Samsung QN75Q60TAF Boot Loop fixed but no picture

[Nicktronic]

Hey, I have this Samsung TV that originally had a boot loop problem. I've isolated the pins on the ribbon cable to the panel board to stop the looping. I can hear the music on startup and when I move through menus with the remote, but there is no picture. I'm wondering what pins/signals I should look for that enables the Main Board to provide the video? Is it possible the main board is damaged? Anybody have experience wtih this type of issue?

Thanks!

[nomoresonys]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

https://www.badcaps.net/forum/showthread.php?t=39740

[Nicktronic]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

As requested

[Diah]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

why did you make the mask ?? if you just disconnected the LVDS complete did it still in boot loop.... also if you disconnect the cable between main boards and power boards did the LED BL light on bright ??

[Nicktronic]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Yeah, I disconnected the LVDS first and the looping stopped. Haven't tried disconnecting power cable, how does that help with the video? I want to check voltages vgh and vgl, but can't identify them on the main board.

[nomoresonys]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Why are you fighting? do the tests as requested. Diah will not request a test that isn't needed, it's all a part of troubleshooting.

[Nicktronic]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Didn't realize I was fighting, just didn't understand the relevance.

I unplugged the cable and yes, the BL came on full brightness immediately

[Diah]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

so you have short circuit on Panel. if you are lucky the short at buffer boards. it worth if you just consider working first on panel buffer boards with out LVDS in place test low R on caps / test or remove ESD diode...

[nomoresonys]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Picture #2, need picture of the whole board, done with 2 pics. if needed.

[howardc64]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

so you have short circuit on Panel. if you are lucky the short at buffer boards. it worth if you just consider working first on panel buffer boards with out LVDS in place test low R on caps / test or remove ESD diode...

Indeed, I fixed a QN50 recently similar to this. Shorted cap on buffer board. I recall googling for solution finding fairly common problem on QNs..

OP should followed the masked pin traces on the buffer board and likely find shorts. I used a FLIR with voltage injection and found it instantly

https://www.badcaps.net/forum/showpo...6&postcount=84

Read post #86 for debug process and solution.

[nomoresonys]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Indeed, I think Diah and Howardc64 are right on target.

[Nicktronic]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Pins 35, 36, 37 are what's taped off fyi. I don't know if i can trace to a specific spot, i don't the close up gear to follow the traces, but i'll try.

[Nicktronic]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

The rest of the pics

[Nicktronic]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Ok, so see the attached picture. Pin 37 doesn't matter. Pins 35 and 36 both need to be isolated to stop the loop. These pins go to the test points indicated in the picture. I'm hopeful that DT601, DT602 or IC601 is the culprit.

What are these chips and how should I troubleshoot further?

[Diah]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Ok, so see the attached picture. Pin 37 doesn't matter. Pins 35 and 36 both need to be isolated to stop the loop. These pins go to the test points indicated in the picture. I'm hopeful that DT601, DT602 or IC601 is the culprit.

What are these chips and how should I troubleshoot further?

we don't have panel diagram... the ic spi. follow the pins 36 35 on MB side to see their circuit. i think they are VDD 3.3v if thus case then no bootloop but screen remain black.. so the short at other place

[nomoresonys]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Maybe look up the datasheet on DT601,2, unless someone remembers how to test them. The shorts can happen in the panel itself or those panel driver boards.

[Nicktronic]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

In the pic in post #14, I see VDD3V3 above IC601. Also, see new picture for the text on top of the chips. I can't really find much except maybe BC1 is a voltage regulator? Can't find a datasheet

[lotas]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Bc1 - dt1042-04so (4 CHANNEL LOW CAPACITANCE TVS DIODE ARRAY)

[howardc64]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

Ok, so see the attached picture. Pin 37 doesn't matter. Pins 35 and 36 both need to be isolated to stop the loop. These pins go to the test points indicated in the picture. I'm hopeful that DT601, DT602 or IC601 is the culprit.

What are these chips and how should I troubleshoot further?

You can trace the masked off pins in 2 directions

- Towards main board to see if can find labels for what they are
- I don't know if main board's t-con section will boot far enough without LVDS connected, but perhaps try that and read voltages on the masked off pins on the main board to get a clue.
- Follow the test pads on the buffer board further to see what they are connected to.

Can also just check all caps on buffer boards for shorts using mult-meter with beeping diode mode (+ - probe on both side of every cap). If beep continuously, then you've found the shorted rail. But still need to find the shorted component on the rail usually by various combination heat method (touch, isopropyl evaporation, FLIR, voltage injection)

[Nicktronic]

Re: Samsung QN75Q60TAF Boot Loop fixed but no picture

See attached pic. I was trying to follow pins 35/36 on MB, but they disappear into the holes, and they aren't on the other side of the board. In my search, I found shorted caps (everything circled in orange) and a resistor? called R82 2029. Thoughts?