HDTV backlight (LED) repair

[tcsenter]

The backlight on Vizio V585X-H1 teleo went kaput a couple weeks ago. It is full array backlight, not edge lit. The whole backlight went, not a zone, not a strip. Using the flashlight trick, or just ambient light striking it in the right way, you can see there is a picture being sent and displayed to the LCD panel. I can even squint and move through some initial setup menus, after resetting the TV to factory settings.

According to troubleshooting stuff I've read, this combo of working display panel but total backlight outage on an LED TV should mean one of two causes; the power supply board OR the LED driver circuit. Or potentially both, I would assume could happen. The LED driver circuitry may either be integrated onto the power supply board or a separate LED driver board. The mainboard with the I/O and system/video processor IC and T-CON board can be considered working if the panel is displaying a picture.

I picked up a replacement power supply board and it no worky. So that would leave the LED driver circuit but I am unable to find it. It does not appear to be integrated on the power supply board? Or is it and I just don't know what to look for?





Unless the LED driver circuitry is on the underside of the aluminum shell on which the other boards are mounted? See the black cable (coming from PSU board) making a dive through a hole:




None of the parts dealers list any kind of LED driver board as separate circuit for sale for this Vizio V-series family/model. Could the T-CON board to be the culprit?

 

[mindless1]

I am wondering what is under the long narrow heatsink at the top left of the power board pic. Looks sort of like two DIP-8 chips?

Otherwise, IDK, am doubting there is a separate LED driver/control board, but I don't know this as fact.

One thing I'd do is hook it back up and measure for voltages on the respective labeled connector contacts, and see if you can find info on what V they should be. Don't electrocute yourself.

I would also wonder about this replacement board. Are you certain it was new or at least a working pull? I mean that if all these boards are likely to end up dying by the same fault, then someone could have just pulled the boards and sold them, not really knowing which was bad, so you now have two bad power boards?

I can't see any signs of heat-discoloration on the power board pic, but the top silver heatsink looks a little strange having grease smudges on it, can you tell from the soldering if someone has replaced those transistor(s) diodes?

 

[tcsenter]

Thanks I've decided to scrap it. All five videos I watched on YT are many years old now and appear to be based on TV models of a prior art that has been supplanted by newer designs. I'm just thinking, how do all five (or six) strips of LEDs stop working all at once? Sounds like a power supply issue but since that wasn't it (assuming this Ebay seller actually is selling "working" units) I am not really up to putting more time and effort into it.

 

[mindless1]

I noticed something on the power board pic, might not be a problem but I wonder if the NTC thermistor I've pictured, has a broken leg as there is a vacant hole there? Then again, I would have thought that is in series with ALL power input, so the TV wouldn't work at all if that NTC R is really broken.



The only way all 5 LED strips themselves would be expected to stop working simultaneously is if they were all in series, but I never see anyone mentioning a TV set up like that, instead the strips are in parallel to some extent.

 

[tcsenter]

No each leg has a little curly deal before it enters the through hole, it kind of is obscured by the angle.