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75" Quantum 4K ULED Hisense Android Smart TV (2020).

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No image: backlight and audio working. Replaced Tconn didn't fix.

There are sub-models....this one is G194998. Link below are the parts. I have verified each board number and graphic in that link match my own, so you can use the images there.

https://hisense.encompass.com/model/HIS7...

IMAGE: No image, but all else seems to work.

BACKLIGHT: I can see many of the LEDS from behind when powered with back removed. I can also get the general "full screen glow" from the front when powered. And the "full screen glow" changes intensity as I click through menus....so sure seems to be working.

AUDIO/MAINBOARD: both seem to be working fine. I can select a remote shortcut for Netflex and even start blindly playing content and hear the menu clicks and content, for example.

POWER: No bulging caps or obvious damage.

TCONN: I was so supremely confident it was the Tconn board based on the symptoms that I just ordered one and put it in. Then shocked/disappointed to see the problem remained.

One, small clue. About 8 months ago this same issue was happening.....and the fix for a while was to leave the TV powered for about 60 seconds, then turn it off and immediately back on again. This always restored video to operation, but I suspected the Tconn and ordered it. But then I never replaced the Tconn because for about another 6 months it just worked on the first try every time. Until last week, all of a sudden the symptoms returned and the warmup/power-cycle trick also failed me. So I put in the TCONN fully expecting the issue to resolve....but nope. Still no image output.

Not sure where to go from here. I can blindly try to replace the power or mainboard. I've very disappointed in Hisense as I called them when the problem first started occurring but I was just a few months past 12 month warranty. TVs should last longer than that....

PS: I'm an EE with some amount of tools and skills, but contrary to family beliefs that doesn't necessarily translate to a master of modern home electronics repair.

Boards Layout:

Block Image

Power:

Block Image

Backlight Driver

Block Image

Tcon:

The below conneted /covered. The board above is the one just removed/replaced.

Block Image

Main:

Block Image

Other items of note:

  • I have removed, reseated all connectors and wiggled them a bit during operation to look for anything faulty.
  • I checked all power with a multimeter with the labeled voltages. Everything was correct with the exception of the indicated 13V to the backlight which very strangely reads near 29volts. The backlight board doesn't label a voltage input...just shows VIN. Still, the backlight and the local diming feature seem to be working (if I disconnect power to the backlight, the obvious difference of no backlight. if I disconnect the connection from backlight to mainboard, I get backlight but the backlight doesn't change on the screen as I click through menus I can't see...which I belive is the local dimming at work)
  • The main board takes 12V which is measured/correct. Again, I have audio and can hear it boot and navigate menus, so the main board seem to be largely working...even the local dimming control. Best I still get no image output.....even after replacing the Tconn.
  • At this point, all I can think of is changing out the mainboard....but I'm not sure I want to fork over the $300 clams and risk it not working.
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If you have no image on your TV or monitor, but the backlight and audio are working, and replacing the T-con board did not fix the issue, there are a few other possible causes that you can investigate:

  1. Faulty main board: The main board is responsible for processing and displaying the image on your TV or monitor. If the main board is faulty or damaged, it can cause the image to not appear. You may want to consider replacing the main board if you have already ruled out the T-con board as the cause of the problem.
  2. Loose or damaged cables: Check all cables connected to the TV or monitor to make sure they are secure and undamaged. Loose or damaged cables can cause image issues or prevent the image from appearing altogether.
  3. Bad panel: If the main board and T-con board are working properly, but the image is still not appearing, the issue may be with the panel itself. A bad panel can cause image issues, including no image at all. Unfortunately, a bad panel is usually not repairable and requires a full panel replacement, which can be expensive.
  4. Firmware issue: In some cases, a firmware issue may be causing the problem. You can try updating the firmware on your TV or monitor to see if it resolves the issue. Refer to the manufacturer's instructions or website for details on how to update the firmware.

If none of these steps resolve the issue, it may be best to contact the manufacturer's support or a professional technician for further diagnosis and repair.


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OK, so an answer of sorts. Did I mention I was a EE?

Basic debug principles = isolate, isolate, isolate. I started at the Tconn and disconnected both outputs one after the other. I immediately found that only one half the screen was the issue (the left when facing front). This Tcon output feeds two quarter-panel LCD screen drivers in series that have connectors similar to the Tconn. Disconnecting these one at a time, I isolated the issue to just the leftmost quadrant. Disconnect this quadrant and everything works on the remaining 3/4 screen.

Unfortunately.....here I stalled out. There are no further connectors....it's ribbon straight to the glass/panel. I even tried removing the bezel to be sure, but no dice. Tried cleaning with IPA and some mechanical pressure without luck.

It could be a short on this final driver board and not the panel itself. I ohm's across all the caps as there aren't that many, but nothing obvious. My conclusion is it's the LCD panel itself somehow (I didn't know, or don't have experience, with them failing like this)

The good news is that I can confirm the power-supply, mainboard, two Tconns (original and replacement one I purchased), backlight driver, remote, cable, wifi, etc are all working....so I guess I'll remove all these other parts and sell it on Ebay.

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Colin B first post some pictures if your boards with your question. That way we can see what you see. Next check all the interconnect cables for any corrosion, tears etc. Next you have to check the main board to power board connection. There should be one connector and the values « should » be printed on that. Let us know what those values are. Remember, it is the mainboard that tells the power board when and what to turn on (simplified)

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Hi,

If you're game enough, contact Hisense in your location and ask for the latest firmware for the TV. (example only - check for your location)

Like some other brands it seems that Hisense checks the USB port during startup for an appropriately named file and if there proceeds with the update before completing the startup.

The caveat with this is that some have said that when they tried this they ended up with a "brick" and the TV no longer worked at all as they think that they got an incorrect link or file

After that a new mainboard would be required as that is where the firmware is stored.

The safer method, which is not an easy option for you is to update via the TV menus as this will ensure that you get the correct one if there is one that is .

Perhaps since you can get online and that the only thing at the moment that seems to be at fault is the video, you can "step" through the menu screens "blind" to get to the update setting and try that.

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Colin B zal eeuwig dankbaar zijn.
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