Samsung UN55MU8000 - Backlight But No Picture Problem

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

So now i will tell you something important.. as another (maybe the hundredth) time, this seem to be a proof of that panels (matrix controls, tcon and backlight) are destroyed by tension spikes, that can cause multiple damages, so your backlight is bad toghether with the fault at matrix electronics, sadly, so its a challenge repair both.. I dont suggest you starting with the less important / easier backlight, before you find the obscure one.. dont you agree? I will let you know that finding the panel's firmware will be almost impossible unless the magic Lotas comes in help.. have you got an hot air station? Truely it can be easier or safer to remove the diodes with stylus with a big blob of solder because them are tiny.. dont use flux that makes harder to join the sides with the blob.. 7 seconds job! And the tooth is removed..

Thank you again @Davi.p.
So you have convinced me that this is primarily a panel issue...possible multiple issues within the panel. And the chances of resurrecting it is slim. I can now temper my expectations. But this is not a total waste as I can use this opportunity to learn about panel repair which was one of the main goals of doing this repair.

So you say one of the issues would be with the WINBOND 25Q32JVIG chip pictured here? Its the only SPI chip on the panel board. When I tested it it was not shorted and it had 3.3v going to it.

To fix this problem I would have to remove it and rewrite the firmware to it.

[This is something that I have absolutely no experience with but I have am sure I could learn it easily.]

Another option would be to find the SQI from a donor TV or LCD Panel board with the same part number.

The part number of this panel is 16y_10vu55sl4lv0.0 left.
Would this work assuming that the donor TV was actually working?

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

Are you sure about panel model? Is there no sticker on the chassis? If panel is the same must work but can be another issue

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

Are you sure about panel model? Is there no sticker on the chassis? If panel is the same must work but can be another issue

The actual Samsung part number of the LCD Board Panel is BN96-41982A but is a secondary part number printed on the board.

The panel itself (which I think is what you were actually asking about is CY-SM055FLLV6H.

I have ordered a CH314A USB programmer as well as a few WSON interface boards for this job. I will ask @lotas if he has the file for this panel. If not, I will order the LCD panel board and read it off of that.

Happy to learn something new!

Thank you much!

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

I was able to pull the firmware off of the panel board's chip and posted it to the eeprom dump thread. I had to pull it off and read it via an WSON-8 adapter and a CH314A programmer. Im hoping to hear back soon on what's what. Pretty excited to get here. I've never done this aspect of TV repair before. Also excited to see what new adventures this CH314A Programmer will lead to.

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

Well i hesrd from @lotas and he tells me that the chip that i pulled off the LCD panel board woudlnt have anything on it that would prevent the panel from displaying a picture. If i understand it correctly thst chip is used to store calibration/corrections wheb its manufacturered.

He did point me to a proably suspect which would be any other 25-bios chip on tbe mainboard. It would be the one that stores the t-con firmware. And THAT would certsinly give us a no picture problem on the display. Im learning a lot with this particular repair. When inget home tonight i will try to identify this T-Con chip and see if i can get a dump off of it.

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

Which tension do you have on these points?
for the spi eprom you have to measure each one of the 2 spi eproms on the vcc pin in standby, the one related to tcon is the one not fed.

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

Which tension do you have on these points?
for the spi eprom you have to measure each one of the 2 spi eproms on the vcc pin in standby, the one related to tcon is the one not fed.

If by 'tension' you mean voltage then I have only seen voltages of 3.3v in a few places and ~1.8v in others on the LCD Panel board. I have not measured the voltage at that connector (on the mainboard) only at certain points on the panel board. I can test them if you think the LVDS cable maybe an issue.

Thank you for pointing out how to ID the t-con BIOS chip. I will power the TV see if I can get it to go into standby mode. The bios chip maybe under the heatsink as I dont immediately see them in the picture.

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

maybe those voltages are not important, but there possibly is a mosfet on the mb that switches the voltage for the panel at a certain point of the initialize, must be check.. it probably switches 12v

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

maybe those voltages are not important, but there possibly is a mosfet on the mb that switches the voltage for the panel at a certain point of the initialize, must be check.. it probably switches 12v

I believe you.
Ive gone through and tested all the voltages at the common test points. I still haven't discovered why AVDD, HAVDD and VGH are all 0 volts. Must be a mosfet but I haven't found any that are shorted. I haven't identified which mosfet(s) are responsible for sending these voltages either.

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

this could be one of two causes , the mosfet switching the 12v is not functional, but rather difficult, the pmic is turning down dc dc converters due to short on panel, i vote for this

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

this could be one of two causes , the mosfet switching the 12v is not functional, but rather difficult, the pmic is turning down dc dc converters due to short on panel, i vote for this

But wouldn't I see voltage if LVDS cables to the panel were disconnected? Since the PMIC no longer detects a short (bcos nothing is connected).

[lotas]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

To run T-Con without a panel, you need to put a jumper on the motherboard (imitation of the panel).

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

search if a test point named tcon ok is present and tie it to 3v

[lotas]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

search if a test point named tcon ok is present and tie it to 3v

No, you need to connect the points FB_TRDY_1 and FB_TRDY_3.

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

good

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

Fantastic tech support @davi.p amd @lotas!
I will go in and jumper these 2 points tonight and report the results!

Invaluable knoweldge and insight. I really appreciate it.

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

So I went in and added 3.3v to FB_TRDY_1.
I used the Panel Testpoint which has 3.3v and verified that it was getting to the correct pin.

After powering up the set and using the remote control to get to the main menu (via sound prompts) I tested AVDD_17V, HAVDD_8.5V, VGH and STVP1.

They all read 0V.

Just want to confirm that doing just FB_TRDY_1 is correct. I think this would simulate having just 1 LVDS cable connected which should still work as we often test these TVs with either panel cables connected.

[lotas]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

Who told you that the node should apply 3.3v to the FB_TRDY_1 point?

https://www.badcaps.net/forum/showpo...3&postcount=74

[Davi.p]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

sorry i have read so but never tested, anyway no problem, no damage, sure enough...

[KYBOSH]

Re: Samsung UN55MU8000 - Backlight But No Picture Problem

Who told you that the node should apply 3.3v to the FB_TRDY_1 point?

https://www.badcaps.net/forum/showpo...3&postcount=74

My apologies! The way i read the conversation between you and Davi.p was he mentioned injecting 3.3v to the T-CON test point but you came in and said it needed to be injected to FB-TRDY 1 & 3. So i take that there is no need to supply voltages anywhere for this particular test.

So when i get home i will connect FB-TRDY 1 & 3 together and check the test points again.

Thank you for the clarification!