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Old 12-19-2018, 10:24 PM   #21
Amraks
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Default Re: Sasmung la40m81bd - Recapped

VDD = 3.24v
AVDD = 15.07v
AVDD_1 = 15.11v

Last edited by Amraks; 12-19-2018 at 10:45 PM..
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Old 12-19-2018, 11:29 PM   #22
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Default Re: Sasmung la40m81bd - Recapped

Just thought I would throw some more voltages up.
VCC_3.3 = 3.24v
VCC_1.8 = 1.85v
VCC_2.5 = 2.57V
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Old 12-20-2018, 02:53 AM   #23
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Default Re: Sasmung la40m81bd - Recapped

Looks good (unfortunately). Could be the main IC on the T-con itself is bad, since you do get some picture, so the main board is sending something, but it's not "rendered" properly. Other more experienced users are of course welcome to disagree, that's why we're discussing.
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Old 12-20-2018, 03:13 AM   #24
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Default Re: Sasmung la40m81bd - Recapped

I am wondering if it could be some of the caps I have used. as I did mix it up a bit with brands.
I have a ESR meter if you know what caps for the picture on the PSU I should be measuring let me know .
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Old 12-20-2018, 03:19 AM   #25
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Default Re: Sasmung la40m81bd - Recapped

Unless you used caps that you recovered from another board (used ones), you shouldn't worry about what brand they are, as it shouldn't matter. The brand only makes a difference in how long they last over time AFAIK.

Also, the power supply board is not directly involved with the picture: it supplies the voltages to the main board and T-con board which then do some stepping down of their own, so as long as the TV is turning on and displaying something, the PSU is likely not the culprit. Noise on the output of the PSU has to get pretty bad to affect anything, by which point the TV is likely not going to turn on at all, but your is, so there's a problem with an IC somewhere. A scope would be handy to analyse the power going into the T-con and main board and ensuring it's ripple-free.
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Old 12-20-2018, 03:25 AM   #26
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Default Re: Sasmung la40m81bd - Recapped

something I need to invest in is a scope.
if it is a IC I have a microscope to use for the fine soldering.
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Old 12-20-2018, 03:36 AM   #27
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Thumbs up Re: Sasmung la40m81bd - Recapped

Quote:
Originally Posted by Amraks View Post
something I need to invest in is a scope.
Ditto...
Quote:
Originally Posted by Amraks View Post
if it is a IC I have a microscope to use for the fine soldering.
Could be the main one (in the middle of the board) which is not replaceable from where I stand, because you can't find it easily, plus the price and labour would outweigh the cost of a replacement T-con. Good on you for having a microscope though...that's another thing I lack.
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Old 12-20-2018, 03:51 AM   #28
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Default Re: Sasmung la40m81bd - Recapped

Just measured pin 4 on TPS65160A in diode mode its reading 0.168v
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Old 12-20-2018, 03:56 AM   #29
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Default Re: Sasmung la40m81bd - Recapped

Would that reading be in relation to GND ? If so, repeat the measurement in ohms just for the sake of thoroughness. Still, pins 4 and 5 give you the boosted 15v output, which you seem to be getting, given you last results: AVDD = 15v. If there were any dead shorts, you probably wouldn't get any picture at all.
This is a good time to measure VGH (voltage gate high) and VGL (voltage gate low) as well since the pins are clearly labeled in the datasheet for the TPS. They are pins 10 and 11. From what I've seen, "ghosting" occurs if VGL is not functional (the screen is not "discharged" and the picture gets stuck). Conversely: if VGH is not "charging" the screen, well, quite predictably, you get no picture. These seldom fail though and from what I've encountered so far, if VGH/VGL are not up, the fault is not in the T-con, but in one of the buffer boards where there's a short that kills VGL/VGH and it's not repairable at that point (the short is most likely in the COF - chip on flex)

Last edited by Dannyx; 12-20-2018 at 04:03 AM..
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Old 12-20-2018, 04:28 AM   #30
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Default Re: Sasmung la40m81bd - Recapped

Never mind I wasn't even looking at the packages legs right lol

I measured pin 10 and pin 11
10 = 15.12v
11 = 4.54v
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Old 12-20-2018, 04:44 AM   #31
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Default Re: Sasmung la40m81bd - Recapped

Pin 11 should read negative (usually -5/-6v). Try and see if there's a pad labeled VGL connected to that pin (there's a diode in series with that pin, so don't measure AT the pin, measure after said diode). The example schematic in the TPS's datasheet illustrates this. See how there's a diode D2 on the VGL pin there ? Measure after it and see what you get. Should be negative. If not you could be getting closer to the issue now.
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Old 12-20-2018, 05:11 PM   #32
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Default Re: Sasmung la40m81bd - Recapped

So pin 11 goes to CD15 then to D4

D4: -7.79v

Added a picture of the voltages across that line.
Attached Images
File Type: jpg tcon pin 11 voltages.jpg (1.05 MB, 14 views)

Last edited by Amraks; 12-20-2018 at 06:04 PM.. Reason: Picture
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Old 12-20-2018, 11:17 PM   #33
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Default Re: Sasmung la40m81bd - Recapped

Would that value happen to appear at the test point marked V_OFF ? If so, it would seem they're not calling them VGH and VGL but rather V_ON (slightly higher, towards the mounting hole) and V_OFF, which is the same thing.

The value would seem right...a bit low, but should be within spec (the datasheet for the panel itself tells you exactly what it should be).

EDIT: also, could your describe, or better yet, post a picture of what the picture is doing currently ? I missed the video.
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Old 12-20-2018, 11:31 PM   #34
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Default Re: Sasmung la40m81bd - Recapped

Here is some more voltages I took.

VREFL_L = 330mV
VREFL_H = 6.45V
VREFU_L = 8.49V
VREFU_H = 14.68v

not sure if the top one is meant to have voltage going through it but it stands out as being something to pick on.
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Old 12-20-2018, 11:33 PM   #35
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Default Re: Sasmung la40m81bd - Recapped

heres a video i scrubbed the other one it had a kid screaming and I didn't think it was fair on you guys to listen to a baby screaming lol

https://youtu.be/d3zCpfB23Sg
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Old 12-20-2018, 11:36 PM   #36
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Default Re: Sasmung la40m81bd - Recapped

Wow that's bad...you could try heating up the main board like someone else suggested just to see what happens. Must admit I haven't seen anything quite like it, but that rainbow of colors could point to a faulty MB too...
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Old 12-20-2018, 11:38 PM   #37
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Default Re: Sasmung la40m81bd - Recapped

Quote:
Originally Posted by Dannyx View Post
Would that value happen to appear at the test point marked V_OFF ? If so, it would seem they're not calling them VGH and VGL but rather V_ON (slightly higher, towards the mounting hole) and V_OFF, which is the same thing.
That is correct must be a Samsung thing.
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Old 12-20-2018, 11:41 PM   #38
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Default Re: Sasmung la40m81bd - Recapped

Not necessarily. Actually this is the first T-con I've seen which calls them that. Samsung doesn't manufacture the boards anyway, so the original producer is free to mark them whatever they want if I'm not mistaken.

Could also be a bad LVDS cable, though I doubt anyone messed with it. Still worth trying to disconnect it, plug it back in at either end, jiggling it around, you know just to rule it out.
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Old 12-20-2018, 11:54 PM   #39
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Default Re: Sasmung la40m81bd - Recapped

Quote:
Originally Posted by Dannyx View Post
Could also be a bad LVDS cable, though I doubt anyone messed with it. Still worth trying to disconnect it, plug it back in at either end, jiggling it around, you know just to rule it out.

Have had this disconnected a few times after I got the tv back cables look good no ones been messing with them.
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Old 12-21-2018, 08:30 AM   #40
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Default Re: Sasmung la40m81bd - Recapped

Wonder if thats a match for your tcon? the first 9 numbers on the sticker match. https://www.ebay.ie/itm/TCON-BOARD-4...-/162987820813

Last edited by nomoresonys; 12-21-2018 at 09:04 AM..
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