XBR-65X850D Backlight/Power On Help

[BoardHoarder]

Currently trying to save a 65” 850D that definitely has a main board issue. Power supply has standby voltage and PS ON pin shows 3.5VDC but main has no signs of life…..no light under Sony logo and no optical port lit up. 12VDC is created by main board but no input triggers from main = no TCON 12V and no BL ON voltage present. I know about the trick of pulling the main to trigger the test pattern from the TCON but I get no backlight. If I jumper the 3.5VDC to TCON ON and BL ON, I can shine a light on the panel and see solid green, red, blue and white cycling. The 4 + backlight pins on the power supply show 70VDC but none of the negative 8 - pins seem to have the signal ground for the LEDs. Meaning if I put my negative meter lead in either of the negative pins on the power supply I read 0 volts. If I use chassis ground of the panel for my meter lead, I read 70 volts at the positive backlight pins. If I jumper the 2 negative pins for the LEDs together and use an LED backlight tester and probe the corresponding positive LED pin, I can get a quadrant of the screen lit to see the test pattern from the TCON onscreen. So what I’m really wondering is, am I missing a trigger to force the backlight on or do I have a power supply problem in the LED driver section of the power supply? Substituting LED power with the tester gets me light but I’ve read that these sets have backlight issues as well. I really don’t want to pay for a main board repair plus LEDs plus maybe a power supply repair. TV came from a customer so I’m not sure what the event was that made them dump it.

[nomoresonys]

Post good straight on pictures of each board and one of the whole back as to see how everything is connected, post ALL voltages from connector you got ps-on voltage from, form it as ps-on 3.5 v etc.

[mmartell]

...I know about the trick of pulling the main to trigger the test pattern from the TCON but I get no backlight. If I jumper the 3.5VDC to TCON ON and BL ON, I can shine a light on the panel and see solid green, red, blue and white cycling...

How exactly do you do this ?

[BoardHoarder]

How exactly do you do this ?

I’m not sure when Sony started this but in this model and newer ones if the TCON doesn’t see video from the main board, it starts running a test pattern which basically tests the panel, backlights and power supply. Solid colors appear on the screen every few seconds and is helpful as a quick test. I know that I have more problems than just the main board because I have to still jumper standby voltage to BL ON and TCON on to get the test pattern to show up and the TV will not power the backlight. If I substitute using an LED tester to power a quadrant of the screen, I can see the test patterns on the panel. I’m just confused as to why the power supply won’t power the backlights. Maybe I have to do something with the BL_ERR pin or something?

[EazyBone]

I have a 850e with this exact problem. It's likely the emmc chip. I cannot jump the BL on either but I have tested all the 4 connections to the strips and the LEDs do work. I have seen on a few tvs where the BL from PSU would show voltage properly but wouldn't activate the BL because it was waiting for some signal from the main board, one which the PSU can't supply when jumping only bl on. Check out nicks TV on YouTube and look for Sony models, he will say that he immediately knows it's main board because of the rate of failure of emmc corruption

[BoardHoarder]

I have a 850e with this exact problem. It's likely the emmc chip. I cannot jump the BL on either but I have tested all the 4 connections to the strips and the LEDs do work. I have seen on a few tvs where the BL from PSU would show voltage properly but wouldn't activate the BL because it was waiting for some signal from the main board, one which the PSU can't supply when jumping only bl on. Check out nicks TV on YouTube and look for Sony models, he will say that he immediately knows it's main board because of the rate of failure of emmc corruption

The thing that doesn’t make sense to me is if you can take the entire main board away and get the test pattern with backlights, there can be no signal coming from the main. Most sets that I fix are LGs with LED strip replacements or Samsungs with main board issues and I don’t see a lot of Sony to know all of their quirks but I have watched Nick’s YouTube videos. I fixed a main board issue in a 55X900F that did give me the test pattern that was slightly different than what I’m seeing on this D-series. In the 900F the main was fully out of the set and I got the test pattern with backlight. I don’t repair TVs for a living obviously but if people are trashing them and I can fix them cheap, I give them to relatives and my neighbors have bought a few from me. I can’t do the EMMC fix myself and don’t want to throw money at this TV to find an issue with the backlights. There are 4 positive backlight pins on one connector and 8 negative pins in another that don’t give me a voltage reading across them but using the case of the TV as ground, the positive pins read 70 volts DC. I did see another of Nick’s videos where you can move a pin in the connector to force the backlight on in a red blink code error for shorted LEDs. I wonder if that’s what I’m missing?

[EazyBone]

That's to bypass the 4 or 6 (can't remember which code) error code. This was done when psu is giving bl_err pin voltage and you take it out and ground it. Sonys will do exactly as you say when you use tcon on bl on etc and bls will come on.
the model I have which is the E version, all of the lights were tested with led tester and they All work. So I know that's not my problem. I can't get the test pattern to run. So I don't want to throw money at it either cause I can't actually test the panel.

Spending that $100 to fix the emmc problem which is probably 95 percent your problem is kind of a gamble I know. But I'm sure you can stick the board in eBay for $150 after it's fixed if it isn't your issue, mainly because you will rarely see this board (at least mine) on eBay because of how common they fail is my guess.