TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

[ngth82]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Good morning all -

I wanted to give you a quick update on the TV from yesterday night:

Setup
1. Both T-CON cables were connected in all cases.
2. Instead of masking off the pins, I reworked the T-CON itself. There are 0-Ohm resistors populated in series with each of the Vxxx pins.

I removed one resistor at a time. This guarantees the target Vxxx pin is "disabled" from the LCD perspective without worrying about the tape shifting. The resistor was reinstalled before going to the next one.

Rail name	RefDes,PAKSize,Value
VGL	R167, 0805, 0-Ohm
VGH	R165, 0603, 0-Ohm
HVAA	R177, 0805, 0-Ohm
VCM_CB/XB	R211, 0805, 0-Ohm

VCM_CB and VCM_XB are sourced from the same location (IC5 on the left side). IC8 is not populated on the board. R211 bridges VCM_CB to VCM_XB.

No change was observed on the display. The display was still black.

[budwich]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

I think you think that this is a science... :-)

I believe only a few have gotten to the "science" (ie. the exact design of the tv, flow of the signals and operation).

NOTE: I don't believe any have only "masked" one pin so doing this is unlikely to get much result. Not sure what else to suggest. Because you are not getting at least half of a screen consistently, that probably indicates a bigger issue at the tcon level and the signal exchange with the main board.

[ngth82]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Lol. I design and debug networking equipment for a living. Circuit debug is a science, but debugging a TV without schematics are just educated guesses

Okay. Good to know about one pin at a time. Maybe once I g eg through all of the other Vxxx, pins I can depopulate resistors first a “set” of pins if that’s possible.

I’m working on my son’s car today. It’s nice out. Something else to do for a bit.

[CapLeaker]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

I have to agree, you did put more than a fair share of work into this. Taking always only one resistor off won’t cut it, since you taped off like 15 pins before. Well, you got another tcon right? Maybe try the tape off method with that one?

[ngth82]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

I have to agree, you did put more than a fair share of work into this. Taking always only one resistor off won't cut it, since you taped off like 15 pins before. Well, you got another tcon right? Maybe try the tape off method with that one?

I reinstalled each component when i swapped over to the next voltage. All the resistors have been soldered back on so it's in the same circuit condition as before i removed any components.

Yes, i have a second identical T-CON. I can try the tape method when i get back to it... As far as i can tell, taping the right most 15 pins (too much) yields in two different results: a blank screen, or just a few vertical lines appearing. Power cycling changes that result. I think what i'm seeing is the same "random chance" that i got before in getting the screen just working "fine"

New approach: I'll start with the 16 right most pins along the right hand side of the right connector, I'll split it into quarters. With four groups, i'll try the 16 possible combinations of that.

1st	2nd	3rd	4th
no	no	no	no
no	no	no	yes
no	no	yes	no
no	no	yes	yes
no 	yes	no	no
			
etc..

[ngth82]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Thanks for keeping interest in this thread guys! I tried a few cases just a little bit ago on the "right" T-CON connector.

Pin 1 is on the far right side. Pin 80 is on the far left on that connector.

Here's the pin map that I was able to figure out so far. Some of the connector signals don't have a corresponding T-CON test point. I'll take a look at the right TAB PCB test points and ohm them out for the remaining pins.

Pin 	Signal  (T-CON RIGHT HAND CONNECTOR)
3	STV
4	CKV
5	OE
6	STVR
8	VDD_IO_33, VDD33
9	VDD_IO_33, VDD33
12	VGL
13	SQINV
14	VGH
15	VGH
17	VCM_XB, VCM_CB
19	TP1
21	POL
23	HVAA
28	RVAA, LVAA
30	GMxx
31	GMxx
32	GMxx
33	GMxx
34	GMxx
35	GMxx
36	GMxx
37	GMxx
38	GMxx
39	GMxx
40	GMxx
41	GMxx
42	GMxx
43	GMxx

And these are the cases that i tried. No behavioral change as of yet.

	PINS	PINS	PINS	PINS		
Case	16-13	12-09	08-05	04-01	Tried?	Comment
0	No 	No	No	No	X	No change
1	No 	No	No	Tape		
2	No 	No	Tape	No		
3	No 	No	Tape	Tape		
4	No 	Tape	No	No	X	No change
5	No 	Tape	No	Tape		
6	No 	Tape	Tape	No	X	No change
7	No 	Tape	Tape	Tape	X	No change
8	Tape	No	No	No	X	No change
9	Tape	No	No	Tape		
10	Tape	No	Tape	No		
11	Tape	No	Tape	Tape		
12	Tape	Tape	No	No	X	No change
13	Tape	Tape	No	Tape		
14	Tape	Tape	Tape	No	X	No change
15	Tape	Tape	Tape	Tape	X	No change

I have BOTH cables connected when i do this. Should the "Left" LVDS cable be disconnected?

[budwich]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

wow... yu are pretty thorough at things. Hopefully, some one with intimate tv knowledge of things will get curious and pipe in.

I would like you to back up just a bit.
Have you found a way to always get the set to initialize "properly" ( ie. see the appropriate status flashing at the end of some power up cycle).... so that it happens every time as opposed to random?

[ngth82]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Good morning -

I’m assuming when you say “initialize properly” that includes the screen working - if that’s the case, no, the screen operating correctly is at random. The turn on sequence and the observed status LED blinking has been the same “slow blink initlization” when the power button is pressed as discussed before.

[budwich]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

I am not referring to a display on the screen. I am referring to the status led and the start up of the set / main card itself. IF I understand you correctly, you ALWAYS get the slow sequence of blinks which is followed by the status light remaining solid there after.... right? Since you are not seeing a display AND status light remains lit, this appears to indicate that the main processor is not able to complete coms with the panel as the status light should go out if everything is happy.

Have you tried to do any firmware updates?

[ngth82]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Hi budwich -

Every time I press power - I get the slow blink, when the tv initialization completes, the status light is OFF. That this point - the screen still doesn’t work, but I can press the volume up/down buttons on the remote and hear it click.

Please refer to the behavior described in Post 29, item number 5

I haven’t tried the firmware update, but searching the TCL site, I didn’t see a file download either. I’ll search when I get back to my desktop.
https://support.tclusa.com/55s405productdownloads

[budwich]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

no problem... I just want to confirm as some times, things go "sideways" over the "internet of troubleshooting"... :-)

Again, the purpose is to establish that the main board is basically "functional" as some "steady state level". From there, as suggested, look for some firmware... failing that get a blank usb with an appropriate file structure and place a known file that the Ruku will take (sorry I don't own / never used one... and you can tell by my spelling). Once you are at "steady state", plug in the usb and again observe the status light along with hopefully a light on the stick.
Go from there.

[jostewcrew]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

just putting this out there....the tcon and the main board was replaced, this eliminates those including firmware. you have backlights and power so powerboard and led's are ruled out. this leaves the panel and its boards. troubleshoot these. fuses, components, then troubleshoot tabs. am i wrong? of course this is assuming the replacement boards are functioning, but for troubleshooting?

[ngth82]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

no problem... I just want to confirm as some times, things go "sideways" over the "internet of troubleshooting"... :-)

Again, the purpose is to establish that the main board is basically "functional" as some "steady state level". From there, as suggested, look for some firmware... failing that get a blank usb with an appropriate file structure and place a known file that the Ruku will take (sorry I don't own / never used one... and you can tell by my spelling). Once you are at "steady state", plug in the usb and again observe the status light along with hopefully a light on the stick.
Go from there.

Agreed. I do appreciate the double backing to confirm operational states. It's really much easier to see first hand than to "see" through words.

just putting this out there....the tcon and the main board was replaced, this eliminates those including firmware. you have backlights and power so powerboard and led's are ruled out. this leaves the panel and its boards. troubleshoot these. fuses, components, then troubleshoot tabs. am i wrong? of course this is assuming the replacement boards are functioning, but for troubleshooting?

Hey jostewcrew - you are correct. The main board and T-CON were both swapped... I think that really points towards the panel.

The "replacement" boards came from an exact TV model number that had a broken screen - someone smashed it, but otherwise i could see the menus come up on it. I've since sent that panel to the local eWaste drop off site. I kept the viable parts... and low and behold - came across this current subject TV. (That rarely happens).


Regarding the firmware update - i see a SPI flash that exists on the "right" side panel board between the first and second tabs. You can see this in the spreadsheet photos in post #43 when i detailed out the voltages and test points of each TAB pcb.

Anyone know if the firmware updates touch the SPI flash on the T-Con and the panel at all?

[budwich]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

BUT... the problem with where you are at is somewhere "down the line". I say this because, you replaced the cards "serially"... meaning one at a time. Thus, potentially, with the type of "comms" going on, one card may have set a state somewhere, then the other card was replaced which may have "learned" that state and so on.... such that I am not sure without some way of talking to the processors, you can determine if any or all are completely happy at this point. Of course, I am grasping at "imaginary straws" at this point hoping that one will break the camel's back so to speak and cause it to jump somewhere... :-)

To me a usb load of the main board would force the issue at completely resetting things IF the process works in some "normal" fashion.

[ngth82]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

As far as firmware updates go: i don't see it directly on the TCL website.

The tvupdate.roku.com site, however, offers what appears to be an update for their FW package... go to: https://tvupdate.roku.com/index?p=ve...CL&model=7105X

Step 1 - Brand - TCL; then type in model number 7105X. A dialog box confirms if the TV model is a 55S405... i chose "Confirm"

Step 2 - I downloaded the latest software. (an update.roku file)

Step 3 - This is where i get stuck. The website wants me to type in the 12-digit code that appears on the TV screen when i plug in the USB drive.

The labels on the main board don't offer help here as far as FW/SW versions go.

The screen doesn't want to cooperate so far today... i'll try continuing with the update the next time it displays video.

[budwich]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

good on you... I couldn't determine the 4 digit number plus letter to get that far.

Not sure what you mean about the web site want a 12 digit number... have you tried plugging in the usb?

Further, a while back I suggested you "finger some of the smd devices on the edge board during your testing ... especially in and around caps to see if they change anything... have tried any of that? your response at the time was you "fingered that tab" with no improvement. Another set / thread had a person cause imaging to show up with an "accidental touch" of some of the SMD's... hence the suggestion.

[ngth82]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

good on you... I couldn't determine the 4 digit number plus letter to get that far.

Not sure what you mean about the web site want a 12 digit number... have you tried plugging in the usb?

Further, a while back I suggested you "finger some of the smd devices on the edge board during your testing ... especially in and around caps to see if they change anything... have tried any of that? your response at the time was you "fingered that tab" with no improvement. Another set / thread had a person cause imaging to show up with an "accidental touch" of some of the SMD's... hence the suggestion.

Hey budwich -
Please see the screenshot from the Roku site. Not sure what they want from this. I tried plugging in the USB with the update.roku file the root directory.

When i plug in the USB, there is no behavioral difference for the status LED - nothing happens (the LED remains off).

Regarding touching the caps / using my fingers as extra capacitance - I've tried that and the result didn't do anything different. Thanks for the follow up.

[budwich]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

ahhh.... they appear to have a very interesting "protocol" to prevent loading of software either by choice or accidentally. I suspect the code causes a "launch exchange" between the roku (got the spelling right) module and the roku server system which maintains "compatibilities" among other things. So unlike other sets, it does even attempt to access and read the usb at the lowest level to see what's on it. Having said that, you did try the "firmware loading sequence" with your remote... right?

[ngth82]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Hi Budwich -

No, I did not try the firmware load sequence (e.g. manually going through the menus on the TV) since i'm "blind" without the display working. Per the instructions, it won't actually update until you get the 12 digit "check code" and the 6-digit "response" code

Per the manual, the 12 digit code appears to be an "interlock" of sorts. Page 122 of the manual (LINK):

• Step 4: When the download finishes, take the USB flash drive to the TV and plug it into the USB port. When you do, the TV validates the files on the flash drive and displays a 12-digit code.
  
• Step 5: Write down the code and the web address, and take this information back to your Internet-connected computer.
  
• Step 6: On the 12-digit code page, enter the code your TV displayed, and then click Next (This is what i call the "check code")
  
• Step 7: On the 6-digit code page, write down the 6-digit code that appears, and then take it back to your TV. (this is what i call the "response code")

"12- and 6-digit codes The USB update process uses a pair of codes to validate that you are authorized to install an update, and to ensure you are not attempting to install an old, unsupported version of the system software."

• Step 8: Using the TV remote control, select Next to move to the next screen, and then use the on-screen keyboard to enter the 6-digit code. When finished, select OK. The system update begins. Do not remove the USB flash drive until the TV restarts.

Holy moly, thats one way to keep people from messing up the update.. TCL/Roku's version of checks and balances. The firmware update experiment will have to wait until the display decides to work again. No luck at the moment.

[CapLeaker]

Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

I see you guys aren’t giving up yet! So I do have a suggestion:
Did you try freezing or heating any components on the little skinny board with the tab bonds?