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

[Scoff]

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

Thanks for the link. There are a few similar transistors, however I do not know which values are ok to be different to the values of the 2sc3052? I would guess its OK to use an alternative transistor with a higher operating temperature rating, however for things like Ft, Hfe, Vce etc do those values need to be the same or higher, or the sane or lower than my 2sc3052?

[nomoresonys]

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

https://alltransistors.com/crsearch....e=120&caps=SP0

[Scoff]

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

I'll see if I can find a UK supplier but so far all I have found are suppliers in China and that means having to wait a month for the boat to get here! Perhaps there is an equivalent to the 2SC3052 transistor that is easier to find....

[nomoresonys]

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

That makes sense to me, I think I would switch it out for a new one.

[Scoff]

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

Just to clarify - the above readings that I took were taken with the MB removed from the tv, and no cables plugged in at all.

As far as I can see both transistors are identical and have part number 2SC3052 and have LF scribed on top.

I would have expected both to give the same readings, or at least follow the same structure - reading with probes one way, infinite reading with probes the other way around.

If readings were affected by measuring while the transistors are in circuit, I would have expected at least the same pattern of readings from both transistors.

I have tried heating the area under the DDR and processor as suggested by Diah in post #87, and once cooled down and asking tape removed, I refitted the board. Sadly it still exhibits exactly the same behaviour as previously. At least I didn't make it any worse. So perhaps not a bad solder joint on DDR or processor - perhaps faulty DDR or processor instead? Unless the transistor Q2301 in indeed faulty and could be causing these symptoms?

[nomoresonys]

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

If they are both npn transistors then something is wrong.

[Scoff]

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

One other finding I meant to report, was in response to your picture highlighting the Q2301 NPN Transistor 2SC3052 in your post #73.
These are the readings I have taken with my DMM in diode mode:

- probe Base, + probe Collector = 2.914
+ probe Base, - probe Collector = 0.716

- probe Base, + probe Emitter = 2.578
+ probe Base, - probe Emitter = 0.719

- probe Collector, + probe Emitter = 1.577
+ probe Collector, - probe Emitter = 2.682

As I am new to these type of device I read up about them. If I understand correctly, the transistor is effectively 2 diodes. Therefore readings should only work with the probes one way around, and you should read infinity with the probes the other way around? If that is correct, then there is something wrong with this transistor?

For reference I carried out the same checks on another transistor, Q2303, which is also a 2SC3052,

- probe Base, + probe Collector = 0L
+ probe Base, - probe Collector = 0.707

- probe Base, + probe Emitter = 1.805
+ probe Base, - probe Emitter = 0L

- probe Collector, + probe Emitter = 1.804
+ probe Collector, - probe Emitter = 0L

Does this confirm a faulty transistor Q2301?

[Scoff]

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

Yes it was the heat gun I used previously, not the dremel flame one lol although the dremel is good for gas level control to control the amount of heat in a small area.

I did laugh when I read your "belong to yours fantasy" comment - I think I understand the translation - hopefully you mean "use your imagination"

I'll get things masked up on the board to protect them and find a way of propping the board up allowing access for the heat gun underneath. I have a 0.5kg weight I can use on top of the heatsink too. I'll report back once I've let it cool down and reinstalled it.......

[Diah]

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

i do suspect ONE DDR make this issue.. also

i do hope you didn't used the flame heat before..LOL .. so use the big one.
put yours MB as the up side to the top on 4 legs stand. ( belong to yours fantasy ), put load round 1/2 Kg on the main IC sink to preform pressure down of the chips and DDR.

after you masking tight all caps in RED. you stand the heat gun under the Boards ( yellow areas ) to start heating leave it cool then install.

[Scoff]

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

Here is a picture of the entire back of the board - let me know if you need a close up picture of any parts in particular



I have 2 heat guns - one large generic 2000W with 2 settings, and my gas powered Dremel soldering iron which has a much smaller hot air tip

[Diah]

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

take out yours MB from the TV and upload clear photo of the boards back side. there are way to handle this.
also show me yours heat gun you used before-

[Scoff]

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

After performing a factory reset from the tv menu, I have noted the following.
At first boot up, and every subsequent power on, the following sequence takes place:
1) tv in standby. No buzzing. Nothing on the screen. Press power button on RC or tv, red status LED at front of screen flashes for the first time. LD2300 on MB is now lit up solid red.
2)After approx. 0.5 seconds LD1900 on MB lights up red for approx. 0.5 seconds and goes off again. Red status LED at front of screen flashes a second time. After approx 0.5 seconds LD1900 lights up red again and stays lit up this time. After another 0.5 seconds the backlights turn on.
3)LG Logo splash screen appears on the TV correctly. After another 0.5 seconds the buzzing starts and 2 second cycle of buzzing and screen issue has begun. LG logo then disappears but is affected by the screen lines and brightness issue before it disappears.
3) Red status LED at front of screen flashes third and final time.
tv is now fully on.

I can step through the initial setup screens fine, all menus' and setup steps complete ok. I can navigate all tv menu's no problem. The screen looks perfect every 2 seconds.

During shutdown, the following happens:
1) tv on, no Red status LED at front. Press power button on RC or hold in joystick button on tv for 2 seconds.
2) Screen and backlights immediately turn off, and approx 0.25 seconds later LD1900 goes off.
3) LD2300 stays on for approx. 1 second and there is one final buzzing - then LD2300 goes out and buzzing stops immediately as soon as LD2300 goes out.
4) Standby red status LED on front now comes on.

My current firmware is the latest available for this model, 05.05.90, so there is not an updated version that I can try to install via either network or USB. LG do not let you install an older version of firmware, as it checks if a newer version exists already before allowing an 'update' to take place over network or USB.

The Main Board numbers are EAX6568460411.0 and EBT63083604

[vinceroger69]

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

what main board number is used in your tv it shoult start with EBT i think, (number maybe on a sticker etc )

[Diah]

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

if you do reset from the menu setting at which state after restart the buzzer will start.... same way if you send instop... we may find the start steps which cause this buzzer during boot

[Scoff]

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

I think the problem we have is with the angle of the camera in some of the photos. It can make things look different to how they look to the naked eye.

Regarding the coil filter 2R2, again the camera photo might look like it has some sort of heat damage, but it looks completely normal to the naked eye, and identical looking to the other 2R2 coil filters on the board. My meter doesn't test inductance, however all 3 of the 2R2 coil filters read 1.5ohms when on the resistance setting.

I have checked the micro switches and they are not stuck down. When pressing or pressing an holding for 2 seconds, they briefly stop the buzzing and the LD goes out, then the LD comes back on and after a second or so the 2 second buzzing cycle begins again.

I see there are quite a number of T-Con boards for sale second hand which have the correct part number for my tv, so I think for the relatively small outlay it may be worth buying one and swapping it out to see what if any difference it makes. If no different then I can hopefully sell it on again!

There still aren't any second hand main boards for sale anywhere that I can find - lots of hits on google search but they all show 'out of stock' of used second hand boards.

[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

[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

[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.

[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.

[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