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

[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

[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.

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!

[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!

[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.

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!

[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.

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.

[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.

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?

[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!

[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.

The other voltage? The lack of coils on the driver boards suggests there won't be 12v on there.

im having trouble following you. what do you mean by driver boards? the panel boards? yes there are no coils i can see on them. those are on the mainboard and they are not producing 12v. most likely because they are not receiving it from the other side of that IC ive pointed out. which is at 0v and most likely the output of the IC is at 0v because the gate pin is at 12.8v when according to the datasheet it should be at 1.7v or something. im trying to figure out why im getting 12.8v at that gate pin.
aside from any of that though, back to basics:
shouldnt 12v be going to the "panel driver boards" on one or more of those pins on the panel connector?

[diif]

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

The other voltage? The lack of coils on the driver boards suggests there won't be 12v on there.

[triplefour]

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

Remove the cable between the power supply and mainboard, do the back lights come one and stay on ?
If yes, what are the two voltages on the test points next to the backlight connector ?

backlight stays on with mb disconnected.
12.9v at those test points

[triplefour]

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

heres some voltages. does the 12.8 come from the 12.9 thats on pins 1-3 going thru that mlcc, and ending up at pin 4? the 12.8 disapears right there on the other side of what measures in circuit as a 30 ohm resistor just to the right of the tiny cap. i say disappear meaning it doesn't go to ground right there. if it went to ground then it would say 0v. its 12.8v there and i cant figure out if thats where the 12.8 comes from or thats where it goes, somewhere? via a via?
the mlcc in question (the tiny one on the left that has 12.9 on the bottom side and 12.8 on the top side)
does not measure short or low resistance. it measures quite high. well just shows a high resistance for a second before it goes infinite...which is what i expect a cap to look like.

[diif]

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

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

[triplefour]

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

i dont believe i have a backlight problem. the backlights come on and stay on just fine if i remove the panel connector. also sound can be heard from the tv, and the mainboard functions fine for on/off
i am not getting 12v out of the IC1603B_UT which i am trying hard to trace at the moment. will upload a picture with measurements soon.
ill check those voltages u mentioned as well. thanks.

[diif]

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

Remove the cable between the power supply and mainboard, do the back lights come one and stay on ?
If yes, what are the two voltages on the test points next to the backlight connector ?

[triplefour]

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

well its officially a nightmare TV. Client ordered the replacement Mainboard and it is behaving exactly the same way. no 12v coming out of it to the panel. But since i was hasty and not paranoid enough, i installed the replacement mainboard before making any resistance checks, and installed the panel cable before making any voltage checks. so who knows. maybe it DID produce 12v but something on the panel fried the new Mainboard? is that even possible?
or is it possible the guy on ebay sent a part with the exact same problem even though he claimed it was fine?
both questions I would have a better answer to if i had made some checks before fully powering up and fully connecting.
I MUST STRESS MYSELF TO REMEMBER THIS IN THE FUTURE.
but anyway now i am back at square 1. i have 2 mainboards that seem to be either both fine, or both broken in the same way.
what could possibly be going on here? how could a problem on the panel keep the mainboard from even generating the 12v to go to the panel? doesnt it need that before it can even detect an error?

oh i guess i should note that the replacement part we ordered did not have a picture of the tv displaying any image. the seller is not the most thorough with regards to that but i have got 2 good parts from them in the past. there is a chance this third part is just broken in the exact same way....

seriously hoping someone has some insight here!

could it be that the 12.7v i saw on the gate of that IC which needs to be brought low, gets brought low by some connection thru the panel cable to a ground on the panel itself, and that connection somewhere on the panel has severed?
i tried tracing where that gate pin gets its signal from and i could only get as far as the 2 tiny mlccs next to it before it disapears. im in diode mode with one probe on that pin and just caressing every pin and solder blob i can think of on the board and dont hear any beeps except on those 2 caps, which are not shorted.

am i crazy?