Sony 4k TV XE8004 series backlight main board issue

[CuriousJohn]

Hi folks another doozie here,

Got this TV on my table this week and at first suspected a simple failing LED on the back lights as symptoms where backlight coming on at power up and within a few minutes flickering then failing other than that TV works fine.

This set is side lit and noted sometimes the flickering would start right away even during boot, after testing found backlights + inverter good. To cut a long story short found that applying pressure to specific spot on mainboard heatsink caused backlights to come on or off and even moving chasis about caused this other than that the TV works fine!

Initially thought a short to chasis or maybe bad cable between MB and PSU but lifted mainboard up and found pinching with fingers between back of board and heatsink in specific spot caused the lights to come on as pressure applied.. There is nothing really under the heatsink in this spot certainly nothing touching the heatsink and so wondered if CPU was needing reball, tried that and now have killed the backlights totally lol but the mainboard still works fine just mainboard appearing to not be sending the on signal.



Any takes on this mystery i really could use the pin outs for the mainboard at least to id the inverter on signal, schematic would be awsome is it about anywhere?

Cheers in advance CJ

Below is photo of mainboard with heatsink removed

1-981-326-12 (173633712) Main Board

[R_J]

Re: Sony 4k TV XE8004 series backlight main board issue

Sounds like a typical BGA problem on the large ic, Did you actually remove and reball the ic? or just heat it up.

[CuriousJohn]

Re: Sony 4k TV XE8004 series backlight main board issue

Hi thanks for reply, did some local heating with hot air carefully in attempt to reflow i think i said reball in op but got those two concepts mixed up and that totally killed the backlights anyway so havent removed the IC that would be the next step I guess and a first for me but im here to learn, might try another reflow before i do reball :-)

Last night i had a good look at the power distribution board im trying to determine the way the inverter is controlled to trace back the signal but as you say its sounding like the main IC and its sort of annoying that its just the backlight control signal that seems affected the mb still works but not stress tested.

i noted the inverter has 2 x 6 channel IC led controller BD9423EFV with the backlights being 64 led's split up into groups of 8, 2 of them IC's makes sense hoping the data sheet will show the control pin of the LED IC and can follow it back from these chips to the power connector CN3000 and from there onto the MB for what its worth.

[CuriousJohn]

Re: Sony 4k TV XE8004 series backlight main board issue

Ok had good result today the TV is up and running very well... I found the right pin to switch backlights on without any invasive action this will run the TV until or if the Mainboard does die but it has no other faults detected so far. See photo for solution, no backlight on signal from main IC so on power distribution board LD1 connected 1K resistor between Power up signal and backlight signal on CN3000 connector and it works a treat but not for the purists lol do it at your own risk i had to follow it all back carefully using datasheets the works to be sure.

[R_J]

Re: Sony 4k TV XE8004 series backlight main board issue

I guess that will work, only problem is if the original intermitint connection fixes itself again, the resistor feeding voltage back to the control ic could damage it.
These can be multi layer boards, so if its not a bga fault it could be a cracked feedthru from one trace to the other.

[CuriousJohn]

Re: Sony 4k TV XE8004 series backlight main board issue

The wire into pin 1 controlling backlights has been removed from the connector block and taped back just in case and did wonder about the multilayer board if something had gone OC. Didnt see point in attempting reball when everything else was ok if MB fails in time it can be replaced at that time and resistor removed no hassle.

Have run the set for 12 hours straight and apart from not connecting to wifi for a a few minutes (now working stable) it all works really nice and cracking image indeed its first Sony 4K i worked on like best image i seen yet but im usually sniffing around budget stuff. Was surpised to see things like spades not having covers on and such in the Sony thought that was a but cheapo even Vestel can manage that lol and yeah multilayer board is an ass to trace back but good learning tho cheers....

This LD1 power distribution board uses two 6 channel BD9423EFV IC which is a boost driver for the led backlights, found pin 17 the STB signal actually switches the N channel MOSFETs that bring backlights up by giving a ground to the backlights, two mosfets one for each chip and pin 21 pwm mastr slave setting both chips connected this pin togethor and this is what the motherboard talks to bring pin 17 on or off. Pin 21 needs at least 1.5v for backlights on according to datasheet and MB here was sending around 1V. Max is 20v so 3v all good. did consider tracing it back on the MB to but maybe thats for another rainy day.

[R_J]

Re: Sony 4k TV XE8004 series backlight main board issue

If it is working that way then that's good. cheap repair.