Samsung LA26C350D1 - No picture, no sound & RED LED indicator stays ON

[CougarGTR]

Hi!

I have a subject LCD TV that doesn't turn ON via the remote or touch switch. Upon supplying mains power (220VAC), the RED indicator LED stays ON (no blinks).

I open up the casing to find that there is no budging capacitors nor any visible component that looks burnt/out-of-shape. Thus, begin probing the board with a multi-meter. The Power Board's model no. is BN44-00368A. The schematic can be found at

Here are the set of steps I have taken so far to test the Power Board:
1) With the Main Board removed
- 13V is present at the CNM802 Pin 1 & 2 and Cathode of Diodes DM857 & DM857A
- 5.3V is present at the CNM802 Pin 9 & 11 and Cathode of Diodes DM851 & DM851A
- LCD backlight is ON

2) With the Main Board attached to the Power Board
- 13V is lost. CNM802 Pin 1 & 2 drops to 0.9V. Cathode of DM857 & DM857A increased to 23V and fluctuates wildly
- 5.3V remains present at CNM802 Pin 9 & 11 and Cathode of DM851 & DM851A
- Backlight is OFF
- NO voltage detected at BLU_ON, 5.3V_DET & PS_ON

3) After leaving the Power ON to the unit for around 15mins
- TV turns ON by itself

4) After leaving the unit ON for another 10mins
- Unit switches OFF itself automatically
- 13V is lost again. CNM802 Pin 1 & 2 drops to 0.9V. Cathode of DM857 & DM857A increased to 23V and fluctuates wildly
- 5.3V remains stable.
- NO voltage detected at BLU_ON, 5.3V_DET & PS_ON

5) Suspecting that CM805 might be causing the problem, I removed the glue (originally glued to the transformer) and push it away from the transform, allowing it to stand independently and plug the mains out for about 3hrs to reset everything.

Plug the Mains back and power on, the TV is fully functional again and allowed me to use it for another 6 more hours with deliberate switching the unit ON and OFF several times via the remote. After around 6 hours, the unit called it quit and went back to the initial state i.e., Red LED stayed ON and no doesn't power up (as in (4)).

As I am a novice, I need to seek help from you guys. Hope to learn from all the experts here on where to start looking and to solve the problem?

Thanks in advance!

[vinceroger69]

Re: Samsung LA26C350D1 - No picture, no sound & RED LED indicator stays ON

when the set does not power up if you heat the power supply up with a hair dryer for a few minutes etc does the tv start up?

[CougarGTR]

Re: Samsung LA26C350D1 - No picture, no sound & RED LED indicator stays ON

Thanks for replying!

I tried the hair dryer test on the Power Board and it has no effect. The TV remains OFF with a solid Red LED ON.

[vinceroger69]

Re: Samsung LA26C350D1 - No picture, no sound & RED LED indicator stays ON

Maybe try the heat test on the mainboard too as not sure if bad bga soldering will cause this issue?

[CougarGTR]

Re: Samsung LA26C350D1 - No picture, no sound & RED LED indicator stays ON

Hi! Tried warming the Main Board with the hair dryer test too... No effect.

[dskall]

Re: Samsung LA26C350D1 - No picture, no sound & RED LED indicator stays ON

If you could post voltages in this format. I have trouble when they are scattered.

Need voltages from connector that goes from power supply board to main board. Will need pin#- PIN DESCRIPTION -Pin voltage in standby-Pin voltage when pushing power button and picture of connector on power supply board.
Format:
Pin# - Pin Description - Pin Voltage standby - Pin voltage power on
1 - XXXXXXX - XXv - XXXv
2 - XXXXXXX - XXXv - XXXv
3 - XXXXXXX - XXXv - XXXv
4 - etc.

[CougarGTR]

Re: Samsung LA26C350D1 - No picture, no sound & RED LED indicator stays ON

Thank you for the reply!

I have conducted the voltage reading from the connector (between the Power Board and Main Board).

I don't think the unit is able to enter Power_ON_Sate given that there is no response from the unit upon pressing the ON button on both the remote control (and physical touch-button). Also, there seems to be no difference in the Voltage readings when toggling the ON button on both the remote or panel touch-switch as well. I could using the wrong measuring equipment to do this test (i.e., DMM).

The voltage readings are as follows:
Pin# - Pin Description - Pin Voltage standby - Pin voltage power on
===================================================================
1 - A13V - 0.487V - 0.487V
2 - 5.3V_DET - 0V - 0V
3 - A13V - 0.486V - 0.486V
4 - BLU_ON - 0.064V - 0.064V
5 - GND - 0V - 0V
6 - E_PWM - 0.05V - 0.05V
7 - GND - 0V - 0V
8 - GND - 0V - 0V
9 - A5.3V - 5.29V - 5.29V
10 - GND - 0V - 0V
11 - A5.3V - 5.3V - 5.3V
12 - PS_ON - 0V - 0V

I went on to conduct the test again with the Main board disconnected from the Power Board (by removing the connector). The readings are as follows:
Pin# - Pin Description - Pin Voltage
====================================
1 - A13V - 12.97V
2 - 5.3V_DET - 2.39V
3 - A13V - 12.97V
4 - BLU_ON - 5.26V
5 - GND - 0V
6 - E_PWM - 5.19V
7 - GND - 0V - 0V
8 - GND - 0V - 0V
9 - A5.3V - 5.3V
10 - GND - 0V
11 - A5.3V - 5.3V - 5.3V
12 - PS_ON - 1.09V

[dskall]

Re: Samsung LA26C350D1 - No picture, no sound & RED LED indicator stays ON

Seems your power board is good. I would check your buttons and cable for voltage and a voltage change when pushing buttons. Check the voltage regulators on your mainboard.

[CougarGTR]

Re: Samsung LA26C350D1 - No picture, no sound & RED LED indicator stays ON

Thanks for the pointer! I shall start looking into that.