Samsung un58tu7000fxza - Power cycles with no picture, only backlight

[cheebster]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Hello, just picked this same tv with the exact same behavior.

I wonder, how do we actually find out whats wrong on the panel or panel pcb/cof, is there anything we can do to find out instead of randomly using tape?

I tried checking various things with the meter, but no dice, missing some skills it seems.

[nomoresonys]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

you can test the capacitors on panel driver board, pretty simple:

so you check for very low ohms, go ahead check in circuit, meter set to ohm scale put a probe on both ends of capacitor would expect well over 100 ohms, can check for shorts, meter set to diode/continuity mode, put a probe on both ends if you get 000 or close to it it is shorted, can also check by putting neg. probe on ground, pos. probe on either end of cap, one side will give a reading other side will read 000, if both sides read 000 or close to it it's shorted. THIS TESTING DONE WITH TV UNPLUGGED FROM POWER.

[cheebster]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Hi there! Yes i already checked all caps for obvious shorts. What's next?

[nomoresonys]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

what were the results of test in post #32, does tv stay on, anything on display?

[cheebster]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Yep, tv stays on. Also, taping a bit of the connector between the 2 pcb's on the panel going to the right side of it makes the tv work, but no display. Sounds works, and tv stays on

[nomoresonys]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

you have backlight? or the backlight comes on and stays on with cable from powerboard to mainboard unhooked?

[cheebster]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Yep

[nomoresonys]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

so you have backlight with everything hooked up, just no picture?

[cheebster]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

No, i have backlight and sound with the lvds disconnected from the panel, or with tape on the U connector going to the right side of the pcb at the bottom of the screen, taping a few pins.

How do we find out whats wrong on a panel, ive seen videos where they disconnect power going to the panel itself by cutting a trace or
removing a resistor, then injecting 3.3 or 1.8v on the proper line, then checking for heat on the PCB of the screen, finding then the bad component

[nomoresonys]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

its advanced, some can not be repaired, many of those guys on youtube really know their stuff, you need to do the voltage testing to see whats missing, then follow their directions, weather it be trace cutting or wired coff bypass whatever the case may be, the one guy even used 100 x magnification for some of the repairs but most don't need that much, many videos there on testing and expected voltages, it will be a challenge but very rewarding if you are successful, it's not brain surgery but seems very close.

[cheebster]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Yeah. Well ive already used similar techniques on iphones and ipad board to find shorts, injecting voltage and finding the heating source or heating component. I'd like to do the same on this panel. Can the COF chips be replaced, or it's impossible ?

[nomoresonys]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Some on youtube claim success, others claim you need the bonding machine, I haven't tried such a task, looks very tedious, since my 20/20 vision is gone now, the stuff that takes keen eyesight I have to stay away from, I get a headache before I get 10 minutes into it.

[cheebster]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Well well, it seems a bit tricky to replace a such chip, definately a no-go. But are the chips really at fault ?

I noticed, on this one here these seems to be 5 test points, which i scratched (novatek nt30222h)

[nomoresonys]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

https://www.youtube.com/watch?v=8A1TPmJ4Eko

[nomoresonys]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

I usually just take it apart as much as needed to get to the boards then have a real close look at the cofs, most of the time I have had a bad cof it was visibly burnt or dark and mishaped, compared to the others, could be hotter or colder than the rest too.

[cheebster]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Yeah, i tought about this, check for burnt areas or heat, but since the panel doesn't stay on, my thermal camera doesn't show anything on the cofs.

Here are additional pictures on this model, there are these test points, but idk how to use them

[cheebster]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

i see there testout-cof1,2,3 and lc1 lc2 vgh vss, ck1-8, clr, stv.. anyone has a clue how to check stuff on there ?

[nomoresonys]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

https://www.youtube.com/watch?v=DiW6nNk1TYA

[pdsterns]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Update: After blocking many traces I was not able to make any differences with the screen. I did have the instruction voice speak some different phrases about setup but there was nothing I could do. I carefully looked over the tcon strips but could not see anything wrong with them, I flexed them and tapped them but nothing changed. I think I am snookered here. Does anyone out there know of anyone who tries to repair these tcon strips? I just hate to toss this 2 year old TV

[cheebster]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

We're at the same point it seems. Whenever i block traces, i get a black screen. It's like we are blocking lines that are needed. I'd really like to fix this one, not for the tv itself, but just for the heck of understanding what's happening.