Samsung LN46B750 power issue

[dbruts]

There was a surge through the HDMI cable that fried the main assembly board resulting in a completely dead unit when plugged in. I ordered a replacement and installed. Now when powered, the standby light flashes quickly, but the screen does not turn on. When i unplug the power supply and the main board, the backlight turns on. I thought this might be a power issue so i also purchased power supply board. There are no bulging or cracked capacitors on either of the boards. After installing this, the standby light continues to flash very quickly. I have a voltmeter and feel comfortable testing. I do not have the ability to test the capacitors though. Any help would be greatly appreciated.

I have tested the pins on the cable from the power supply to the main board. Results are:
1 (POW ON/OFF) 4.37V
2 (H_Sync) 0-4.99 switching
3 (STB 5.3V)
4 (GND) 5.17
5 (GND) 5.17
6 (GND) 5.17
7 (13Vs) -7.59
8 (13Vs) -7.59
9 (GND) 5.15
10 (GND) 5.20
11 (GND) 5.20
12 (GND) 5.20
13 (5.3V) 0
14 (5.3V) 0
15 (5.3V) 0
16 (5.3V) 0
17 (GND) 5.19
18 (GND) 5.19
19 (13Vm) -7.58
20 (GND) 5.20
21 (13Vm) -7.58
22 (13Vm) -7.57
23 (INV ON/OFF) 0.06
24 (NC) -0.03
25 (E-PWM) -0.03
26 (GND) 5.17
27 (DET_SV) -0.03
28 (GND) 5.17
29 (GND) 5.15
30 (GND) 5.17

Other information:

• When everything connected and plugged in, there is no lights on the ethernet plug in.
• Red standby light flashes sold red for 4 seconds then 5 quick flashes and a one second red light then 12 quick flashes then repeat
• I have read resetting the EEPROM may help, but have not found any schematics to identify where the EEPROM chip is on the main board (BN94-02585C)
• When ordering an assembly board, I was sent an "alternate" part that is supposed to be interchangeable. when the part was plugged in, the tv powered on, but was unresponsive from remote control commands. I was able to see white noise, the sound worked, and i could change channels and volume. Input would not work and I was unable to reach any service menu (mute -> 1 -> 8 -> 2 -> Power)

[budm]

Re: Samsung LN46B750 power issue

"When i unplug the power supply and the main board, the backlight turns on." That is how you test to see if the power supply, backlights inveter circuits are good or not, in this case, it is good otherwise the backlights will not be on.
1 (POW ON/OFF) 4.37V Main board is sending the correct Power supply on signal.
23 (INV ON/OFF) 0.06. The main board is not sending out the backlights on signal, so this is bad.

"28 (GND) 5.17
29 (GND) 5.15
30 (GND) 5.17"
These cannot not be right. What do you use for ground ref. point?
Where did you get the main board from? Right now it is not sending out the correct signals.

[dbruts]

Re: Samsung LN46B750 power issue

"
23 (INV ON/OFF) 0.06. The main board is not sending out the backlights on signal, so this is bad.

To test, i unplugged the cord from the power supply to the main board and tested the cable at the main board end. when the cord is unplugged, it appears there should be no power going to the main board which then connects to the T-CON board, speakers, and remote control receiver. Does the 0.06 reading mean there is a signal being sent, but because the main board does not send anything back, the main board is bad?

"
"28 (GND) 5.17
29 (GND) 5.15
30 (GND) 5.17"
These cannot not be right. What do you use for ground ref. point?
Where did you get the main board from? Right now it is not sending out the correct signals.

I am unsure what you mean by ground ref. point. I am testing with pin 3 which is the (STB 5.3V) pin. I purchased the main board from HDTVPartstore. I was going to purchase from ShopJimmy (which everyone seems to recommend), but they were out of stock. Thank you again for your help and patience.

I have also added a couple updates to the main post

[dbruts]

Re: Samsung LN46B750 power issue

I am also using a Voltmeter set at 20 (DC line over three dots) for all tests.

[dbruts]

Re: Samsung LN46B750 power issue

Should I be testing with the cable plugged in from the power supply to the main board?

[budm]

Re: Samsung LN46B750 power issue

OK, let start with this test; disconnect the cable between the main board and the power supply board, if the backlights come on when you plug the power cord into the outlet, that means the power supply and inverter circuits are OK.
Can we also get the good pictures of the back side of the TV so we can see how all the boards are connected?
"When ordering an assembly board, I was sent an "alternate" part that is supposed to be interchangeable." This does not sound good.
BTW: What is the power supply board P/N. BN44-XXXXX?

[dbruts]

Re: Samsung LN46B750 power issue






If you need any other images let me know.

http://imgur.com/8AhJHhQ
http://imgur.com/mekoI5c
http://imgur.com/8AhJHhQ
http://imgur.com/qDtSXGg

[dbruts]

Re: Samsung LN46B750 power issue

When i remove the cable between the main board and the power supply, the backlight does turn on.

"When ordering an assembly board, I was sent an "alternate" part that is supposed to be interchangeable." This does not sound good.
BTW: What is the power supply board P/N. BN44-XXXXX?

I have a main board with part #BN94-02585C. I ordered from partstore and was shipped a replacement piece that they said was a "substitute" part.

[dbruts]

Re: Samsung LN46B750 power issue

Close up of main board. I also returned the main board that I received and purchased a board that matches.

[budm]

Re: Samsung LN46B750 power issue

OK, your power supply board and the inverter circuit are OK, so your new board is not working, but since the TV was hit with the surge we are not 100% sure if something else is good or not.
What is the P/N of the power supply board so we can verify all the output voltages of the power supply. T-CON board will also need to be checked.

[dbruts]

Re: Samsung LN46B750 power issue

P/N of power supply board is BN44-00266A

[dbruts]

Re: Samsung LN46B750 power issue

I will have to reposition the tv in order to get at the T-CON board.

[budm]

Re: Samsung LN46B750 power issue

So right now you have the correct main board installed?

[dbruts]

Re: Samsung LN46B750 power issue

Yes. It was the replacement with matching codes BN94-02585C

[dbruts]

Re: Samsung LN46B750 power issue

T-CON board images

[budm]

Re: Samsung LN46B750 power issue

OK, right now we know that we do have 5.3VSTBY, now we need to verify that the power supply does have 5.3V and 13V at CN801 connector, still leave the plug off the CN801 to the main board.

[dbruts]

Re: Samsung LN46B750 power issue

Sorry I am a little confused. When I took the readings, I tested like the layout in the image. Is the other image a close up of the CN801 to be tested?

[budm]

Re: Samsung LN46B750 power issue

OK, you can test with the connector still attached to the power supply board cn801, or without the connector in place but more chance of probe slipping.
The black probe of the meter will be connected to the metal chassis. then using the red probe to check each pin and report the readings.

[dbruts]

Re: Samsung LN46B750 power issue

Testing like image.

1 (POW ON/OFF) .8
2 (H_Sync) 0
3 (STB 5.3V) 5.21
4 (GND) 0
5 (GND) 0
6 (GND) 0
7 (13Vs) 12.78
8 (13Vs) 12.78
9 (GND) 0
10 (GND) 0
11 (GND) 0
12 (GND) 0
13 (5.3V) 5.21
14 (5.3V) 5.21
15 (5.3V) 5.21
16 (5.3V) 5.21
17 (GND) 0
18 (GND) 0
19 (13Vm) 12.78
20 (GND) 0
21 (13Vm) 12.78
22 (13Vm) 12.78
23 (INV ON/OFF) 5.12
24 (NC) 0
25 (E-PWM) 4.68
26 (GND) 0
27 (DET_SV) 5.16
28 (GND) 0
29 (GND) 0
30 (GND) 0

[budm]

Re: Samsung LN46B750 power issue

Good, the power supply is OK.
Put connectors back in place, but remove the cables between the T-CON and the main board to see if the TV will power up with different LED blinking code.