sanyo dp46142 backlight issue.

[Herbssat]

Re: sanyo dp46142 backlight issue.

Not to hijack this thread but I have the same power correction issue with the sanyo that i am working on tech 2014. Is this something that is pulled down by the mainboard? How did you approach repairing the problem? All i have is the typical 165 or 170vdc with the power on or off. The power board is identical.

[hicksvilleshick]

Re: sanyo dp46142 backlight issue.

did you check the PFC voltage?

Just did that now, assuming we did it correctly, it read out like that, much the same with power on...

kinda fluctuated a bit. but .056 was the highest it got. unless we set the meter wrong or are supposed to ground to the other side of the cap?

[Alastair E]

Re: sanyo dp46142 backlight issue.

Not Quite.....

You need to measure the voltage Across the Cap, not from the cap to chassis.

Take-care, There should be up to 400V on that cap, so don't slip with the test-probes!.....

[hicksvilleshick]

Re: sanyo dp46142 backlight issue.

Not Quite.....

You need to measure the voltage Across the Cap, not from the cap to chassis.

Take-care, There should be up to 400V on that cap, so don't slip with the test-probes!.....

ahhh thank you... I couldn't get a definitive answer as to what I should probe...

171 plugged in but off.
169 plugged in and on.

:chug:

[budm]

Re: sanyo dp46142 backlight issue.

That is correct reading, there is no PFC Voltage booster in this power supply board so what you are getting is correct.
What DC Voltage do you get on that yellow cap on the LED driver board when the backlights go out? I have a feeling that the LED goes open circuit in the LED string.

[hicksvilleshick]

Re: sanyo dp46142 backlight issue.

That is correct reading, there is no PFC Voltage booster in this power supply board so what you are getting is correct.
What DC Voltage do you get on that yellow cap on the LED driver board when the backlights go out? I have a feeling that the LED goes open circuit in the LED string.

0v on or off

your talking about the yellow one on this board right?

by the way backlights still just flicker at startup. light on front stays green (didn't know if this factored in)

we tried to split it open enough to find the backlights and we got it apart but can't ID everything and didn't know how much to baby the parts being we were into the screen area.

[budm]

Re: sanyo dp46142 backlight issue.

"your talking about the yellow one on this board right?" Yes.
"0v on or off" That can't be right, you measure it right at the two legs?
There is a fuse that is connected to the + leg of the cap, it must have voltage there otherwise you will not have backlights at all.

[hicksvilleshick]

Re: sanyo dp46142 backlight issue.

"your talking about the yellow one on this board right?" Yes.
"0v on or off" That can't be right, you measure it right at the two legs?
There is a fuse that is connected to the + leg of the cap, it must have voltage there otherwise you will not have backlights at all.

yes measured at the legs.

no backlights at all meaning no flicker at startup even?

I wonder if I put the multimeter on the wrong setting?

lemme go back out there and see with the automatic one.

auto wouldn't sit still, re did with big meter and got 24v I apparently brought the fail the first time.

[hicksvilleshick]

Re: sanyo dp46142 backlight issue.

Any suggestions?


:chug:

[hicksvilleshick]

Re: sanyo dp46142 backlight issue.

:\

[Herbssat]

Re: sanyo dp46142 backlight issue.

Hey there Hicksville. You are fortunate to at least have a driver board you can get to. The Sanyo that i have on the bench has everything embedded into the samsung panel. This is going to be a real pain to fix. One of the other posters gave you some good ideas. Something is cutting out and you will have to monitor the voltages to find out and eliminate the culprit. I would probably say bad leds or power supply if i were a betting man.

[hicksvilleshick]

Re: sanyo dp46142 backlight issue.

Hey there Hicksville. You are fortunate to at least have a driver board you can get to. The Sanyo that i have on the bench has everything embedded into the samsung panel. This is going to be a real pain to fix. One of the other posters gave you some good ideas. Something is cutting out and you will have to monitor the voltages to find out and eliminate the culprit. I would probably say bad leds or power supply if i were a betting man.

Yeah that sounds like sense.

Can anyone point me to how to get to and troubleshoot the leds? I'd pull the trigger on a new powersupply if I could rule out the leds...


:chug:

[Herbssat]

Re: sanyo dp46142 backlight issue.

Hey Hicksville. Did you open the panel completely? I opened the samsung panel that I have all the way to the backlight led driver board. What an aggravating job. Driver board not putting out enough voltage to drive the LEDs. I have 43 in this panel.

[hicksvilleshick]

Re: sanyo dp46142 backlight issue.

Hey Hicksville. Did you open the panel completely? I opened the samsung panel that I have all the way to the backlight led driver board. What an aggravating job. Driver board not putting out enough voltage to drive the LEDs. I have 43 in this panel.

we tore it all the way down to where we got shaky enough to stop as we didn't want to separate something that wasn't supposed to be.... when we got to where we could pull the clear panel away I panicked and we put it back. lol


:chug:

[hicksvilleshick]

Re: sanyo dp46142 backlight issue.

anyone got any links to dissassembly to get to the panel? troubleshooting a bad led?

[hicksvilleshick]

Re: sanyo dp46142 backlight issue.

Said screw it and tore it down to where I followed the wires from the driver board were going... Promptly stripped out one of the phillips heads holding the metal and had to drill that out... was fun. Here's what I found.






So I ask, can that one be bypassed? I'm guessing it's bad/damaged, I can't definitively say if a screwdriver got to it or not, but I don't recall having to pry on anything this deep into the tv. Whats the fix here?

[budm]

Re: sanyo dp46142 backlight issue.

You can put two AA in series to get 3V, then put 100 Ohms 1/4W or more in series with the positive then you use that setup to test each LED, the LED has one round corner so that should be the Cathode side which the Negative of the battery will be connected, the other end will be Anode which will be connected to the end of the resistor.

[hicksvilleshick]

Re: sanyo dp46142 backlight issue.

Ok thanks bud, I'll see if I can come up with a resistor to try that with. I'm also being told I can just jump it and see if the backlight comes on and stays on... I'm drawing a blank as to what I may have that I can use to jump that...


:chug:

[budm]

Re: sanyo dp46142 backlight issue.

If the drive circuit is a true constant current source then you can jump it, it if is not then you may or may not damage the good LEDs.
You can use 6 Silicon diodes (such as 1n4007) connected in series to simulate 3.6V Voltage drops of the White LED. The Diodes will get quite hot so do not do it too long.

[hicksvilleshick]

Re: sanyo dp46142 backlight issue.

well took out the bad led, cleaned the paths, put it back together and same result, backlight flashes at startup but won't stay on.

So now I guess I need to jump the pins where the led was right? it had 4 legs off it, so what do I jump? I have traced the paths and this led board has 1 + and 4-, the 4 - go to 4 different sections of the led board.

So I guess I'm wondering if I just solder the + to the - or what? do I have to mess with the pads where the other 2 legs off the led were going? do I jump them too or leave them open?

:chug: