Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

[habznation]

I have a Sanyo FVD48P4 with good audio and an LED backlight that just flashes once.


*** LED driver voltage with and without load starts at ~60v and decays to 0.***

I checked each indiviudal LED with 3.3v and found 5 open or shorted LED's.

I got 3 replacement zener diodes from a TV repairshop, and replaced 3 bad LED's. I replaced the other two bad LED's with 5mm 35000mcd LED's I had from eBay as a trial, because i had no other zeners.



The TV shop checked all capacitors and verified good capacitance.

Same issue

I have looked everywhere on the All-in-one motherboard for any type of LED inverter fuse of any type and cannot see one......I have looked hard online for a service manual for this board, with no luck.....

Any help anyone could provide be greatly appreciated......

Thank You!!

[habznation]

Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

.

[Andrew F. Ali]

Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

So you found both bad LEDs and Zener diodes or did you replace bad LEDs with zener diodes??

[habznation]

Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

[QUOTE=Andrew F. Ali;732556]So you found both bad LEDs and Zener diodes or did you replace bad LEDs with zener diodes??[/QUOTE

thank you for the reply!

i replaced 3 bad LED's with zeners yes........the other 2 bad ones i tried replacing with actual LED's i had from something else

[budm]

Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

What is the current rating of the 5mm sub LEDs?
Did you put the Zener diodes in the reverse bias position?
3.3V 1W Zener?

[habznation]

Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

What is the current rating of the 5mm sub LEDs?
Did you put the Zener diodes in the reverse bias position?
3.3V 1W Zener?

no i didnt put them reverse bias! thank you! i put the stripe to the negative where the LED would go! So reverse them?

as for the substitute LED's , i checked on ebay where i got them and apparently theyre 20mA

[budm]

Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

Ar 20mA rating it will burnt so fast, the LEDs in the TV are rated at 1W with about 300~400mA rating.
If you put ZENER in forward bias mode the Vf will be only 0.6~0.7V range.

[habznation]

Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

Ar 20mA rating it will burnt so fast, the LEDs in the TV are rated at 1W with about 300~400mA rating.
If you put ZENER in forward bias mode the Vf will be only 0.6~0.7V range.

thank you very much budm, i will reverse them

further, i will get more zeners tomorrow and use them instead of these LED's

BUT, should my voltage be decaying like that? shouldnt it be holding? I'm measuring with the LED's connected and again with them disconnected and its the same.....starts at around 60v and slowly drops to 0

[budm]

Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

It sounds like it detected fault so it goes into shutdown mode.