Blaupunkt 49/235z Backlight Inoperative

[Bloopeta]

Blaupunkt 49/235z, got this TV described as sound no picture, had a quick look, and backlights came on at first, but the LED inverter was buzzing very loudly, left TV on and after around 20 mins the backlights went out. Turning TV off and back on would bring them back on for a while but always went off sooner or later.

I stripped the TV right down, tested the LED strips, both as strips and single LEDs and all of them illuminate with tester.

I took readings from PCB for LEDS, which were
LED+ 231v (when backlights were illumiated)
LED+ 132v (times when LEDs had gone off)

As mentioned when LEDs where illuminated, the inverter was very noisy and loud, when the LEDs wont come on, this is silent.

Other readings from PCB are -

+12v 12.40v
SGND
+5v 5.21v
+5vSB 5.22v
PSON 4.38v
SGND

+12v 12.40v
BK 5.19v
ADJ 4.66v
SGND

[Bloopeta]

Re: Blaupunkt 49/235z Backlight Inoperative

Am I looking at a PCB? As they are very cheap for a replacement, wouldnt be worth repairing the board at all.

[budm]

Re: Blaupunkt 49/235z Backlight Inoperative

Did you try lowing the backligts level down as low as possible to see if the backlights will stay on longer (if you are able to keep it on long enough to get to the settings)?

[Bloopeta]

Re: Blaupunkt 49/235z Backlight Inoperative

Did you try lowing the backligts level down as low as possible to see if the backlights will stay on longer (if you are able to keep it on long enough to get to the settings)?

Yes put them on low as possible, it did stay on for a good while at first, but lat time I tried wouldnt come on at all

[CapLeaker]

Re: Blaupunkt 49/235z Backlight Inoperative

Bad backlight leds...

[Bloopeta]

Re: Blaupunkt 49/235z Backlight Inoperative

Bad backlight leds...

Even though Ive tested them all??

[budm]

Re: Blaupunkt 49/235z Backlight Inoperative

Even though Ive tested them all??

How much drive current did you test them at? 200 ~ 300 mA?

[Bloopeta]

Re: Blaupunkt 49/235z Backlight Inoperative

How much drive current did you test them at? 200 ~ 300 mA?

Tested them with LED tester as previously advised on here. as in, they all lit up.

Is there another way to determine which, if any are faulty please?

[Bloopeta]

Re: Blaupunkt 49/235z Backlight Inoperative

Anyone?? When I turn on TV they all illuminate, but then all go off after a while, if I illuminate the LEDs as strips or singular, they all seem to work.
If I turn TV off and back on, they illuminate again
What can I do to find out which ones are at fault??

[dick_barton]

Re: Blaupunkt 49/235z Backlight Inoperative

As already said by others it looks like a led problem. Led testers don't test the leds at full current which is why led testers can operate the led strings. Post #8

[Bloopeta]

Re: Blaupunkt 49/235z Backlight Inoperative

As already said by others it looks like a led problem. Led testers don't test the leds at full current which is why led testers can operate the led strings. Post #8

Thanks for the reply, so is there a way I can test and determine which LEDs are at fault please?

[diif]

Re: Blaupunkt 49/235z Backlight Inoperative

Thanks for the reply, so is there a way I can test and determine which LEDs are at fault please?

If you don't have a current limiting power supply you can use a pair of AA batteries as in this thread https://www.badcaps.net/forum/showth...ght=AA+battery

[Bloopeta]

Re: Blaupunkt 49/235z Backlight Inoperative

If you don't have a current limiting power supply you can use a pair of AA batteries as in this thread https://www.badcaps.net/forum/showth...ght=AA+battery

I will give that a shot and let you know the results.

At present Ive had them running as normal for 25 mins and they havnt gone out as yet, so just waiting to see how long it will take for it to go off again

[budm]

Re: Blaupunkt 49/235z Backlight Inoperative

What is the DC Voltage when you measure it between the two wires of the LED connector (Connector still in place)?

[Bloopeta]

Re: Blaupunkt 49/235z Backlight Inoperative

What is the DC Voltage when you measure it between the two wires of the LED connector (Connector still in place)?

At present, whilst all LEDs are illuminated, 229v

[Bloopeta]

Re: Blaupunkt 49/235z Backlight Inoperative

Ran for 58 minutes before went off, once off is putting out 138v.
Turned off and back on again, and ran for less than a minute before they went out.
Turned off and back on again, all still illuminating, but goes off pretty much straight away, now when try to turn on and off they just flash on for a milisecond and go straight off

[Bloopeta]

Re: Blaupunkt 49/235z Backlight Inoperative

If you don't have a current limiting power supply you can use a pair of AA batteries as in this thread https://www.badcaps.net/forum/showth...ght=AA+battery

Have now tried, with a pair of AA batteries, all LEDs illuminate, and im now partially blind lol

[vinceroger69]

Re: Blaupunkt 49/235z Backlight Inoperative

Ran for 58 minutes before went off, once off is putting out 138v.
Turned off and back on again, and ran for less than a minute before they went out.
Turned off and back on again, all still illuminating, but goes off pretty much straight away, now when try to turn on and off they just flash on for a milisecond and go straight off

possibly something heat related but what? is a new power supply cheap? maybe worth ruling it out you could always resell the board on ebay etc and get your money back if it does not fix the issue

[Bloopeta]

Re: Blaupunkt 49/235z Backlight Inoperative

possibly something heat related but what? is a new power supply cheap? maybe worth ruling it out you could always resell the board on ebay etc and get your money back if it does not fix the issue

Ive actually swapped out the PSB this morning as I picked one up for pennies, just to rule it out, no change

[vinceroger69]

Re: Blaupunkt 49/235z Backlight Inoperative

Ive actually swapped out the PSB this morning as I picked one up for pennies, just to rule it out, no change

sounds like a led issue then maybe a led failing when hot if thats possible, are all the led strips the same number if so maybe buy one strip and swap each strip in turn?