Samsung lcd tv no power

[taft1957]

Samsung LCD TV UN60EH6003F power it on and you just get the standby light, no back light, no data with flashlight test. However, when you disconnect the cable from power supply to the main board. The back light comes on immediately. This tells me it's a main board problem. The main board is BN94-06143A
I know most would just replace it, but I love to repair one. I don't know much about SMD components. Is this a transistor? I have attached a picture. It fails a diode test, and it looks burned. In the picture the leads look burned, but I don't see that looking with my eyes. Need to be educated on this part. Any common component failures on this board? Please help. If this is the bad part, I can't read the number. Sure could use a part number.

Thanks
Taft

[budm]

Re: Samsung lcd tv no power

Is this your board?
http://www.shopjimmy.com/samsung-bn9...eh6003fxza.htm
It looks like Voltage regulator IC.
Which one in your pictures, IC601 or 602? P/N as printed on the body? You may be able to clean up the body with Alcohol.
Can you zoom out?

[taft1957]

Re: Samsung lcd tv no power

Is this your board?
http://www.shopjimmy.com/samsung-bn9...eh6003fxza.htm
It looks like Voltage regulator IC.
Which one in your pictures, IC601 or 602? P/N as printed on the body? You may be able to clean up the body with Alcohol.
Can you zoom out?

Yes that is my board. I have tried to clean it off but it seems like heat damage, and it will not clean off. It is very close to the white connector going to the power supply. I can't read anything on the chip, and i don't see a location number for the chip. I have zoomed out a bit here is the attachment. Shows the white connector and the regulator.

[budm]

Re: Samsung lcd tv no power

The picture in SJ shows IC601 right above the metal tab of that device, that print should be on the same location as your board if your board is the same as the one shown at SJ.

[budm]

Re: Samsung lcd tv no power

What Voltages do you on each pin with ref to the chassis GND when power switch is activated (do not worry about if the TV comes on or not)?
Notes: the cut middle leg is electrically connected to the metal tab.

[budm]

Re: Samsung lcd tv no power

BTW, what happen if you disconnect the cable to the T-CON board?

[R_J]

Re: Samsung lcd tv no power

I wonder if that is just cooked glue on the component from the label that is usually in that location

[budm]

Re: Samsung lcd tv no power

OK, that part is under the sticker!
Acetone should be able to remove the glue.

[taft1957]

Re: Samsung lcd tv no power

BTW, what happen if you disconnect the cable to the T-CON board?

nothing I can disconnect all the cables to the main board, and with the cable connected between the power supply and the main board, still no back light. Unplug it and the back light will come on. That confirms the problem is on the main board. I just can't locate the short.

[ngth82]

Re: Samsung lcd tv no power

Can you post a clear picture of your main board with the sticker removed? I'd like to see this in its entirely.
Instead of using a diode test, measure the impedance (in ohms). The component that you took pictures of looks to be a LDO (linear voltage regulator) in a DPAK based on the layout.


Lets try a few things:

Measure voltage
- Turn the TV on
Put the GND lead on the chassis ground. Use the positive lead and measure the following locations:
- Voltage Bottom pin
- Voltage top pin (closer to the DRAM)?
- Voltage tab tab (right hand side)

Impedance measurements:
- Turn the tv OFF
What impedance (ohm) measurement values do you get if you measure the following combinations:
- Bottom pin (closer to white connector) to the top pin (closer to the DRAM)?
- Bottom pin to the tab (right hand side)
- Top pin to the tab

Do you have a soldering iron that can remove the part? If so, please remove it and measure the impedance again and report out. If the plastic casing really looks melted/burned, then i would assume there is also damage to the LDO inside. The next step is to figure out WHY it burned up... and where a short may be located.

[taft1957]

Re: Samsung lcd tv no power

What Voltages do you on each pin with ref to the chassis GND when power switch is activated (do not worry about if the TV comes on or not)?
Notes: the cut middle leg is electrically connected to the metal tab.

With that cable plugged in coming from the power supply. The 12 V line is pulled down to 0.25 milivolts, and the five volt line is also pulled down to 0.25 milivolts. I removed the suspected voltage regulator from the main board, and all voltages still bottom out. If I remove the bad part from the main board, that would lift the short and my back light would come back on. Right?

[budm]

Re: Samsung lcd tv no power

With that cable plugged in coming from the power supply. The 12 V line is pulled down to 0.25 milivolts, and the five volt line is also pulled down to 0.25 milivolts. I removed the suspected voltage regulator from the main board, and all voltages still bottom out. If I remove the bad part from the main board, that would lift the short and my back light would come back on. Right?

With that cable plugged in coming from the power supply. The 12 V line is pulled down to 0.25 milivolts, and the five volt line is also pulled down to 0.25 milivolts. I removed the suspected voltage regulator from the main board, and all voltages still bottom out. If I remove the bad part from the main board, that would lift the short and my back light would come back on. Right?

Well, is that part shorted out? Did you check the Voltages on or 3 pins of that device as requested?
How did you know if that device is shorted or not? Did you check the resistance of all 3 pins with ref. to GND? There are steps that you need to follow.
Pin one of that device looks to be connected to GND, the other 2 pins look to be for input and output.
The switched 12V and the switched 5V will not come on until it gets the PS-ON from the main board, so they are not pulled down they are getting the command signal to come on.
You need to read basic TV troubleshooting first to know what the command signals are and what they are for.
You are trying to troubleshoot down to component level on a complex main board so I would not start removing parts without knowing what the parts are.

[taft1957]

Re: Samsung lcd tv no power

OK, that part is under the sticker!
Acetone should be able to remove the glue.

I used acetone, alcohol, goop off. I don't think it was glue. When i removed that transistor, it just crumbled apart.

[taft1957]

Re: Samsung lcd tv no power

OK, that part is under the sticker!
Acetone should be able to remove the glue.

I used acetone, alcohol, goop off. I don't think it was glue. When i removed that transistor, it just crumbled apart. So there is no question, that part got very hot.

[taft1957]

Re: Samsung lcd tv no power

Well, is that part shorted out? Did you check the Voltages on or 3 pins of that device as requested?
How did you know if that device is shorted or not? Did you check the resistance of all 3 pins with ref. to GND? There are steps that you need to follow.
Pin one of that device looks to be connected to GND, the other 2 pins look to be for input and output.
The switched 12V and the switched 5V will not come on until it gets the PS-ON from the main board, so they are not pulled down they are getting the command signal to come on.
You need to read basic TV troubleshooting first to know what the command signals are and what they are for.
You are trying to troubleshoot down to component level on a complex main board so I would not start removing parts without knowing what the parts are.

First question. How did I know the device was shorted? I thought is was a transistor, but I didn't know. You guys confirmed it was a regulator transistor. SO checked it several ways. First with diode test of my meter. Test bad. Then with ohm test, I read resistance both ways, and i got 0.54 and 0.56 I removed the part. It just crumbled as if it had got very hot. Not being able to read any of the numbers on it, also points to heat damage.
You stated the voltages are not being pulled down. This confuses me because when the cable is disconnected, and the back light is on. I have several voltages on the power supply. 12 volts and 5 volts. Then when the cable is attached to the main board, those voltages got o milivolts, every pin is nothing but milivolts or zero. So my question to you before. Doesn't that mean there is a short? How can they be getting a command signal to come on, if the main board is detached? When the cable is re-attached to the main board, following that 12 volt line to the main board, then I get only 0.25 milivolt reading. That is using black lead to chassis, and red lead to that 12 volt wire. You stated the 12 volts and the five volts don't come on until the power on command is given from the main board. How come I am reading them on the power supply with the main board detached?
I have repaired switch mode power supplies for over 30 years. It this smd technology and eeproms that i don't get. I do understand that the command signal turns on the eeprom,and that is suppose to turn on the tv. On power supplies I could find the shorted components from reading resistance to ground. Maybe my meter isn't good enough for these smd components. I am self taught. I have a lot to learn. I hate just replacing aboard. I get more satisfaction in repairing the board. I know this is a complex board, but it's still fun to try. Just wish it were as easy as lifting a shorted component off the board and having all my resistances returning to normal. Or voltages. I removed that part, because you guys told me what it was, SO i knew it was bad.

[budm]

Re: Samsung lcd tv no power

"Doesn't that mean there is a short? How can they be getting a command signal to come on, if the main board is detached?" The power supply has pull-up resistors for doing a self test when not connected to the main board, they did not do that in older TV so you have to provide the pull-up resistors which is not easy to do in the field service.

SMD and through hole device are not not different electrically, it is just difference form factor, SMD diode is the same as through hole diode, same for transistor, MOSFET, Transformer, capacitor.
so after you removing that Regulator, when you check the resistance between GND and each empty pad, what resistance do you get between each pad and GND?

" I read resistance both ways, and i got 0.54 and 0.56 I removed the part." Is that 0.54 and 0.56 Ohms and between which pin and which pin?

[taft1957]

Re: Samsung lcd tv no power

"Doesn't that mean there is a short? How can they be getting a command signal to come on, if the main board is detached?" The power supply has pull-up resistors for doing a self test when not connected to the main board, they did not do that in older TV so you have to provide the pull-up resistors which is not easy to do in the field service.

SMD and through hole device are not not different electrically, it is just difference form factor, SMD diode is the same as through hole diode, same for transistor, MOSFET, Transformer, capacitor.
so after you removing that Regulator, when you check the resistance between GND and each empty pad, what resistance do you get between each pad and GND?

" I read resistance both ways, and i got 0.54 and 0.56 I removed the part." Is that 0.54 and 0.56 Ohms and between which pin and which pin?

OK, Using the tuner for ground. I get 197.9 ohms on the bottom left pad. That is with my meter on ohms On the right pad I get 0.2 ohms. ON continuity check on the right pad I get a steady beep. On the top pad I get 0.522 k ohms So that is way different from when the part was on the board. That means there is a short somewhere on that trace. Right?

[taft1957]

Re: Samsung lcd tv no power

OK, Using the tuner for ground. I get 197.9 ohms on the bottom left pad. That is with my meter on ohms On the right pad I get 0.2 ohms. ON continuity check on the right pad I get a steady beep. On the top pad I get 0.522 k ohms So that is way different from when the part was on the board. That means there is a short somewhere on that trace. Right?

I took two more pictures. Just to the left of that transistor pad is a row of capacitors. At the very top of that row I have zoomed in one the top capacitor. From ground, and on the beep function of my meter I get a beep on both sides of that capacitor. In comparison to the others, which only beep on the negative side which is ground. SO is that capacitor shorted?

[budm]

Re: Samsung lcd tv no power

I would not using Beep function for testing for shorted circuit since the meter will beep with resistance as high as 50 Ohms or more depends on your meter, you can try checking with various resistor value to find out at what the resistance the meter will stop beeping.
Beeping function will tell you that you have electrical connection between point 'A' and point 'B'. Resistance result is the one you need to look for.
You should use low Ohm mode for looking for shorted circuit (something thing that has <1 or 2 Ohms reading). Ohm reading is the way to go for looking to see if you have shorted circuit/shorted parts or not.

[ngth82]

Re: Samsung lcd tv no power

I took two more pictures. Just to the left of that transistor pad is a row of capacitors. At the very top of that row I have zoomed in one the top capacitor. From ground, and on the beep function of my meter I get a beep on both sides of that capacitor. In comparison to the others, which only beep on the negative side which is ground. SO is that capacitor shorted?

It would help if you are able to mark up the photos in MSPaint or some other photo editor to clearly indicate which paragraph aligns with which pic.

In any case, the beep function isn't what you want to use. Budm mentioned the same thing. Use the low ohm measurement function of your meter to measure the resistance.

For the zoomed in picture (attached), the right hand side appears to be GND. Look at the copper pour (shape) on the board. By inspection, the majority of the 0402 and 0603 sized caps that you have here share the same net.

Since you say the the left hand side is also measuring low impedance to GND, it indicates the left hand net is shorted, but not necessarily across this cap.

What RESISTANCE value are you getting across this capacitor?