Sanyo DP26649 -00, No backlight, audio, image

[jaimegmr]

Hi everyone. I need your guidance in troubleshooting this TV. It is a Sanyo DP26649 with 00 chassis and N7GE main board. Service manual can be found here: http://www.tgohome.com/ServiceManual...6649&typekey=0

The green power LED does turn on and stays on until I push the power button again. The backlight never comes on. I have disconnected the 3 wire connector at K8L and the backlight does come on, but I see nothing on the screen (I pushed the buttons and no volume or channel indication appeared).
When TV is off:
5V_STBY = 5V
POWER_ON = 0V

When TV is ON (measured at K8B):
5V_STBY = 5V
POWER_ON = 5V
12V = 11.8V
5V = 5V
24V = 24V

I also measured P_FAIL and it was at 5V.
BL_ON was 0V and BL_ADJ was very low around 0.2V if I remember correctly.

Turned off the power and measured resistance across the collector and emitter of Q1751 and it was around 1.1k Ohm. I realize this is in the circuit so it may not mean much.

Any suggestions on what to do next?

[jaimegmr]

Re: Sanyo DP26649 -00, No backlight, audio, image

BL_ON voltage coming from Video Processor IC is 1.99V. It goes through R1767 into the base of Q1751. The voltage at the base is 0.66V. The voltage at the collector is 0V.

Next step is to remove Q1751? Or does the 1.99V mean the Video processor is bad?

[budm]

Re: Sanyo DP26649 -00, No backlight, audio, image

"The voltage at the base is 0.66V. The voltage at the collector is 0V. " That is what should be at the Collector, Q1751 is being bias on.
"I have disconnected the 3 wire connector at K8L and the backlight does come on" This will force on the backlights, but since there is fault on the main board, that is why you do not see any thing on the screen.
Disconnecting the K8L is how you find out if the problem is in the power supply-inverter board or in the main board. This model is know to have bad main board, I myself had to replace it.
http://s807.photobucket.com/user/bud...DP26649?page=1

[jaimegmr]

Re: Sanyo DP26649 -00, No backlight, audio, image

I removed Q1751. This resulted in the inverter being turned on. The voltage coming from the video processor is now 3.33V compared to 1.99V from before.

[budm]

Re: Sanyo DP26649 -00, No backlight, audio, image

The processor was stuck so it kept the transistor on, it should turn off the transistor to allow the Collector to rise up. You are getting 3.33V because it is not being loaded down by the Base resistor and the E-B junction of the transistor, that is normal.

[jaimegmr]

Re: Sanyo DP26649 -00, No backlight, audio, image

I've been looking for replacement mainboards and the only -00 boards I found are considerably more expensive than -05 mainboards. Seems like the only difference is that the -05 main board has an extra transistor and a few extra resistors not found in the -00 board.
Have you ever converted boards? I think the only thing I would need to do is remove the extra components and add 1 zero ohm jumper at one resistor location to make it match the -00 mainboards. The changes appear to be due to the use of different panel and LVDS cable.

[budm]

Re: Sanyo DP26649 -00, No backlight, audio, image

I bought my board from shopjimmy that matched my board. Not having the diagram for the board without knowing what the extra components are for is taking a chance.