SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

[diif]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Driver/panel whatever they are called. Why would 12v be going to them, there doesn't seem anything to drive.

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

What's the 8 legged IC on the driver board ? a winbond eeprom ?

there are 3 of these 8 legged IC's but i think the one you're talking about is the bigger one close to the panel ribbon connector (input from mainboard) which is a winbond chip.

what does this mean for me?? i have a lot to learn!

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Driver/panel whatever they are called. Why would 12v be going to them, there doesn't seem anything to drive.

doesn't the panel need some voltage to work? doesnt the TCON usually send 12v to the panel boards and a bunch of smaller signal voltages? or is it only the small signal voltages?

[diif]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Looking closer there are some test points, the voltage conversion is usually done on the tcon but this is done on the mainboard.

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Looking closer there are some test points, the voltage conversion is usually done on the tcon but this is done on the mainboard.

which test points do you mean?
and yes the TCON is integrated into this mainboard. but i dont fully understand the nature of the relationship between TCON and panel boards so im a bit lost.
I figured since im seeing 0V coming out of that IC which feeds some pretty major coils that that must be the problem...
and that i see no voltages going to the panel cable...

also i should mention if i havent already that disconnecting the shorter panel board from the longer one results in the TV turning on in a stable way and backlights staying on everything but still no picture.

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

according to what im reading, shouldnt i expect to see VGH of maybe even 15v?
https://pcbartists.com/design/power-...matic-tft-lcd/
regardless. no voltages at any of the pins of the panel connector leaving the mainboard is definitely a sign we wont get any picture...and seems like a mainboard error, doesnt it?

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

ok i dont know how i failed to measure correctly but there IS voltage at the panel connector leaving the mainboard. a bunch of pins have small voltages like .4 or .25 on them and a few have 1.something and maybe even a few 3.5...
and there are very many tiny test points on the panel boards. it will take me some time to measure those and post pictures. sad part is though, the equivalent of VGH and VGL are on the smaller of the 2 boards which when connected, causes the TV to go into boot loop, so...hard to measure. maybe i will see them for a second before reboot. getting somewhere maybe? still concerned over many parts of the MB at 0V tho.

heres some voltages on some of the other coils that arent 0.
and i tested quickly some of the panel driver boards test points and i found that there was .4 and 1.something voltages at a lot of places. 0 voltages on quite a few, and notable 0v on the two that are at the far right end of the connector coming into the panel boards. those would be the higher voltage pins i think because on the mainboard side there are a few larger mlcc caps right there. which of course read 0v.

a major reason i thought no voltage was getting to the panel boards is because all the mlccs i tested on there read 0.

i gotta run for now. but ill be back at it ASAP.
thanks to anyone who tries to help!

[diif]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Have you written the other voltage on the power supply?

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Here are panel board pics with voltages

first set of measurements are done with only the first panel board connected. many voltages are completely missing.
SxxP, SxxN: all of these measured .42 and .43
TEST_OUTX-COFXX test points 0,1,2: the first 2 or 3 COF's are at 0.38v, 0.01v, 1.85v
but there was a split somewhere and all the others from that point read 0.37v, 0.01v, 1.78v
... not sure what it means but its noticibly different.
VCOM=0
VH0=0.1v
VH255=0v
VL0=0v
VL255=0v
clock lines CK1-8 all read 0.1v
CLR=0.1v
STV=0.1v
VSS=0.1v
VGH=0.1v
LC1=0.1v
LC2=0.1v
SFC = 1.8V
TEST_EN1 = 0
TEST_MODE1 = 0
SRF=1.8V
XON=3.11V

second set of measurements are done with the second board connected.
voltages are the same on first and second boards in this situation.
with the second board connected,
the TV constantly reboots. backlight comes up, changes brightness, turns off, tv turns off, reboots, etc
during this time, voltages can be seen to come up and then cut out.
all voltages listed are the max they get up to before cutting out.
some of the voltages are there for longer of the time than others.
the higher voltages are only there for an instant before cutting out.
the lower voltages are there most of the time and only disappear during the cut out.
all voltages cut out at some point during the reboot.


SxxP, SxxN: all of these measured .42 and .43
cof test points 0,1,2: these seem to read a little higher than before, cutting off at 0.4v, 0.01v, 1.85v

VCOM=7v~
VH0=8v~
VH255=15v~
VL0=7v~
VL255=0.35v~
clock lines CK1-8 all read -6v~
CLR=-6v~
STV=-6v~
VSS=-6v~
VGH=25v~
LC1=25v~
LC2=swings between -6v and +7v
SFC = 1.8V~
TEST_EN1 = 0.2v~
TEST_MODE1 = 0.2v~
SRF=1.8V~
XON=3.11V~

so as we can see, with the second board disconnected,
the higher voltage doesnt even try to come up. not on the mainboard or the panel board.
with the second board connected however, the higher voltage tries to start up, gets as high as 25 on VGH, and then cuts out, rebooting the TV.
i havent looked at voltages on the mainboard yet in this looping situation, but i did check those two larger MLCC's by the panel board ribbon cable and they do show the 25v VGH that cuts out.
i dont know enough to say for sure but it seems like by the design of the TV, if you dont have both panel boards connected you dont get any high voltage, so would see nothing on the screen.
this makes it hard to tell which board has the problem. if each board could independently drive its own half of the screen, we'd be a lot better off. older TV's did this. newer TV's are coming up with tricks to keep us from fixing!

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

measuring the gate pin of IC1603B_UT while the power is cycling, i notice some funny behavior.
the pin starts out at 0 of course when the tv is in the off part of the cycle.
as soon as the tv tries to power up, the voltage jumps up to around 9v, but then very quickly drops down to around 6v, and then very quickly shoots back up to 12.8v and stays there for the rest of the cycle until the tv turns off again. i watched it for a few rotations and kept seeing my meter doing this.
an analog meter would give a better idea...or a scope....but i have neither!

[diif]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

The ICs, what are they on the driver boards ? Not the Winbond.

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

Have you written the other voltage on the power supply?

theres not much to tell about the power supply voltages. they are all there.
testing without plugged into mainboard:
there are only 13v power rails which are all there at 12.9v
there is analog dimmer (ANADIM) which when i measure it, the backlight dims a little and voltmeter reads 0.05v
there is power on/off which is at 4v
there is back light on/off (BLU_PWM) which is at 3.3v

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

The ICs, what are they on the driver boards ? Not the Winbond.

i believe it says AAT7212
RJLFP0

and yes there are 2 of them. and they are same.

[diif]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

theres not much to tell about the power supply voltages. they are all there.
testing without plugged into mainboard:
there are only 13v power rails which are all there at 12.9v
there is analog dimmer (ANADIM) which when i measure it, the backlight dims a little and voltmeter reads 0.05v
there is power on/off which is at 4v
there is back light on/off (BLU_PWM) which is at 3.3v

There were two test points next to the connector, you have given one, I don't think you have given the other.

I suspect the fault is in the panel or on one of the driver boards.

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

There were two test points next to the connector, you have given one, I don't think you have given the other.

I suspect the fault is in the panel or on one of the driver boards.

Yes as it behaves the same way even with the replacement main board we really have to lean toward panel or driver boards. There is always some chance that the main board they sent is defective in the same way. There were no pictures to prove otherwise.

I don't understand why you are concerned about the power supply though. It seems to check out 100%
Am I missing something here?

And those 2 test points near the psu to mb connector on the psu side? One of them is ground...so 0v

Obviously I am hoping the fault is in the main board or the panel driver boards and not in the panel itself, but more than that it is important for me to learn how to tell for sure which of the three it is!

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

I went back and put the tape on the panel cable to block those pins again and see what voltages look like then with a stable TV not turning on and off, both panel boards connected, still no picture. Turns out the pins I blocked are pin 15 and 16 from the left in my picture...which correspond to CLK3 and CLK5 ...the result is a stable TV with a blank black backlit screen but never any generation of the higher voltages (25v, 15v, 7v. 8v) that we see spike up and fall away when we leave those pins unblocked. How does blocking those two clock pins cause that voltage not to be generated?

[diif]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

They are test points that indicate where the fault it. 0v tells us it's the panel.
The panel to LG is the replaceable part so it's on the driver board or panel.

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

They are test points that indicate where the fault it. 0v tells us it's the panel.
The panel to LG is the replaceable part so it's on the driver board or panel.

sorry i dont understand. what exactly are you saying here? do we have enough information to tell which part has the problem?
are there more measurements i could take? i seem to have hit a wall with no way to tell for sure if the problem is from the mainboard, the panel board, or the panel itself.

what do you mean by "The panel to LG is the replaceable part?"

and what do you mean by "0v tells us its the panel" ? which 0v tells us this?

[diif]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

The two voltages I asked for a diagnostic points. The 0V indicates a panel fault and that is the part LG would replace.
As the driver boards are attached to the panel they are classed as the same thing to LG. You can't replace one without the other.
If you can find a shorted capacitor on the driver board you are in luck, it's possible it's one buffer ICs, if not it's the panel.

[triplefour]

Re: SAMSUNG UN50TU8000F rebooting, backlight ok. No 12v to panel boards.

The two voltages I asked for a diagnostic points. The 0V indicates a panel fault and that is the part LG would replace.
As the driver boards are attached to the panel they are classed as the same thing to LG. You can't replace one without the other.
If you can find a shorted capacitor on the driver board you are in luck, it's possible it's one buffer ICs, if not it's the panel.

this is a samsung tv not an LG and those two test points you asked for are on the power supply! how could that have anything to do with the panel?
one of them is 0v because its is ground. am i missing something here?

and the tv is out of warranty so SAMSUNG wont be replacing anything.