Hisense 55h8f, standby ok, not turning on

[moosets]

Symptoms: Not turning on after pressing power button on tv. Standby red light on power button turns on when plugged in. Pressing power button on tv causes standby led to turn off for 2 seconds, and then back on red until power is removed (no longer responsive).

Tried: Removing power, holding power button, returning power. No change.

Power supply: 244194 RSAG7.820.8805/ROH
Main board: 244187B, RSAG7.820.8833/ROH

Opened back and inspected all boards, no obvious damage anywhere.
The power supply is making a slight clicking noise, maybe a symptom?
Measuring the voltages:
Before power button press:
12V low: 9V
18V low: 16V
STB: ~0V

Thanks for any help

[dskall]

Re: Hisense 55h8f, standby ok, not turning on

Could use some good pictures of boards

[moosets]

Re: Hisense 55h8f, standby ok, not turning on

Shopjimmy has some good high res images here https://www.shopjimmy.com/hisense-24...-supply-board/

Here are the boards on my tv

[moosets]

Re: Hisense 55h8f, standby ok, not turning on

Ordered a new power supply and tv has the same issue so it rules that out... Main board is suspect?

[moosets]

Re: Hisense 55h8f, standby ok, not turning on

So I used an oscilloscope to probe around and it might have gave me a lead. I was probing the power supply connect XP812 to the LED driver board and I am seeing transient behavior, as though something is possibly shorted?

In the attached screenshot I have a probe (yellow) on VIN on XP812 and the other probe is on SW, I think it was. So you can see at the beginning when I plug in the board, the VIN voltage peaks and when decays to 0 (though I press the power button before it fully reaches 0) and I press the power button around t=0s, and VIN goes high, about 3 seconds later SW goes high to about 2.8v and there is a dip of VIN, about where the TV locks up and becomes unresponsive.

Well, this seems to indicate a problem with the LED driver so I began probing around on that board. All voltages to drive the LEDS seems to be ok except this one pointed to on the picture, this one is outputting 6.5v... What do you think, bad IC?

[alfatv]

Re: Hisense 55h8f, standby ok, not turning on

Did you check backlights?

[neilc6]

Re: Hisense 55h8f, standby ok, not turning on

I would suspect backlights as well with any TV turning on or attempting to turn on with flash of backlights or no backlight.