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Old 03-31-2020, 04:48 PM   #41
ngth82
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Quote:
Originally Posted by budwich View Post
what.... sorry for get this post... I didn't see the pictures and missed the part about seeing a picture... wow.... forget this ->
not sure I understand the "power down" statement... oh, you mean cord disconnected in what ever state the set was in (ie. if operating, then it kind of keeps that state so that if you plug back in all you need is to do a "power button" start as opposed to wait for the thing to initialize... right?

anyway, it does appear that the main board kind of thinks things are hunky dory and appears to power up and down, in terms of state lights, OK.... so perhaps things from the tcon out are a target.

I think is you track down the vgl (which I will take as voltage gate low), that value should be more in line with -12v (guess). It is being loaded down or the driver has an issue.
Re "power down statement" -- From the "ON" state - i press the power button on the remote, the TV status does the fast "on-off-on-off-on-off-on-off" blink when receiving the IR command. The unit doesn't really turn "OFF" - all it does is turn off the backlights. I think this what i recall seeing on other working TCL sets. Turning it back on -- it's purely just a backlights needing to come on again, without the "initialization slow blink" sequence.

Yeah, it does appear that the main board thinks things are okay.

VGL is (-5.51V) on the T-CON.
VGL has a test point on the "left" tab board and measures (-5.51V)
VGL has a test point on the far "right" tab board and also measures (-5.5V ~)
Please refer to the voltage spreadsheet in post #19 for locations.

If this is supposed to sit around (-12V) - who is the consumer of VGL in a LCD??

With everything connected - VGL to GND is ~33kOhm. With the right cable disconnected, the right side measures ~41Kohm to GND on the right VGL test point.
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Old 03-31-2020, 04:50 PM   #42
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Quote:
Originally Posted by budwich View Post
IF you ever get back to the picture state again... leave it alone and check some of the voltages that you made note off way back... the ones dealing with VGL VGL VCM..
It's a waiting game and luck of the draw... i'll give it a go a few times and check voltages if it comes up again.
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Old 03-31-2020, 05:43 PM   #43
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

AH HA! It turned on again... i spent the last 20 minutes measuring an annotating voltages. Please see the spreadsheet in this post.

Please see Tabs 2, 3, & 4... it's the right most column with data .. marked "working 3/31" as the title.

Regarding VGL: With the TV working, VGL is STILL (-5.5V)

For the "right" board - fifth tab over, i measured HVAA as 0V when it was broken and 7.35V when it's working. The "working" voltage has been double checked... i wonder if this was a measurement mistake in the "broken" state..

VGH measured as 33.25V when the TV was in the broken state. It measures ~25V when it's working.
Attached Files
File Type: xlsx TCL 55S405TBBA Voltages_low_res.xlsx (651.7 KB, 10 views)

Last edited by ngth82; 03-31-2020 at 05:46 PM..
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Old 03-31-2020, 06:11 PM   #44
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Also -

While the TV is on, i probed the Mainboard differential pairs towards the connector to the T-CON. Diff pairs, 50mV/div and swept the time scale - no apparent signals? The amplitude would not be less than 50mV..

From the T-CON towards the cable connectors - i see signal pulses. Same with the diff pair test points on the tab boards. I'll look at them again when the TV finally "kicks the bucket" and turns off.

It's been about an hour so far - still running.


The very interesting data point here: I have the ORIGINAL T-CON and ORIGINAL Main board installed -- it was left this way after i went through all the combinations of "old" and "new" boards yesterday.
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Old 03-31-2020, 07:18 PM   #45
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Interesting... you are a good tester and with good eyes ... :-)
You are making some progress although I don't know where its going. My hobbyist level experience is long since been past.

I am almost thinking that the tape cutoff method might work.... although if you have a working screen, just leave the tv on forever... :-)

you got me overwhelm ... but a quick search provides at least this link. It will take a bit to digest things.
https://dipelectronicslab.com/panel-...ltage-explain/

Last edited by budwich; 03-31-2020 at 07:35 PM..
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Old 03-31-2020, 07:29 PM   #46
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Interesting indeed... but i don't know where this is leading either. lol

I ended up unplugging the TV a little bit ago.. Just wasn't working on it and i don't want a live SMPS plugged in unattended without the cover on.

I plugged it in just now. The TV does NOT work (not a big surprise). The LVDS on the tab boards show nothing now.

Maybe there is a "interconnection" between the TCON and the Main. Something is up... I may call it quits on this unit and just salvage it for parts --> at least the parts appear to be good with the high suspicion something is just wrong with the LCD.

Last edited by ngth82; 03-31-2020 at 07:32 PM..
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Old 03-31-2020, 08:59 PM   #47
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

This one is a helluva mystery, wonder if it's some goofy little component at fault??
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Old 03-31-2020, 09:44 PM   #48
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

It’s definitely somewhere between the t-con cables and the LCD or the LCD itself. I checked the caps already - no shorts, voltages seem to be good between “broken” and functional with a few exceptions as noted.
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Old 04-01-2020, 04:02 AM   #49
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

a "gross short" might not be the problem in terms of "always shorted" but maybe "collapsing" as it takes a load.

Do you have any idea of the sequence that gets a regular working image... eg. wait 20 minutes, power down, power up, hit menu, etc ?
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Old 04-01-2020, 09:34 AM   #50
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Quote:
Originally Posted by budwich View Post
a "gross short" might not be the problem in terms of "always shorted" but maybe "collapsing" as it takes a load.

Do you have any idea of the sequence that gets a regular working image... eg. wait 20 minutes, power down, power up, hit menu, etc ?

There is no sequence of events that gets the TV to a working state. I was surprised to get it to boot three times yesterday, but that is merely random as far as i can tell.

The first time it worked yesterday, it was about 30min-1 hour between the last time i had powered the unit up. About two hours later - i tried it again.

But before then, the TV had been power cycled numerous times before with no resulting image on the screen.

All i do is:
1) plug in the unit
2) wait for the status indicator LED to go from "full brightness" to "half brightness" (this seems to be when the TV is ready to accept commands.
3) hit power on the remote.
4) Watch the status LED slow blink;
5) Backlights come on
6) -- and at this point seldom see something on the screen.
7) proceed to whatever task i was out to do -- measure voltages.
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Old 04-01-2020, 10:41 AM   #51
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

:-( that's too bad but at least you know that a picture does come up and based on the one full screen shot (although limited), it appears to be OK.

You might want to try placing the tcon in the fridge, not the freezer, but regular fridge to bring the board done to a "nice cool level" and see if that changes anything. Depending, you could also try that with the main board.

There is still the "tape cutoff" method... can you determine where in the tcon to panel cable, some of the VXXX are... I assume near the ends of the outer connector.

Further, looking back at your posts, you indicated that you left it plugged and sitting for a while and then power it on to get a "lucky picture". Since, you indicate that 12v appears to always on (I would assume some sort standby driving voltage anyway), maybe a bit of heat is in order on strategic areas... main processors, power board components... ???? A hair dryer "shot" might help.

Last edited by budwich; 04-01-2020 at 10:46 AM..
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Old 04-01-2020, 11:40 AM   #52
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

That's one "cool" board! I can try that... i guess it won't hurt. I'd really like to save this unit if possible. Cutting tabs on the side is still my last resort once i deem the ROI on this is not worth it and we've exhausted everything else. (Although i'm pretty much there). I'll hold out some hope though!

Yeah, the screen does appear to be "OK" and looks great when it does turn on.

I tried the tape cut off method on the six far right most pins of the "right" T-CON connector yesterday night for a quick go at it. No change there.

I have a rework microscope in the garage so I can just cut the tape to the correct width and try some combinations of pins and record the data.

Looks like the Vxxx pins exist on the far left side of the left connector, and far right side of the right connector.... i should have some time around lunch time today.

Last edited by ngth82; 04-01-2020 at 11:41 AM..
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Old 04-01-2020, 09:09 PM   #53
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

I taped up both ribbon cables. I have a second set from the tv with the smashed screen


On the first try today, I taped up the “right” cable. All 15 pins from the right hand edge. I powered it on and this happened (see picture).

I powered it off and back on again - it went to black. If the tape method “fixed” it, I would expect the same picture result when powering on again. Wouldn’t you?

Tried several times again. No dice. No change. Picture remains black.

With that in mind, I taped the “left” cable and got the image to come up - first try. Power cycled, then it went back to black. (See second image)
Attached Images
File Type: jpg 2F275C21-8F74-488D-8819-83B5C82A1FA9.jpg (301.1 KB, 11 views)
File Type: jpg EE6F4953-9749-47CD-8024-3B987D93242F.jpg (313.4 KB, 12 views)

Last edited by ngth82; 04-01-2020 at 09:22 PM..
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Old 04-02-2020, 05:50 AM   #54
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

not sure of what you are saying... you got an image on a smashed screen?
also not sure what which cable you are referring with "right " and "left".
In addition, the tape cutoff method usually should be reproduceable in terms of image but that might be for a set with no side tabs... although with side tabs, I do believe people have not been successful or maybe they weren't persistent enough.
Still further, the method is very trial and error both in placement AND width... may read is the 15 pins is too much and also the "all 15 pins" on the edge isn't quite correct in location. I do believe there are some videos on the internet about this method.
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Old 04-02-2020, 06:43 AM   #55
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

i guess what he is saying is that the tape off trick on the TCon only worked once. When he power cycled the TV, the half picture went black again and remained black.

Weird.
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Old 04-03-2020, 08:52 AM   #56
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

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Originally Posted by CapLeaker View Post
i guess what he is saying is that the tape off trick on the TCon only worked once. When he power cycled the TV, the half picture went black again and remained black.

Weird.
Yes CapLeaker, that is correct.

I was working all day yesterday and didn’t have it in me to look at the tv. I’ll have more time after work today.

I know that taping over 15 pins isn’t the fix, likely it’ll just be a subset of pins. But if it “works” once, then it should be repeatable, right? It isn’t in my case.

Thanks!

Last edited by ngth82; 04-03-2020 at 08:56 AM..
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Old 04-03-2020, 09:15 AM   #57
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

What is your cable replacement / disconnect process exactly?
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Old 04-03-2020, 10:41 AM   #58
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

Hey Budwich -

1) Power off TV via remote then turn off the power strip
2) Discharge static to GND (typically just touch the exposed case screw my power strip)
3) Flip release mechanism on the TCON and tab PCB sides.
4) remove cable
5) Go to microscope, apply tape..
6) reinstall

Not sure what you are looking for specifically.
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Old 04-03-2020, 11:05 AM   #59
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

ok... thanks... I probably should have also asked what you are doing for the "repowering" attempt there after... which I assume is just a "power off / power on" from remote?
The difference between the sequence is likely "standby" versus "full startup". Not sure exactly what that would mean but with pins disconnected by tape, anything is possible.
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Old 04-03-2020, 11:07 AM   #60
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Default Re: TCL 55S405TBBA - backlights on, no video; T-con and main board replaced.

For power up - just hit the power button on the remote when the TV is ready (e.g. when the status LED goes from "full brightness" to "half brightness" as mentioned before). Push the remote power button and wait for it to come on. The TV does the usual slow pulsing of the status LED.
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