Tv repair ? Back light gone

[angellonewolf]

Ok our tv back light has gone you can see the screen has a picture by using a torch to see the picture

I've taken apart the TV and hope I've not broken the main screen was very carefully removed


But I'm using my meter and can't seam to get any readings through the leds them self's

Any body want to help out where to put my meter probes to cheak the leds out one by one ?

 

[mike 109444]

Are you sure it's the led's and not the driver board ?
There are lots of YT vids on led tv repairs and might even be one on your model

 

[angellonewolf]

ive spent a bit of time on the net ive tested the power supply and it outputs 67v on both channels so im summing thats normal

ive looked on line you casn get a led tester for £20 quid on the bay of thieves but ive also cheaked out the price of the new led strips and for my tv there £60 quid for a set if they where 25 ish mark id throw a set in but at the cost of 60 and then the led tester thats a fair bit of money to the new tv

we where using this 55 inch and its only 3 years ish old so no time at all realy but i had said if we see a 65 or 70 we do an upgrade

if i can get this working for the cost of a led and resolder it in id keep it in a bedroom or such when we upgrade

 

[gaz1]

as already stated its normally the driver board thats fails with them usually caused by over heating issues

users also can cause issues by having the back lights too bright

 

[angellonewolf]

from my looks online they seam to say a failed led is normaly the problem(as the leds are in series as if one fails the whole line drops out ?) as if one goes out the protection curcit turns off the power to the rest to protect the rest ?

 

[Kram]

LED's fail open circuit, if one blows the rest wont get power. Usually visibly discoloured before they blow.

ive spent a bit of time on the net ive tested the power supply and it outputs 67v on both channels so im summing thats normal

Be aware that 60v is about the maximum safe voltage and anything much higher can give shocks, so needs some care, if your not used to electrical repairs.

You dont need a LED tester, a current limited adjustable boost coverter will let you check them. A few pounds of ebay, then plug it into any 12v supply or battery.

From the pic you have 4 strings in series, 7 led + 8 led + 7 led + 8 led, 30 LEDs in total.
67v seems quite low as white led's are usually about 3-3.5v, I'd be expecting nearer 80-100v.

67 / 30 = 2.225v each, far too low for a white led (unless theres some new LED tech Im ot aware of!!)

Id disconnect each string to test seperately, if one doesnt light up then test each led at 2.8-3v.. So for 7 led have it set a maximum of 21V and 100mA. For 8 led, 24v.


Check the driver board pcb. Often if theres no signs of obvious overheating, it will be the power supply capacitors have failed. I have replaced a few.

 

[angellonewolf]

LED's fail open circuit, if one blows the rest wont get power. Usually visibly discoloured before they blow.


Be aware that 60v is about the maximum safe voltage and anything much higher can give shocks, so needs some care, if your not used to electrical repairs.

You dont need a LED tester, a current limited adjustable boost coverter will let you check them. A few pounds of ebay, then plug it into any 12v supply or battery.

From the pic you have 4 strings in series, 7 led + 8 led + 7 led + 8 led, 30 LEDs in total.
67v seems quite low as white led's are usually about 3-3.5v, I'd be expecting nearer 80-100v.

67 / 30 = 2.225v each, far too low for a white led (unless theres some new LED tech Im ot aware of!!)

Id disconnect each string to test seperately, if one doesnt light up then test each led at 2.8-3v.. So for 7 led have it set a maximum of 21V and 100mA. For 8 led, 24v.


Check the driver board pcb. Often if theres no signs of obvious overheating, it will be the power supply capacitors have failed. I have replaced a few.

Now that you say 67 is low I did see on the leds strips something about 94v some where

 

[500e]

Say sorry to @gaz1

 

[Kram]

The 94V-0 is a confusing and common mark seen on most PCB's, its a UL flammability rating that means the part will not burn for more than 10 seconds or something. Its not related the the led voltage! Terrible name for it!

 

[500e]

All LCD/LED TV Backlight Voltage Details With Images » Teckwiki

Hey Technicians, How are you? I hope you will be fine. So today we are going to share the latest and a very useful topic for every technician who repairs

www.soft4led.com

May help

 

[angellonewolf]

Say sorry to @gaz1

The 94V-0 is a confusing and common mark seen on most PCB's, its a UL flammability rating that means the part will not burn for more than 10 seconds or something. Its not related the the led voltage! Terrible name for it!

I will get a pic of the board and hope you can point out the capacitors to cheak they all look ok not burnt but I know that they don't always blow

 

[angellonewolf]

All LCD/LED TV Backlight Voltage Details With Images » Teckwiki

Hey Technicians, How are you? I hope you will be fine. So today we are going to share the latest and a very useful topic for every technician who repairs

www.soft4led.com

May help

And typically they don't do tcl tvs

 

[Onoff]

I will get a pic of the board and hope you can point out the capacitors to cheak they all look ok not burnt but I know that they don't always blow

Look for swollen/domed capacitors rather than "burnt".

 

[angellonewolf]

ive looked it all looks brand new

 

[mike 109444]

As with most items like the led strips the tv makes buy them in so other tv makes use same part. If you google "e469119" (part number on the led pcb you will get a lot of hits like this https://www.ebay.co.uk/itm/33463049...=5338956825&toolid=10049&customid=777_777_777
From that you can see further don that listing the tv's that the strips are used in. As most tv's will drive the led's at about the same voltage it should be possible to find a tv of same size and probable with same driver using that set up. Then you can use the info from that link in post #10 as a guide.
I could not use the link from post #10 as my antivirus did not like it !

 

[angellonewolf]

 

[mike 109444]

link to testing e49119 strips

 

[angellonewolf]

All the capacitors look ok

 

[angellonewolf]

link to testing e49119 strips

Off out this morning see if I can have go with a battery later

And now got to work out the poss and negative areas as well

 

[angellonewolf]