LG55UB850V no picture or audio - flashing LED's help please?

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

good work.. LD1900 lit on when there are video signal go to LVDS

did you look on the screen if there picture complete? if not
the slight voltage fluctuation at F1 and the buzzer sound you hearing much high caused by one bin or more cut or moved to aside at ribbon cable. if you saw the picture on screen fine then they are fine. but could be the LVDS cable.

BTW: the area you heat it are the DDR

[nomoresonys]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Probably wouldn't hurt to update the firmware if it will stay on long enough.

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

good work.. LD1900 lit on when there are video signal go to LVDS

did you look on the screen if there picture complete? if not
the slight voltage fluctuation at F1 and the buzzer sound you hearing much high caused by one bin or more cut or moved to aside at ribbon cable. if you saw the picture on screen fine then they are fine. but could be the LVDS cable.

BTW: the area you heat it are the DDR

Thank you for the picture and clarifying those DDR chips, that is helpful.

Sadly the picture is not good now. Well, partly good.

When turn the tv on from standby, during the 3 flashes of the front red status LED, the screen turns on. I get 2 seconds of correct screen display, and no buzzing from T-Con board, followed by 2 seconds of slightly darker screen with visible blue grid lines, accompanied with buzzing from the T-Con board.

This cycle repeats over and over.
First 2 seconds good, then 2 seconds bad. This also coincides with the voltage fluctuation. During the 2 seconds good, the voltage has fluctuated to highest value of 11.58v, then during 2 seconds of bad, the voltage fluctuates down to lowest value of 11.48v

If I unclip either of the T-Con screen ribbons and try again, there is no buzzing.

With T-Con screen ribbon nearest the power supply board unclipped, there is no buzzing from the T-Con board, and I get a STEADY 11.74v reading constantly at F1.

With T-Con screen ribbon nearest the main logic board unclipped, there is no buzzing from the T-Con board, and I get a STEADY 11.66v reading constantly at F1.

Here is a video showing what the screen is doing

https://photos.app.goo.gl/fPPp3ZkXdQWy6eag8

So this is a new problem which I didn't have before heating up the DDR chip/s.
Do you think the heating process has caused this new problem, or just coincidence and unrelated?

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

i would inspect the both ribbon cable under enough light with good loop to see if one of the pins contact get missing or moved to side... same way to the LVDS.. am sure you will find the issue there.

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

i just saw the video.. if your inspecting the ribbon and LVDS complete and they are in good condition... then you have parts pulling currect on the MB. maybe the WIFI module.. disconnect and check.. or when you did heating. one small SMD part went missing or disconnected. much one filter.. thanks god you took photos to MB so you can compair if one SMD part went missing

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Well I've had the magnifying glass out and a good light source and inspected the LVDS connectors at mainboard and T-Con board, cable contacts at both ends of the LVDS cable, and the ribbon contacts at the T-Con end of the screen ribbon cables. All looks ok, no missing or damaged contacts anywhere. All 8 of the LVDS pins (51 - 44) that carry the 11.48 - 11.58v to the T-Con board have continuity to the corresponding pins on the T-Con board LVDS connector.
Regarding the voltage, 11.48v should be ok as this is within 5% of the 12v yes?

If perhaps like you say, a small SMD has taken heat damage from heating around the DDR chips, I will need to remove the soft grey rubber pads and also the white heatsink pad from above the DDR chips in order to check. I assume this is held down in place on the board by the blobs of grey silicon at either corner, and the white heatsink has thermal paste on the underside.
I will post a picture after removing this as other than something showing visual signs of overheating, I'm not sure how to tell if any of the small SMDs are damaged. Can each one in that area be tested with a DMM?

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

I'm not sure how to tell if any of the small SMDs are damaged. Can each one in that area be tested with a DMM?

you don't have damaged parts so its impossible to testing the smd parts.

before all you need to measure the 5.V rail on any USB post to check if its stable or not. if yes then ....

now you are sure all ribbon and LVDS in best shape, this is most important.
the issue now caused by heating. THE HEATING will be the only cure method.

moving the air heat gun over the surface not good idea with out masking the parts on the area.
after you take out the rubber and the heatsink use adhesive painters Tape to mask the DDRs and all smd parts around tight to the boards. then start reflew with yours gun.. one things need be aware, the angel of the gun should be 90° always facing the boards so the air pressure will be used to stick the parts at it place with help the masking tape.

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

OK so I have attempted with the heat gun after masking off various areas. I have been unable to improve the current situation however It has not made anything worse, but exactly the same condition is still present - 2 seconds good screen followed by 2 seconds bad with slightly darker image and lines and buzzing, and keeps repeating this cycle.

I am getting a stable 5.11v at the USB ports.

Could it be that the T-Con board has suffered some sort of electrical damage as a result of the various testing procedures I have tried?
Is it worth checking the 2 screen ribbon connectors at the panel side - it looks like lots of screws around the outside of the screen would have to be removed in order to going access to these?
Frustrating as I know the screen was perfect when I first started troubleshooting, and the TV was working briefly for a day before the screen started not turning on etc.

EDIT: Even before trying the heat gun again, I've noticed no light coming from the optical audio port during standby, or during screen on and tv powered up. I'm not sure at what point during the last couple of days this stopped lighting up.

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

5.11V on usb are high to me.. while yours DMM always read little less the original V. for example when you disconnect one ribbon buzzer stop and F1 start to read 11.74v. this why need to do exactly this points
1- disconnect one ribbon to let the buzzer out..F1 stable V. messure yours USB port become less than 5.11V.

2- you need with out thinking twise remove make free access tp the panel buffers boards.. to clean them with brust .. you are putting the tv face on yours bed. who knows what went inside the tv... hair can cause issue too. this why need to clean it.

after this 2 points if no change we can run hardware test on MB.

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

OK so I disconnected one ribbon, stable voltage at F1 11.74v, no buzzing, measurement at each USB port is 5.116v still. Same when removing other ribbon. Even when both ribbons removed, still 5.116v at each USB.
Same when LVDS cable disconnected from the mainboard, still 5.116v at each USB port.

Access to the other end of the two ribbon cables was much easier than I thought it would be. Removed the metal covers and visual inspection of that end of each ribbon cable showed no signs of issues with pins on ribbon, or any issues at connectors. Re-seated each one and reconnected everything, but no change in behaviour. Dusted ribbon ends and connectors to ensure 100% clean.
No change.

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

did you cleaned the 2 boards along the screen left & right ?
take out your MB from the TV and work on table.. upload focused high resolution photo to the area i marked RED Color. if you are not able to track hardware measurements then MB in place and tv on you monitor F1 V while you heat with Hair dryer the blue area only

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Yes I checked the long left hand and right hand panels when checking the ribbon connectors and all looked fine, no hairs/dirt or anything at all, completely spotless.

I removed the main board and took some pictures as requested, hopefully they are clear enough. I have also reconnected the board so I can measure as suggested the voltage at F1 while heating the area that you marked out in blue. This unfortunately made no difference. The heat setting was 2 out of 3 on the hair dryer so not as high as my heat gun but should be hot enough to try to show a difference by heating that area. The voltage reading didn't change from the fluctuating figures from before.

Can I ask what you mean when you say 'if you are not able to track hardware measurements' please?

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Can I ask what you mean when you say 'if you are not able to track hardware measurements' please?

using DMM testing SMT/SMD parts not easy matter. users used to replace complete boards. but i would like to help and narrow the things to you as i am now have yours MB under my hands.

the critical parts at panel_Vcc 12V. i remarked them to you. the most parts could effected by heating are C with low uf. such 0.01uf / 0.1uf /10uf

also the transistor NPN one could leak. so all what i marked need to measure them with yours DMM.while the set out from wall socket .. if you don't know how just ask. if i am not here of sure other will help you too.

EDIT: this Coil Filter 2R2 for reduce Noise to my poor eyes are damaged by heat see photo 2R2

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Part 2 EDIT:1.0V VDD circuit really effected by hot air pressure.

C2348 22uf 10V moved from it place , C2312 2200pf 50V, C2314 0.1uf 16V

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Thank you Diah. I will aim to test all of the components which you have marked in red outlines on the pictures.

My DMM can measure a range of 10nF up to 100uF so should be fine. I have never measured SMD capacitors before, or attempted to remove/replace one.

Measuring them in situ on the board would not give the correct reading as there will be other components on the board that would affect the readings - is that correct?

Is it worth checking each ceramic SMD capacitor for short circuit while fitted to the board? Can this be done in situ while on the board by checking each side of the capacitor against a ground point on the board? Or would this not work if they all use different a ground plain within the board?

This is all new to me but I am enjoying learning and enjoy troubleshooting so hopefully we can narrow down or pinpoint the issue

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

my post #74

first things you need to do soldering C2348 22uf 10V at its place. who knows could be the reason. other caps i don't think there short. just need to put the soldering iron on the each side to stick them in place in case they are to your eyes not correct soldered

EDIT: 99.9% yours issue this 2 caps .. need to solder them in place

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Thank you. I can see what you are saying about those caps, especially C2348, as it appears in the photos like it is either mis-aligned or not making proper contact at one end. I have checked back through my photos and this C2348 was exactly like this when I took the back off from the tv for the very first time before I touched anything, so it hasn't been moved or affected by heat or anything I have done. Perhaps it has always been like this since manufacturing of the board...

Regardless, I have tried to heat it with soldering iron and solder to straighten it up on the board slightly, but it doesn't want to move. I wasn't able to straighten it up or remove it - I had hoped I could remove it to test it before re-soldering it back on straight to the board. Feels almost glued to the board after heating both ends carefully - zero movement. So I have just applied a bit of extra solder in order to try to ensure a good contact / reflow at either end.

I have done the same with the other 10uF caps around that area in case of a bad solder joint, but while reflowing I didn't spot any cracks. If there were any that were too small to see under magnifying glass (smaller than hairline), then hopefully the reflow on each side that I have done might help.

I don't know if it is possible to test the NPN transistor you highlighted in red?

I have been unable to try any reflow on any of the smaller 0.1uF and 2200pf caps as my iron tips are not small enough for that sort of delicate work. My eyes would struggle also! I used flux and you can see the ones that have been soldered as they have some additional solder on the ends now, but I made sure there were no shorts anywhere or any new damage from the work I carried out.

After all of this, still the exact same symptoms

I tested every cap on the board front and back to see if each one had a ground side. Most of them did have one ground side.
Some of them didn't 'appear' to have a ground side at all - 20 of the SMD caps on the front of the board to be exact - but they must, so I assume those ones must use a different ground plain to the one I was using to test.

More interestingly, I did notice one cap (C6702) on the back of the board down near the aerial input module which showed ground on BOTH sides - is this a definite shorted cap?



Also, it may be irrelevant, but I've pinpointed the source of the actual buzzing noise on the T-Con board (not the 'cause' though) - the buzzing is coming from one of the SMD caps - C235



This is probably just reacting to the incorrect or fluctuating voltage it is receiving (?) but this is 100% the cap that is buzzing. Don't know if this is helpful or not.

Finally just before taking a break from things (for my own sanity) I tested the voltage at the LVDS connector on the mainboard, on pins 51-44, the voltage also fluctuates the same as it does at fuse F1 on the T-Con board. I then traced this back further, to the main board power connector, and this too fluctuates in time with the buzzing.
Finally I traced back to the power board, which as you will remember used to be a stable voltage at both J71 and J75 - this is also fluctuating with the buzzing/screen issue:

24.12v up to 24.16v J75, fluctuating every 2 seconds
11.77v up to 11.79v J71, fluctuating every 2 seconds

So way back when the initial problem of the screen not turning on was happening, these voltages were stable.
Since the heating of the main board which cured the screen not turning on, this new problem of the T-Con board buzzing every 2 seconds, and the screen picture going brighter and darker with lines, every day seconds, along with T-Con buzzing, has come about.

Does this mean that attention should be turned to the power board now, or is this fluctuating voltage present here just a 'symptom' of the problem which is either on the main board or possibly even the T-Con board?

If I unplug ANY one of the 3 connectors on the T-Con board, then I get stable voltage throughout the boards.

[nomoresonys]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Well test that c235, test it in diode mode, then in ohm mode, tv unplugged, unplug everything from tcon then test it, then test it with just the panel unplugged, then test it with everything hooked up, still with tv unplugged from power.

[Diah]

Re: LG55UB850V no picture or audio - flashing LED's help please?

i am confused how it come the 2 caps as you said they were like that before. however we do have 2 photos 1 they look aligned in place and the 2 absolute moved.
another matter you didn't explained about the Coil Filter 2R2 close to them.. did it top shape was also so !!
let say yes. you are right. you applied heat while the set ON and you stooped after LD start to lit on. i wrote before yours set didn't complete the boot. this why we don't have panel_VCC on F1 high. the heat just glitch it to complete the last boot steps. tv turn on. but like clock each 2 seconds there are some where at booting steps try to jump .. this is may calculation it may wrong too. but i think deeply your issue at MB .. unless the heat spike signal to effect the main chip of T-CON. this why when disconnected one ribbon the noise out and the panel_VCC stable.

finally. i would suggest you.
first right now remove the wifi module... you can later plug it in when every things correct
second before you did pressed the rest micro switch on the MB. so check them if one of them remain pressed. you can do it with yours DMM peep ton when you press it should peeped then if they are both fine turn on the tv and try one by one to press 2 seconds only.
third. if you are okay with.. try to replace T-CON its small investments before you go to big one in case MBs i think the data clock at it cause this.. when panel disconnected this data rail will be open as no act from panel to it

others caps you mentioned... they are for tuner chassis

[Scoff]

Re: LG55UB850V no picture or audio - flashing LED's help please?

Well test that c235, test it in diode mode, then in ohm mode, tv unplugged, unplug everything from tcon then test it, then test it with just the panel unplugged, then test it with everything hooked up, still with tv unplugged from power.

Thanks for the suggestion. I have done this, and the readings on C235 are as follows:

Everything plugged into T-Con board = 8.81kOhms, diode mode = 2.430 stable
cn3 ribbon unplugged = 8.81kOhms, diode mode = 2.465 down to 2.250 and back up again and repeats - unstable
cn4 ribbon unplugged = 8.81kOhms, diode mode = 2.430 stable
lvds cable unplugged = 8.81kOhms 2.456 stable in diode mode
cn3 and cn4 unplugged = 8.81kOhms, 2.470 stable in diode mode
everything unplgged = 8.81kOhms, 2.465 stable diode mode