Crappy Vestel/Sharp LC-40FG3141K Set Backlight going off randomly

[90Ninety]

Hello
Model Code Sharp LC-40FG3141K

Firstly perhaps I should save myself the agony and throw this set out ? Then again I hate E-waste , or giving a person further headace in the far east or Agbogbloshie . So I digress to my last hope of fixing this pile of shite , with the dash of hope from your combined experiences

So this set is randomly turning off its backlight ( could be days, hours, minutes or seconds ) , my research suggests this maybe an over current protection , or leaky/faulty LEDS , or a bad LED driver circuit . So I opened it up , stabbed my Multi Meter on its Backlight outputs and put peepers on the caps , hoping to see something . Caps look fine , no sign of shorts or open circuits on the caps , though I am no electrical engineer . I visually inspected the backlights, they all illuminate uniformly and temporarily blinded me in the process

The single board contains both hot and cold , power and brains of the set . There is no markings to indicate the designed Backlight LED output voltage, though this is measured as 112V in total , or 56V on each of the two rails . The voltage is very stable until it weirdly goes off and drops to half .

On a side note , I blindly guessed that this is a board problem . I did find replacement boards on Evilbay ( with same model and physically identical) , though to my dismay these boards are re-used across many (Vestel) white label brands and have different firmware and do not work correctly I tried

[Diah]

Re: Crappy Vestel Set Backlight going off randomly

so this boards photo the original one??
if yes. you need to re solder the transformer with white cover and the small yellow one too.

re solder them from up side and down because this boards sandwich and the big transformer missing 2 poll soldering at the top side which facing the small yellow one.. as i see from the photo.

[90Ninety]

Re: Crappy Vestel Set Backlight going off randomly

so this boards photo the original one??
if yes. you need to re solder the transformer with white cover and the small yellow one too.

re solder them from up side and down because this boards sandwich and the big transformer missing 2 poll soldering at the top side which facing the small yellow one.. as i see from the photo.

Hey Chief

Yeah the board is the original, I have another and its also missing solder on the top side pads .

I did already reflow the back of the board , which actually decreased the intermittency of the failure , so you may be onto something

[dskall]

Re: Crappy Vestel Set Backlight going off randomly

https://www.youtube.com/watch?v=3eTI...chaelDranfield

[90Ninety]

Re: Crappy Vestel Set Backlight going off randomly

https://www.youtube.com/watch?v=3eTI...chaelDranfield

The LED strips on mine are connected together via wires , I wish I had taken pictures .

Couldn't see any problems , I did reseat the connectors on each strip

[90Ninety]

Re: Crappy Vestel Set Backlight going off randomly

So

I have been studying this further . What I have found , is that there is a pattern as to when the backlights are switched off .

If unplugged from wall , or without AC , the set can be plugged in then turned on and will work for hours without problem

If left plugged in and when used for many hours (maybe also when left in standby) , eventually the backlights will only come on for several seconds .

I put a meter on the LED terminals on the board . The voltage drops off , even when there is no LED strips plugged in ( when TV has been on for hours prior )

I am still thinking it is a board problem , since the voltage drops to half , with or without the LED backlights connected . However I suppose there is a chance that a thermal cut out component is triggered after a certain time when the backlight is connected , then remains triggered until fully cooled down?

Perhaps I should try replacing the capacitors , that are in the circuit with the LED strips , their capacitance is ok but perhaps they have faulty ESR?

Where should I start with the board ?

[CapLeaker]

Re: Crappy Vestel Set Backlight going off randomly

Turn the backlights way down like 40 to 50% and see if the backlights stay on.

[90Ninety]

Re: Crappy Vestel Set Backlight going off randomly

Turn the backlights way down like 40 to 50% and see if the backlights stay on.

I tried this , though simply putting it in standby for 10 minutes or more , provides a workaround , after this the TV will work seemingly fine for 12 hours or more .

Though since the problem is intermittent , it is a pain to diagnose , since the problem only occurs after much time is passed

Had this TV opened more than a brass drawers now

[90Ninety]

Re: Crappy Vestel Set Backlight going off randomly

After some further restarts it has been on now for almost 24hours

When it works its only slightly warm to the touch , however I noticed before the backlight goes out , the centre of the LCD panel is hot .