Visio VO47LFHDTV10A has power, no backlight

[Kylum]

Hello, I am in need of some assistance. My best friends LCD tv wouldn't turn on after turning it off one day. Since I have has luck on fixing tv's and other electronics in the past he brought it to me. It powers on. Logo goes from amber to white like it suppose to.

First, thing I did was open it up and found some bulging caps.( as expected). One on the PSU of the 24v supply and the two caps on both of the master and slave inverter. I replaced all 5 caps. Now when I was just about to unsolder the first cap on the master inverter I noticed that there was a solder ball on the 32pin IC chip. It was between around pin26 or pin27. I removed it and proceeded with the caps. Still no backlight.

So then I decided to test the voltage at the PSU. I found there was no 24v output from the PSU. After I while of probing the PSU secondary that seems to have good caps resistors and caps, I then unplugged everything from the PSU and tested again for voltage. Bam, 24v was present. One by one plugging in each plug back int the PSU. I discovered that with the slave inverter pluged in I don't get 24v. With it out I do. However there is still no backlight from the master. I then tested the pins of of the masters and found that I'm not getting 5v for the inverter power on. It's only 3v. I then went straight to the main board tested pin 13 on the connector and it was at 3v also. Following the trace from pin 13 I come to a smd resistor r24 and a electrolytic cap ce28. I have not tested the cap yet but it does have voltage to ground. That and I only have a cheap extech with no capacitance. I'm getting 5v on the resistor leg not connected to the cap and 3v at the leg that is connected at the cap. What shouild the resistance be on this resistor? Should I gust replace the cap and see what happens? I think the resistor is bad since it has a very low resistance of under 1k. Could I just jumper this resistor to test if the backlight comes? How to test the ic chip since there was a solder ball on the legs and it might be bad?


Thanks in advance. I will post some pictures when I get home

[tom66]

Re: Visio VO47LFHDTV10A has power, no backlight

3V is fine for BL ON on these sets.
You should check the inverter hasn't got any failed FETs.
And that solder blob? Did you remove it?

[Kylum]

Re: Visio VO47LFHDTV10A has power, no backlight

Yes the solder ball was removed before I replaced the caps on the inverter. It wasnt a solder bridge. I was able to remove it with a pair of tweezers. I will try and test the inverter some more when I get home but its my birthday and I know the wife has something planned so it won't be until tomorrow.

[budm]

Re: Visio VO47LFHDTV10A has power, no backlight

There are more than one version and brands of the boards used in this TV.
http://www.shopjimmy.com/catalogsear...=VO47LFHDTV10A

[Kylum]

Re: Visio VO47LFHDTV10A has power, no backlight

Here are the boards in this tv.
Main:3467-0072-0150
Master:6632L-0392a
Slave:6632L-0393a
Pay:0500-0510-0340

I figured out that if I unplug the ribbon cable from the slave the voltage for BL_ON goes to 5v. Not sure if that matters or indicates a short. I tested the FETs and there is only 24volts on the input pin. There is no output voltage coming from IC. Also the input voltage to pin27(UVLO) is 2.7v. Is 2.7v here ok or should it be 5v?

I'm assuming that I need to replace the IC's on both the master and the slave at this point but I'm not quite sure

Thanks for the help guys

[tom66]

Re: Visio VO47LFHDTV10A has power, no backlight

Are these the LG Master-Slave inverter design?

[Kylum]

Re: Visio VO47LFHDTV10A has power, no backlight

Yes sir they are.

[tom66]

Re: Visio VO47LFHDTV10A has power, no backlight

Are those capacitors from RadioShack? They do not look like low esr type which is essential for a power supply or inverter.

[Kylum]

Re: Visio VO47LFHDTV10A has power, no backlight

No i didn't get them from radio shack. I actually have a bin full of pulled caps and resistors. Just so happened to have the same size ones in the bin. I plan on getting ESR type caps if and when i figure out what else i will need for this TV. Mouser is local for me but not close enough to make trips back and forth every time i need something. However if i need to order the inverter IC's i will have to order them form digikey or ebay as mouser does not have them in stock. Just trying to order the least amount of times as possible.

I really appreciate the fast response. thanks

[tom66]

Re: Visio VO47LFHDTV10A has power, no backlight

Typically the light blue lelon are not suitable replacements.
You can order caps from Digikey, no minimum order and $3 shipping. Or other suppliers.

[Kylum]

Re: Visio VO47LFHDTV10A has power, no backlight

I am only using those for testing before placing an actual order where i will order the correct low esr caps. Im trying to find out what else is wrong with the inverter first

[Kylum]

Re: Visio VO47LFHDTV10A has power, no backlight

So is there a way for me to test the IC# BD9897FS to see if it is working properly?

[Kylum]

Re: Visio VO47LFHDTV10A has power, no backlight

Well it looks to be that pin 27 of the Inverter IC is shorted to ground internally. This is on the master. I tested it on the slave and it is not. So I decided that one if not both IC chips are bad. I found a full kit on eBay and they just happen to be a local shop that is around the corner from the house for only 15 buck. Actually a few buck cheaper than going through digikey + shipping. I will post back once I get around doing the job plus I can't find the correct nozzle for my hot air rework station so I will have to wait to get that in the mail as well.

[Kylum]

Re: Visio VO47LFHDTV10A has power, no backlight

Update:

IC replaced on the master and still the same issue. I can't seem to find the problem. I would really appreciate some guidance on what to do from here .

Thanks

[tom66]

Re: Visio VO47LFHDTV10A has power, no backlight

I would consider replacing those Lelon caps with the proper required replacements. Also, look at the slave, consider if the chip on there is bad too.

[Kylum]

Re: Visio VO47LFHDTV10A has power, no backlight

Sorry, I forgot to mention that the caps have been replaced with the ones in the kit. I have considered that the slave chip might be bad also. However, I was under the impression that the master would still turn on with out the slave board plugged in. I read that if the slave is bad the master will still work, resulting in only have the display lighting. Or am I wrong about that?

Here is a link to the kit
http://www.coppelltvrepair.com/p/68/...-other-lcd-tvs

[tom66]

Re: Visio VO47LFHDTV10A has power, no backlight

Depends on the configuration. At the very least you'll usually get a flash of light (less than a second is typical, but in some cases a 2~3 second glow.) It doesn't usually stay on.

[Kylum]

Re: Visio VO47LFHDTV10A has power, no backlight

Ok. I will check that again but I'm about 99% sure that there was absolutely no flash or glow at all. I think that I'm loosing voltage that turns the IC on but I'm not quite sure. I know that I'm getting 24v,5v, and 3v at the connector coming from the PSU. @ the IC I'm only getting 24v on pin 26 and 2.7 v on pin 27. With no output voltage to the fets on there appropriate pins.

Thanks for being patient with me Tom66. I'm still learning.

[budm]

Re: Visio VO47LFHDTV10A has power, no backlight

What voltage do you get at DIM pin?

[Kylum]

Re: Visio VO47LFHDTV10A has power, no backlight

I will have to get home to test that. This might be a dumb question but which is the DIM pin? The pinout doesn't say DIM so I'm a little lost. I would assume its less than 1v since I'm only getting voltage @ UVlO pin 27 and VCC pin 26. All other readings are in mV. I will have to retest to verify that though. Go easy on me I'm still a noob.