LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

[nomoresonys]

I was correct about needing a reflow, I am also correct by telling you it will last a lot longer if you can get a fan blowing on the IC.

[Seb932]

Short Update - TV is working again. BGA Reflow of IC100 does the trick.

Long Story:

• PWS,Edgelit,T-Con,Panel was working (checked before)
• Previous missing voltages, all voltages are there, but my measurment method wasn't correct. I've partly measured directly on the IC output, which is before the LC part => I've measured the direct output frequency without smothing...🤦
• All voltages on MB are correct, no further ideas beside BGA reflow
  • start with IC100
  • stipped down plastic parts from MB
  • removed the metal cover
  • Heatgun from below ~350°C
  • Heatgun on top of IC100 max 550°C
  • started with preheating to 200°C both sides
  • followed with a short period of maximum temerature on top of IC100
  • slowly cool down
• put everything together
• Power on => Everything is working 👍

I know, this is not a final solution, without proper reballing the chip will fail again at some point of time. The TV will be used as backup, so no worries. Maybe I will find someone who is able to do reballing.

Thanks for your help!

[GORS]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

What is the final outcome of this thread? I have the same TV with the same problem (at least it looks that way).
So I would like to know the root-cause of this and see if it could help me with mine…..

[nomoresonys]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Thought as much, that was just for those that might see this and be wondering how to check it, sometimes it's hard to tell exactly where a noise is coming from.

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Might have a bad solder joint somewhere, those will also cause a buzz.

buzz is already gone by replacing/bridging the burned choke, remvove the bridge buzz is coming back

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

log capture use TTL adapter 3.3V level and any terminal to capture the log
for waking up.. plug USB mouse and another USB stick you put on it root any MPG4 movie , start moving & clicking on mouse left and right while you plug the tv in wall socket

Thank you very much! I've an 8ch logic analyzer on hand, should be possible read JTAG as well. But need some time...

[nomoresonys]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Might have a bad solder joint somewhere, those will also cause a buzz.

[nomoresonys]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

When you hear an unusual buzz, you need to use a stethoscope or rubber hose or such to try and pinpoint where it's coming from.

[Diah]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

log capture use TTL adapter 3.3V level and any terminal to capture the log
for waking up.. plug USB mouse and another USB stick you put on it root any MPG4 movie , start moving & clicking on mouse left and right while you plug the tv in wall socket

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

good, then you should be able to capture the start log via JTAG.. its maybe the MB in protection mode like OLED one... just with USB mouse and USB stick with media content on it waking it up

Ok, will try. Any tutorial how to do this?

[Diah]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

yes, tested and working => 5V normal/USB are supplied by IC2304

good, then you should be able to capture the start log via JTAG.. its maybe the MB in protection mode like OLED one... just with USB mouse and USB stick with media content on it waking it up

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

by the way do you have 5V USB?

yes, tested and working => 5V normal/USB are supplied by IC2304

[Diah]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

by the way do you have 5V USB?

[Diah]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Done already. eMMC Voltage is also correct =>3.3V. Still missing 1.0;1.2;1.5V...

keep it on, and monitor the temp of MB, if u have warm camera will be good.. there should be part will warming out

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

jumper it and let the game start... other wise buy replacement MB

Done already. eMMC Voltage is also correct =>3.3V. Still missing 1.0;1.2;1.5V...

[Diah]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

jumper it and let the game start... other wise buy replacement MB

[Seb932]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Need to give a correction, the burned choke is input for 1.2V voltage regulation, not output.
If I short the choke the buzzing noise is gone, but still this fancy PWM signal on output side...

The choke doesn't just burn out, you have a short somewhere, unsolder the choke and measure the resistance on each side relative to gnd.

No short measureable, also the 12V input is stable. Maybe its burned during some of the tests before. Because the buzzing noise i've recognized first during the test in #18

[lotas]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Tried to find L2302 to check eMMC V. During search I found L2322 is burned (resistance 440Ohms), which is output for 1.2V

Is it ok to bride the coil for testing purposes or better replace with some other SMD coil?

The choke doesn't just burn out, you have a short somewhere, unsolder the choke and measure the resistance on each side relative to gnd.

[Diah]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Tried to find L2302 to check eMMC V. During search I found L2322 is burned (resistance 440Ohms), which is output for 1.2V

Is it ok to bride the coil for testing purposes or better replace with some other SMD coil?

you have one ceramic cap shorted... other wise this filter coil will never burning.. good found

dont bridge it unless you find the short

[nomoresonys]

Re: LG 49UB850V not switching on / standby LED off / LD701 blinks 5x

Sure bridge for testing.