Vizio M557-G0 vertical red lines

[mightymos]

See attached photo for symptoms.
Supply board produces +18V on output pins and shows no fault with ~3V on fault pin. Backlights come on.

I replaced two 220uF capacitors on main board because plugs might have popped a little underneath (hard to tell) but no change in symptom. Main board has two UART headers which I soldered connectors onto, but do not see activity on either with scope.

I've tried wiggling connectors around unit when powered on but no change in symptoms.

[nomoresonys]

Re: Vizio M557-G0 vertical red lines

make sure cables to tcon are clean aligned well and not loose fitting, and maybe test tcon voltages to make sure they're everything they should be.

[nomoresonys]

Re: Vizio M557-G0 vertical red lines

maybe test the little caps on panel driver board for shorts or low ohms.

[nomoresonys]

Re: Vizio M557-G0 vertical red lines

If you can bring up a menu, see if it also effects the menu display.

[mightymos]

Re: Vizio M557-G0 vertical red lines

As far as I can tell I reseated cables and they seem okay.
I can get TV to respond to button presses for power and maybe display changes when I push other buttons but no intelligible display.

I have the 55T32-C0L board.
The problem is I can only find one datasheet for RT7277 step down converter, though other switching regulators seem to be present. There's one other datasheet found for serial flash.

The voltage feedback divider is a little different than datasheet and uses three resistors, two in bottom branch in series. In circuit both divider legs measure 7Kohm, so I think output voltage should be about 1.5V. It shows 1.2V on scope but isn't wildly different I guess. Might make sense that I'm just misinterpreting layout or in circuit is messing up measurements.

There are five capacitors on Vout, in circuit they show 50 ohms across which seems low. However there's also a resistor [18A] code across them which would apparently mean 150 ohms.

I'm possibly considering replacing tcon board from jimmy but can try other troubleshooting steps.

[nomoresonys]

Re: Vizio M557-G0 vertical red lines

maybe check voltages of tcon, VDD, VGH, VGL, VCOM.

[nomoresonys]

Re: Vizio M557-G0 vertical red lines

you probably already did, can test for voltage going in and coming out of tcon.

[mightymos]

Re: Vizio M557-G0 vertical red lines

you probably already did, can test for voltage going in and coming out of tcon.

I finally paid attention to silkscreen and noticed labeled test points.

AVDD 15.12 V
VSS0 0 V
VGHD 24.8 V
VGH 24.8 V
VSSG -7.9 V
VCC 3.3 V
V3D3 3.3 V
0_TCON 1.8 V
1_TCON 1.1 V
V12 12.2 V

[mightymos]

Re: Vizio M557-G0 vertical red lines

you probably already did, can test for voltage going in and coming out of tcon.

Hey sorry, any of my voltage measurements in the other post seem suspect? Did I miss any measurements?

[nomoresonys]

Re: Vizio M557-G0 vertical red lines

might need more opinions but they seem ok.

[mightymos]

Re: Vizio M557-G0 vertical red lines

might need more opinions but they seem ok.

Thanks so much for taking a look.

[nomoresonys]

Re: Vizio M557-G0 vertical red lines

well if tcon is ok, guess I would suspect the mainboard.

[mightymos]

Re: Vizio M557-G0 vertical red lines

well if tcon is ok, guess I would suspect the mainboard.

I initially ruled it out since they board seems to be getting +18V and fault line on power supply shows high level (good) (but guess that just means led drivers are okay). I'll try to check supply voltage on main board, tough without a schematic. Any advice where to start?

[nomoresonys]

Re: Vizio M557-G0 vertical red lines

mainboards can be a tricky animal, some testing there, there's lots more on youtube also:

https://www.youtube.com/watch?v=ocqnqmBxiqY

[nomoresonys]

Re: Vizio M557-G0 vertical red lines

have been having bad luck fixing boards lately, even powerboards.

[mightymos]

Re: Vizio M557-G0 vertical red lines

have been having bad luck fixing boards lately, even powerboards.

Thanks for the attempt though.