Bush 32" LED backlight problem.

[diif]

Hello, got a Bush 32" smart tv here. I think it's a Vestel.
Powers on ok, i can shine a torch and see a picture and i have sound.
The LED backlights don't always come on.
Any pointers where to start looking ?
Thanks

[diif]

Re: Bush 32" LED backlight problem.

I've taken some readings. I don't know if they are helpful.
Connector 4 at the top of the board

24v=24.51v

Connector 2 on the right hand side

12v=12.66v
5v=5.07v
PS/ON=4.4v

[diif]

Re: Bush 32" LED backlight problem.

Here's the back of the board.

[ERICSSON89]

Re: Bush 32" LED backlight problem.

there may be a bad component in the board like shorted transistors, cap, or maybe one of the transformer that's is used to supply high voltage to ccfl lamp.
All u have to do is resistance check them.

[ReeceyBurger123]

Re: Bush 32" LED backlight problem.

there may be a bad component in the board like shorted transistors, cap, or maybe one of the transformer that's is used to supply high voltage to ccfl lamp.
All u have to do is resistance check them.

Seen as the rest of the set powers on fine it sounds like the inverter section on the psu is going bad, looks like the psu has the inverter built on to it take the psu out and get 1000ohm + resistor bridge it to the pson to ground and see if the psu gives the voltages straight away, test it around 10 times.

[ReeceyBurger123]

Re: Bush 32" LED backlight problem.

there may be a bad component in the board like shorted transistors, cap, or maybe one of the transformer that's is used to supply high voltage to ccfl lamp.
All u have to do is resistance check them.

That doesn't help, there are no ccfl lamps in this set it is an led set.

[diif]

Re: Bush 32" LED backlight problem.

Thanks, Reecey, is that with the ribbon cable detached or plugged in ? Is the resistor to simulate a load ? can it be much bigger than 1000ohm like 10kohms ?
Thanks

[ERICSSON89]

Re: Bush 32" LED backlight problem.

oh I should have seen it well. sorry for the omission guys.

[ReeceyBurger123]

Re: Bush 32" LED backlight problem.

Thanks, Reecey, is that with the ribbon cable detached or plugged in ? Is the resistor to simulate a load ? can it be much bigger than 1000ohm like 10kohms ?
Thanks

Your welcome, the resistor is to simulate a load to get the psu to start so you can see if the volatges come up, I think 10k ohm will do it, if the volatges dont come up first time you can put it down to the psu.

[ReeceyBurger123]

Re: Bush 32" LED backlight problem.

oh I should have seen it well. sorry for the omission guys.

No worries, thanks for the input anyway

[ReeceyBurger123]

Re: Bush 32" LED backlight problem.

Just a quick question where does the wire coming off the psu go, does it go straight to the back light or to an inverter I cant tell from the photo, if it goes to the backlight be very careful as it will have a very high voltage.

[budm]

Re: Bush 32" LED backlight problem.

Where does the cable go to in the picture?
There should be LED DRIVER circuit/board some where that being fed with 24VDC from the power supply.
"PS/ON=4.4v" The PS_ON is present otherwise you will not be getting the 24V. You need to find out if the 24VDC or the BL_ON goes away when the backlights go off. Did you look at the power supply board real close to see if it has any bad solder joints?
BTW, what is the model number of this TV?

[diif]

Re: Bush 32" LED backlight problem.

Thanks guys, i can't believe i missed it, the wires disappear behind some black tape in the middle of the screen.
Here are the measurements from the two connectors.

0v, 30.2v | 30.3v, 44.7v power on but back light not powering on.

207mv, 19.8v | 19.8v, 38.5v power on, back light working.

I've been over the board and resoldered all of the joints. First thing this morning the back lights were not working, but they came on after about 10 minutes. The TV seems to be behaving now it's warm. Turning off then on and the back lights are working.
I am going to turn it off and leave it to get cold and come back to this later today.
The top heatsink is getting quite warm, i will pull off the cap to the left and measure it first.

[ReeceyBurger123]

Re: Bush 32" LED backlight problem.

Thanks guys, i can't believe i missed it, the wires disappear behind some black tape in the middle of the screen.
Here are the measurements from the two connectors.

0v, 30.2v | 30.3v, 44.7v power on but back light not powering on.

207mv, 19.8v | 19.8v, 38.5v power on, back light working.

I've been over the board and resoldered all of the joints. First thing this morning the back lights were not working, but they came on after about 10 minutes. The TV seems to be behaving now it's warm. Turning off then on and the back lights are working.
I am going to turn it off and leave it to get cold and come back to this later today.
The top heatsink is getting quite warm, i will pull off the cap to the left and measure it first.

When it fails to start the backlight, use a hair dryer and heat the psu and other boards to see if being warm definalty helps, then only heat sections of the board to try and help find whats going bad.