Samsung QN75Q6DRA, No Picture, Has BL, and Sound

[Dodgethis]

Ya Nomo, I agree I won't be buying a Samsung in the future. I'm not impressed that this TV was once over 2k USD, and now its a glorified paper weight. I tried to warn my parents about the quality, but alas they bought another Samsung.

Lotas, I've included photos of the ribbon U cables.I shot gunned from the hip, and masked the last driver board on the left side, and that stopped the boot loop. I believe your on the correct path regarding the left board being an issue, as I was testing and with the U ribbon cable connected the picture degrades. The picture is crystal clear when the left U Cable is disconnected.

Having a blast so far guys, hope this helps someone in troubleshooting their similar model.

[lotas]

Remove the tape, it's not visible, or it's been masked.

[Dodgethis]

Here you go Lotas

[lotas]

Here you go Lotas

It could be better quality, these conductors are hard to see... The one I posted above is good, but with tape...

[Dodgethis]

Your needing to see traces inside the cable? I figured you needed to see the gold contacts. I'll work on a better photo

[lotas]

Yes, I am especially interested in these thin lines with contacts.

[Dodgethis]

Hows this?

[lotas]

Here you need to experiment with the contacts to achieve a better image, try masking these ones.

[Dodgethis]

Hey Lotas I masked those pins, The picture didn't degrade, still have a black portion of that side of screen, Safe to say that's the dreaded dead zone?

[lotas]

Yes, this short circuit (0.2 Ohm) is located in this part of the screen, so you need to calculate it (which signal it is and mask it, try moving it a little to the edge, in general, excrete it, reduce the tape to a smaller number of contacts...

[Diah]

if he had point on buffer...with DM on continuous check it to the U ribbon pins to know which it belong and mask the only pins

[nomoresonys]

if he had point on buffer...with DM on continuous check it to the U ribbon pins to know which it belong and mask the only pins

Looks like an interesting technique to try, can you describe how to?

[Dodgethis]

Looks like an interesting technique to try, can you describe how to?

Hey Nomoresonys, I "thnk" if you look at post 31, If you pick one of the two points off the board.( Preferably the pad where the transducer is lifted) Where the illustration is showing the transducer being lifted by one leg. If you had a dmm on "continuity Beep mode" and say black lead on that pad on the board and the otthe red lead checking each point on the U ribbon cable, or Lvds cable it should beep showing continuity and you could mask that area quicker than blindly moving tape at a section hoping for the best as you test it.

Lotas /Diah please correct me if im wrong.

Lotas /Diah

Would you guys know whats important not to mask to provide picture on the screen? I have moved the taped normous times, Tried the above mentioned, and was curious if I provided voltages of the driver board, would yall be able to point out if they are not normal?

[Diah]

i didnt catch what you mean.... as i read before you have some where point on the buffer boards read low 0.2Ohm with chassis.... where are this point?

[Dodgethis]

i didnt catch what you mean.... as i read before you have some where point on the buffer boards read low 0.2Ohm with chassis.... where are this point?

Yes your correct, I had to go back and check myself. I was mistaken, I don't know how I got 0.2 ohms, but from the top pad of the transducer to the chassis I have open line. So no short. I wanted to ask. shouldn't i be measuring 17 volts DC at some point on the Driver board? I "think" im missing AVDD voltage which should show 17 vols. They highest voltage i found was roughly 8 volts.

I check the working side of the TV, and it shows on the first smd capacitor that it has 17 votls, however I never get close to that on the black picture side on the driver board. I'm hoping this is a driver board / smd CAP issue.

I went as far as checking Winbond IC chip that is the driver board that connect with U ribbon cable to the suspect driver board, and Its receiving 3.3 on VCC pin.

How do we find AVDD? I've posted a photo where its shown on the driver board, but where is a measuring point for it?

[Dodgethis]

Giving a quick update, Still working on TV. I'm trying to fix the right side of the screen that is black. I purchased a LCR tweezer that could read the capacitors in circuit. I didn't find any shorted caps, but the tweezers can tell me the ESR of the cap's. I used Diode mode and had the red probe on a chasis ground and used the negative probe to find any shorts on the caps on the buffer board. Going to find VGH and VGL, and will report back my findings. If anyone is curious the tweezers are called FNIRSI LCR-ST1 10KHz LCR Meter.

[Dodgethis]

Ok, So i have probed for voltages. Using the black lead on the chassis ground, and using the red probe to grab voltage readings. I started in the direction of the arrow, and stopped mid way as I have a question. What are the crucial voltages that the panel has to have to show a picture? I understand VGL, VGH, and AVDD is important but which are crucial? When the tv Powers on, the right side seems to show a dark blue background when the samsung logow shows up, then turns black.

From where I started per the attached photo, and per the service manual looks like i'm starting at pin 94 due to the first reading is 17v so its AVDD. Do these values seem off to anyone? I didn't finish all the points, but wanted to know if what i had is suspect and if my thought was correct.

By the way, what does Portnum, or Demura mean?


17.03
17.03
16.21
9.04
8.47
8.47
7.56
0.395
1.872
1.873
6.6v
3.336
0.084
0.084
0.079
0.085
0.141
7.07
0.071
7.06
-3.06
10.81
11.45
0.06
7.23
-3.10
6.90
.06
6.92
.00
.00
10.34v
0.0
0.0
1.785
stopped lost my place and measured the last point which was 3.33v marked red arrow at the end of connector on photo

[Dodgethis]

Ok, took a step back, and looked at the main board with it disconnected and off the panel tv. I found some test points to probe with it hooked up and powered on. The values measured is with the jumper installed to produce voltages to the panel. I have the following: VGHD is zero at the test point. I thought VGHD was needed for left CN1300 only but shows it on the right connector CN1301 per the service manual. Still hunting....i was hoping that would be the smoking gun, but i suppose not as the right side produces an image looking at the rear of the TV.

vgh = 30v
havdd = 8.5v
avdd = 17v
vcca = 1.9v
vccab = 1.9v
vghd = 0v

[Dodgethis]

Figured it out. So where I thought the buffer board was bad after countless checking for a problem, and couldn't find one, and looking on the main board for problems, and couldn't find one. I found out why the right side was showing no picture but had back light and sound. I checked for voltage on the first smd capacitor closest to the U Jumper connector. I kept reading 8v but never the 17v like I could measure on the last buffer board on the left side that was working. I got very close in doing a voltage injection with a 9v battery, or a jumper wire from one working point to the other that was missing the 8 volts to make 16v. I took the U connector off and found i had masked a few pins that i wasn't aware i had, and bingo i was able to measure 16VDC. I have a picture, and had to mask 1 pin on that right front side to work. It is a clock signal.I hope this helps someone.

Guys thank you for your knowledge, and input i've learned alot, and enjoyed figuring it out