is there anyway we can do simple test to make sure it is not any of the LEDs fail?
Videos demonstrated how LEDs are replaced can be found in youtube.

I included many images in the zip file so anyone want to dig in can download from this link.
https://drive.google.com/open?id=1_S5dMvFNUg6Ea5K2WlGd9o5Lmk7pLYXF
 

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shortbus

Joined Sep 30, 2009
7,764
With tv sets the refusal of the makers to allow others to know the circuits is indeed a serious impediment.
After fixing a couple of them I have a take on why they don't give schematics out. They don't want people to know that many brands, both high and low priced ones use the same internal circuits now. So why would people buy brand "A" that is much higher priced over brand "B" that is the same internally and sells for half the price?
 

Thread Starter

Leon_Chan

Joined Sep 11, 2019
81
After fixing a couple of them I have a take on why they don't give schematics out. They don't want people to know that many brands, both high and low priced ones use the same internal circuits now. So why would people buy brand "A" that is much higher priced over brand "B" that is the same internally and sells for half the price?
Manufacturer will provide period of warranty and within which the product is repaired free of charge. There is no need for buyer to fix anything himself. People most often buy new and better one after it is failed and out of warranty. This makes providing the circuit diagram is not necessary.

Better product quality and service make a difference of the product price.
 

MisterBill2

Joined Jan 23, 2018
6,343
Because the connector only have 4 wires connected to the main board. These are 12V +12V + Gnd + Gnd
Also, the 5V output of the old board are measured 0V, that is a bit strange.

The new board have both 12V and 5V outputs. But when measured at the main board, the 12V pin measured only have 9.3V in it.
As I examine the connector on the main board there are only 4 pins, 2 for +12 and 2 for GND. Thus the +5 volts is not supplied to this board. Therefor no need to check it.
 
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