Sound and picture but no backlight

[JCdes]

Re: Sound and picture but no backlight

It has 5 led strips consisting of 14 leds each. I dont know the value of each led. The tester starts from 0v increasing the voltage to the strip and it lights up very dim at around 70v and stops increasing at 83v full brightness. Tried disconnecting the "adj" wire on the board and that did not work, just wanted to try and see if it made a diff.

[petehall347]

Re: Sound and picture but no backlight

are all led circuits same voltage on your tester ? must have connector unplugged from power board .
if they are plug it back in and see if magic happened . dont know what it is with my tester but 2 sets still running after doing just that .maybe i got lucky . been a couple of months at least now .
thinking about it though voltages from the supply and tester were not a lot different .

[JCdes]

Re: Sound and picture but no backlight

Yup all same voltage, same amount of leds on each strip. I did test unplugged from board.

[budm]

Re: Sound and picture but no backlight

You have 5 LED strings and each string has its own Cathode return line through MOSFET Q201, 205, 206, 207, and 208.
The red wires are the Anode wire for each string which are connected together and fed by one Boost converter.
All connectors in place, set the TV to OFF, keep black probe on the chassis, red probe on any one of the LED+, then turn on the TV while watching the meter (meter set to 200VDC) to see how high it goes up to then wait 10 seconds to see how low it goes to, turn the TV OFF, the repeat the same test using the red probe on all 5 LED - pins at a time.

[JCdes]

Re: Sound and picture but no backlight

59.8 on stdby 62.4v turned on. It does spike to 72 for a second then back to 62, power off is back to 59.8. Same behavior on all connections.

[JCdes]

Re: Sound and picture but no backlight

While I was at it, I saw 0v at the leg closest to the backlight header, gnd in center and .5v at the other leg on all q201,207,205,208 and 206. Both stdby and on. R255 had 67 on one side and climbs very slow to 12 on the other, R239 had 0v on both sides. I made a messy picture of a few measurements. D1a and D1b had -0v on anode and 5 on cathode side when powered on. D204 has 0v at all times.

[Diah]

Re: Sound and picture but no backlight

59.8 on stdby 62.4v turned on. It does spike to 72 for a second then back to 62, power off is back to 59.8. Same behavior on all connections.

i think yours measurements points not as the points other suggested.. you need the measurements on the LED SOCKETS

[JCdes]

Re: Sound and picture but no backlight

Those were taken at the led sockets, plugged and unplugged same results.

[Diah]

Re: Sound and picture but no backlight

Those were taken at the led sockets, plugged and unplugged same results.

if so are you sure you got 59.8V when set on STBY ????

[JCdes]

Re: Sound and picture but no backlight

Yes

[JCdes]

Re: Sound and picture but no backlight

Stdby 59.8 and 62.4 turned on. When I turn it on it spikes to 74 after 6 seconds or so then back down to 62. Turn off then back to 59, unplug and slowly goes down to 0...

[Diah]

Re: Sound and picture but no backlight

measure please the V on CON4 PL_ON pins when set on and STB

[dick_barton]

Re: Sound and picture but no backlight

Can you measure the voltage on the pins of U200. It may give some insight into what the problem could be.

[JCdes]

Re: Sound and picture but no backlight

I did measure that but cant remember if it was 4.9 I should have taken notes... I'll measure again when I get home. But it does go to 0 when turned off with power button.

[JCdes]

Re: Sound and picture but no backlight

Can you measure the voltage on the pins of U200. It may give some insight into what the problem could be.

Will do... I guess I'll have to juggle a bit since it is under the board. Can I measure just plugged in to the wall or do I need all connections to make it more accurate?

[dick_barton]

Re: Sound and picture but no backlight

I'm not sure what you mean by all connections.
Are you able to turn the board over and rest it safely on an insulated pad to make the measurements.

[JCdes]

Re: Sound and picture but no backlight

All connection I mean main board and led plugs... Yes I have insulation...

[JCdes]

Re: Sound and picture but no backlight

On my way back... I'll post measurements in about an hour..

[JCdes]

Re: Sound and picture but no backlight

11.2 on leg 1
4.6 on leg 8
1.7 on leg 7
6 on leg 6
2,3,4,5 0v
All cables connected

[JCdes]

Re: Sound and picture but no backlight

measure please the V on CON4 PL_ON pins when set on and STB

BL-On 4.8
Adjust 4.9