Thomson 55UA7706 LCD TV startup problem?

[SMPS]

Hello.
My first post here.
I apologize for the typos because English is not my native and I haven't learned English in my school years. I have tried to learn it myself but probably I still make many of mistakes because reading written language and trying to communicate are two different things..OK, hope that these mistakes are forgiven

My concern is as follows:

I need help finding a service manual for Thomson 55UA7706 tv. Or - which may be the cause when the TV is in standby mode and the screen stays blank when you try to turn it on (even no backlight flash), I`ll connect new strips but I cant get 56V from BL inverter, there is two chips OZ9998HEGN in this inverter, they seems fine. Inverter board can get from the main power supply as follow voltages:

+24V (I have there +22.66V)
+56V (I have 0 (zero)V)
there is also
3D_EN pin (i think some logic pin?)
P_DIM (dimming I quess?)
PT (I dont know what it is?)
BL_ON I have there +3.06V (backlight ON? logic signal?)

Backlight driver module is: 40-RA6080-DRA2LG
Power supply board is: 81-PE461ED-PL200AA
Motherboard is: 40-NT67HC-MAD4HG
T-CON/ Logic is: ST4851D01-4-C-2
LCD panel is: LVU550SE4L 55E6700-LPE002A

Where else should I look or measure?
Thanks!

[Diah]

Re: Thomson 55UA7706 LCD TV startup problem?

first please upload photos over here on yours LED driver boards
use Flash light ( torch ) to see if the screen show any image at dark room...
in case yes you can see some things on the screen.. then while the TV ON. unplug the socket (24V) between power boards and led driver boards and plug it in again fast...see if yours back light flashing on or not.

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

Here it is.

This is inverter board.
I try this method but can you tell me - what is the purpose of this 24V node? 56V seems backlight power (72 LED in one strip, 4 groups 18 LED per group) but for what is this 24V purpose?

EDIT: No image if I illuminate the screen from different angles with a flashlight, I forgot this to mention in the first post.

[Diah]

Re: Thomson 55UA7706 LCD TV startup problem?

Here it is.

This is inverter board.
I try this method but can you tell me - what is the purpose of this 24V node? 56V seems backlight power (72 LED in one strip, 4 groups 18 LED per group) but for what is this 24V purpose?

EDIT: No image if I illuminate the screen from different angles with a flashlight, I forgot this to mention in the first post.

24V this the led voltage which it converted to high at led converter boards.

you wrote you have 3,3 on BL on.. so i assume the main boards working and send signal power on and bl on..
if there is no image on screen.. you need now to check if you have 12V on the T-CON .. it had fuse on it you need to check both side of the F1
if you have 12V

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

You mean this in red circle?

[Diah]

Re: Thomson 55UA7706 LCD TV startup problem?

You mean this in red circle?

yes this is the F1 fuse. put yours voltmeter black probe on chassis and the red one on each side of it and check do you have 12V.?

[budm]

Re: Thomson 55UA7706 LCD TV startup problem?

1) Show us the pictures of the whole backside of the TV so we can see how all the boards are connected together.

2) What Voltage do you get on P-DIM?

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

Sorry for delay.

Image from rear side, at below.

Quick measurement from T-CON fuse shows that this fuse is in good conditions (continuity test).
I haven't done this 24V circuit test yet but I will soon. How long can i turn on the tv without this 24V node? Can it damage the power supply if there is no load in this node longer time?
If I connect a relay between this 24V wire and turn on the relay (from aux power) a few seconds after turning on the TV, will it not damage the power supply itself?
Also, in a moment I can measure this P-DIM. When I get the result, I note here.



EDIT

Results are:

P_DIM +0.430V
Fuse F1 from T-CON, +11,988V (both sides)


Measured at inverter board IN DC MODE:
+56V pins: measured +41.45mV it is not very stable also - here seems something wrong ????????????
+24V pin: measured +22.92V (little low but not very?)
PT pin: measured +0.55mV
BL_ON: measured +3.109V (little low?)
P_DIM: measured +0.4316V
3D_EN: measured +0.62mV

[Diah]

Re: Thomson 55UA7706 LCD TV startup problem?

no need any relay ..
its save if you unplug the socket of 24V between PWB and LED converter boards.
so keep the socket unplugged.. and measure the 24V to see it come high to 24 or remain 22.92V.

by the way you should hear sound and can see picture on panel with torch ... if no sound or picture.. you can put back the socket of 24V in place.. and just disconnect the panel from T-CON ( just unplug the 2 ribbon cable from T-CON side) and turn on the TV ..check the back light come on or not

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

OK.
Haven't tried it yet but main PSU contains a FSFR1700XLS resonant converter switch https://cdn.badcaps-static.com/pdfs/...f141f56ce1.pdf

Found that there is one zener diode in this circuit part which is shorted, it is not exact circuit like Philco PH48S61DG (service manual page 14) but there may be some reference, this part of this main PSU produces LED driver +56V which I dont have. Hope that this FSFR1700XLS itself is good but I cant see any marking in this shorted zener (D 404 in picture) body, only blue band - what it is?

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

Nobody

I searched with different methods to maybe find some circuit diagram or fragment but nothing, in this PSU board is printed also: 40-E461CD-PWD1XG

But google says - no circuit diagram or even fragment this FSFR1700XSL part.
There is multiple PSUs which use same IC but all are little different - and I dont know what zener I can use to replace this D404 (measured, shorted) - there is also D402 and D403 and they are both 18V zeners (measured).

What happen if I connect this D404 place for example 9.1V zener or 12V (i dont have this 18V at this moment and local store does not sell SMDs).
Or can I just series connect two 9.1V one and just try? But if there must be some other (higher/lower) zener value, what is the result?
Most closest circuit I find is 40-E421C6-PWB1XG, there is weird note thereat D404: 79C18V (bzx79c18V?) but why - other zener is marked just 18V, why this exact D404 is marked like recomended model?

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

Want to EDIT last post but I cant

OK, last post here - no help and seems like there are not even like-minded people

Anyway, replaced this broken zener with 18V THT component but no change.
If before red standby light came on then now it stays off - broken zener=standby, new zener=no standby and no power.

I cant any information nor google, nor yandex, nor other search engine - why this zener is here? what they do here? What happen if they are too high or too low values or what happen if you leave it out at all? I cant get any information - from FSFR1700 datasheet there also not either even a little similar reference design...

There is not problem this 24V node, nevermind - this TV LED driver need 56V to feed LED stripe, there is 18 LED in one string, there is 4 strings in one stripe, one string need 56V to came on, no 24V , no, this 24V pcb track is maybe 0.5mm wide and there is no change that this current which 144 LED needs can get through this trace.
And this +24V is close enough +22,9V but - can't forget that there must be +56V, much higher current than this 24V and there is very little voltage at this +56V node, this is much biggewr problem I think...but OK, seems like there is no help anyway, some ask picture but no any words afterthat...hope that this "TV-inside picture collection" gives something interesting.

bye

[nomoresonys]

Re: Thomson 55UA7706 LCD TV startup problem?

Get the same zener and replace it, get a couple, maybe test the components around that zener to make sure they are ok before replacing, did you follow Diah's instructions? Don't give up, youtube is your friend, there is hardly a problem that many people haven't already encountered and solved, good luck, hope you save it.

[Diah]

Re: Thomson 55UA7706 LCD TV startup problem?

Want to EDIT last post but I cant

bye

MAN.. we are all willing to help you and any other posted issue over here..
but you are following your head ONLY..

yours power boards was working.. why you go to the HOT area and damage it.. did any one here write to check any component at HOT AREA ??

for me i hate to keep writing and suggest and OP just follow his head and brain. here we are... you are at lost.

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

no need any relay ..
its save if you unplug the socket of 24V between PWB and LED converter boards.
so keep the socket unplugged.. and measure the 24V to see it come high to 24 or remain 22.92V.

by the way you should hear sound and can see picture on panel with torch ... if no sound or picture.. you can put back the socket of 24V in place.. and just disconnect the panel from T-CON ( just unplug the 2 ribbon cable from T-CON side) and turn on the TV ..check the back light come on or not

---HOW it is possible if I disconnect socket where is also this low level signals? (where there was an explanation?) What picture I see then? If there is blank screen - do i need to connect something? No, there is NO any picture if I watch torchlight, I say it - i also feel like a buggy that i have to do things over and over again that i've already done it.
This cable is wery strongly in connectors - i can say that I haven't encountered ribbon cables so hard before and that's why I suspect they can't be caught in the socket (yes, I lifted the lock ... [because it's probably thought I haven't seen any electronic devices in my life]).
I can pull it open and see, what happen but whrere we are then? Same point because - no explanation. You ask whether F1 is OK, even you mention that there must be same readings at both sides - HERE i read like ...why i didn't read the suggestion that i can also do a continuity test...because I have done this tens of times (no tv but audio devices) and I would have mentioned at this if, for example, this fuse would be broken because it would have seemed bad taste right away..but it is OK - what next? (no explanation - OK, if this fuse is broken, T-CON is unrepairable, I quess? - no explanation, or...I cant see)

MAN.. we are all willing to help you and any other posted issue over here..
but you are following your head ONLY..

yours power boards was working.. why you go to the HOT area and damage it.. did any one here write to check any component at HOT AREA ??

for me i hate to keep writing and suggest and OP just follow his head and brain. here we are... you are at lost.

Yes, this board working also now (like they work before) - but also, what explains this zener D404 which is broken, if I replace this for 18V on standby doesnt come on, if i replace this for 2x3.6V items, also standby does not come on but if I place this broken (0.0009V zener reading and continuity test, shorted) zener place - woilaa - standby come on.
BUT this is pointless if there is not this 56V rail. Yea, I can pull these T-CON wires open but the inside feeling says that it does not change anything.

Can I get help from oscilloscope (I have this too), I have Fluke, newer UNI-T 5 digit meters and soldering stations, so-all this which i need to do audio things but I have no experiences this TV bullshitlike (just my thoughts) error prone power systems - I have lot of experiences raw-SMPS (some hundreds to 2-3kW O/P and to +-170V voltages at rails - there is all simple, huge input rectification stage, raw smps control circuit, H or F power stage, huge transformer, secondary rectification [for PA-AMP]), but i have no TV experiences - I ask only help, not bullying (that this stillness if I found this broken zener... if there is no any problem - who forbids to say it..nobody)

If we speak to hate or hating...I hate also many things, one is bullying

[Diah]

Re: Thomson 55UA7706 LCD TV startup problem?

if you are waiting on explanation on any test suggestion over here.. then we will wrote books..lol
take it easy..
most 3D TV set such Toshiba too HD or UHD, the Led back light will have an extra inverter boards and it work with feeding of 24V from power boards like yours.

unplug and plug in the 24V socket while the TV on. it will switch the inverter to be ON in case if its shutting off because of fault led at back light strips.

you said you cant see any picture on screen.. did you put signal... can you hear sound ?
this why we want to be sure the T-CON had 12V on F1.

remove one ribbon.. its test if the panel had fault or short so there are SOS signal go back to the main boards and it shut down the back light..

i don't know what are you talking about 56V... where should be? on LED strips socket?
if so then it will make no sense at all.. take out your screen apart and test you back light or by buy LED tester to be sure the back light all working.... still this make no sense again.. because you said there are no picture on screen with torch ..!!!!

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

OK.
Moment ago I did it - disconnect this black cable to inverter board and connect it back, there is no standby anymore after connecting back.
If I reconnect TV to mains there is only one very short blink in this standby - maybe because I try to replace this zeners today earlier.

Yes, there is no image and yes, i did not connect anything to input (HDMI or nothing) - maybe this is why not sound or nothing.

I have tester to test LEDs, they give me very weak light and I have also new stripes I connect this stripes and they dont give me any light if connected (they are new, also tested before and now too, they are OK (also now), gives me very bright light if connected to tester. Because I have DIY built tester I have 170V open circuit Voltage and if I test this stripe, one string (18 LEDs) gives me 87.7V. Sure that old stripes is broken because they are very weak, only darker room I see some light. And this 56V thing - some technician say that there must be this voltage - maybe they are wrong because they dont have also any service manual. But this 24V goes trought one wire and near the connector there is 2 series connected 47ohm 1206 resistors and this pcb track is also very thin compared to 56V traces and 3 wire. After this resistors 24V goes to 2SD1664 collector, this transistor is also low current - 144 LEDs to drive???

Maybe this original stripes is not broken and really there is some serious problem - I get this TV from friend, there is no money spent of that (only new LED stripe). Friend told me that if I want to tear it to parts then they give this TV to me. I was wondering if I could get it to work...this is not old, 2-3 years used.
OK, now I have more problems here and I think that if I find new PSU I can try this T-CON disconnecting.

If this fault now arise, there is no fire, no smoke, what went broken - there is now big question, maybe now this zener part...

In physical screen itself is good, there is no scratches or other physical marks. How often do panels itself fails electrically at all? If we take 1000 panels how many fail say second years when they are use? some orders of magnitude?

And yes, bad thing is that 3D model - people speak that this 3D is not very good, I have also one Philips 3D which fail after quarantee.
This Thomson is 55 inch, 4K (UHD).
I learn that Thomson and seems like TCL too is brands which I never buy - no manuals or nothing.
I have LG 42 FullHD and 6 years there is no any problems, before I have Samsung CRT...12 years or so - no any problems..
But seems like this good old days is ended and newer models is not that good like older.

OK, maybe some day I try if I find new psu or service manual.

-----------------------------------------------------------------------------------------------

But this zener mystery is haunting. I treated this psu before this measurements like any other high Voltage boards, there is no change that this zener fails if I disassemble this board, measured this broken zener after filter capacitors are empty (there is no resistor and 10-15 min to wait until they are not energyzed), if continuity gives me short, I soldered this zener out and measured Zener voltage - i get 0.0009V (measured at 25V test Voltage). This is mystery - why this broken component is in this board? This is really fist time when I see this kind of "planned obsolescense" thing..need to tear appart some newer PA amp, maybe I find this kind of "faults" more..

[budm]

Re: Thomson 55UA7706 LCD TV startup problem?

1) Show us where the '56V' pin you are talking about.

2) Can I get good clear straight shots pictures of the whole top and bottom side of the power supply board? Right now your pictures are not clear enough for me to clearly read any prints on the board.

[SMPS]

Re: Thomson 55UA7706 LCD TV startup problem?

I think that this maybe is also not good but I have night and my phone cam is not good to make better pictures.

And if I want take a picture to whole pcb, i cant take it very close
There is limit also if I take many shots closer and put them together.



And LED is this: https://www.aliexpress.com/i/33023939915.html

If I search from google all this PCBs (all markings which there is) then I only get different e-store etc, no topics, no information which I need. Some chinese page but maybe tomorrow I try chinese pages.
At this moment there is probably not much to do - I dont know what is this D404 zener value - if I order new FSFR1700 chip I dont know anyway which zener there MUST be - I am 99.9% sure that this is not broken if this TV shipped out to factory, but maybe because I try different zeners today its also my fault now and maybe this IC is also broken because I connect one times more TV to mains and there is now only short standby flash.
Maybe now is really time to throw it away or only new PSU because (this service manual searching led me trought multiple manuals) all TV PSUs nowaday seems very bullshit - tens of different "failsafe" circuits which fail first itself... for why?
At this moment I dont really know anymore - maybe this fault is now gone further now because there is not a way to sort it out - sure that I have very little change to get this model PCBs at my country..
Need to order and even then there is 50/50 change. This psu IC also - I can order it but if there is "failsafe" which lets smoke out this IC to protect this "failsafe" circuitry - what is the point to order and solder. I dont really understand - broken zeners, weird voltages...I have to repair some time ago much valuable PA amps and there is no this kind of "failsafe" things, I was made this year some IR2153, IR2161, IR2156 based smps to my DIYbuilt amplifiers and there is not this kind of "failsafe" there is no problem also if user know what they do...TVs and their "systems"...i dont have a words more

[budm]

Re: Thomson 55UA7706 LCD TV startup problem?

1) The pictures of the boards are very poor, I cannot read the pin label (the oin names are printed on the bottom side of the board) of the connector of the power supply board that goes to the LED driver board.

2) Were you getting 24V to the LED driver board? And now you don't since you start playing with FSFR1700XSL and D404?

3) The 24VDC is generated by FSFR1700XSL so the circuit was working. I do not understand why you start messing with the FSFR1700XSL.

4) As you can see that D404 is connected in parallel with resistor. So when you check D404 off the board, does it show conduction and low resistance (<10 Ohms) in both directions.

5) Right now you need to get the FSFR1700XSL working again before going back to troubleshooting the backlights issue, or just buy a new power supply board assembly that match the number on the barcode sticker, not the blank PCB part number..

6) Where is the pin that is supposed to have 56V?