Vizio M557-G0 1/2 panel VGHD LC1 (and maybe XON VSSQ LC2) Problems

[howardc64]

Failure Symptom

No Display. Just random blocks of grouped vertical red lines.
Disconnect right 1/2 panel (rear view), left 1/2 displays properly

Masking T-Con Signal Diagnostic

Reduced masking to 5 signals on right 1/2 panel and get perfect picture

Pins are

1 GND
2 VGHD
3 XON
4 VSSQ
5 LC2
6 LC1

VGHD and LC1 masking is absolutely necessary to get working panel. Didn't unmask 3-5 individually.

Pictures and Schematic

XON, LC2, LC1 are on AUO s302-21 32pin QFN (PDF pg 66 of this HiSense service manual link has pin out)



Any Better Repair than 5pin Mask?

3 caps on the lower left rectangle labeled "A" on buffer board are connected to the masked pins. Removing these might produce same repair results. If same, I'll just keep the 5pin mask repair.

I guess right 1/2 panel higher voltage gate potential line circuit have problems which is why masking them off fixed the TV

WiFi/Bt also doesn't work

Service Mode TV Info seems to show no WiFi/Bt HW. But HW is present on the main board. Factory reset and update to latest firmware did not resolve.

[Diah]

the most common ESD diode got defect as this section

[Diah]

colored vertical lines always caused by shorted caps
i would disconnect panel from t-con and start test the suspected caps related to masking of low ohm

[howardc64]

colored vertical lines always caused by shorted caps
i would disconnect panel from t-con and start test the suspected caps related to masking of low ohm

Thanks, I'll check more carefully, didn't find any shorted rails on initial buffer board check. And the 5pin mask solution didn't work long. Once something warmed up, got failure again.

[Diah]

the wide black line location are the issue at cao

[howardc64]

the wide black line location are the issue at cao

What is CAO?

Found 2 caps with low ohm / short to GND on both sides. Removed the cap and low ohm/short is still present. No short on both cap. No other short / low ohm caps on buffer board.

• Section A, B, C on buffer board are examined
• Section B y is 5.2 ohm to Section A x. x pin on flex connects to GND on T-Con. Cap is not short.
• Section C cap pads measure 180ohms without cap. Cap is not short
• Examined COF in section A,B,C. No burn marks on flex or COF.
• FLIR video of buffer board shows only hot spots are COF and occasional metal reflections.

[Diah]

What is CAO?

look on yours keyboards you will see O are close to P LOL.... fast writing

yours photo which show 180 ohm...they are not caps just 0 coil R --- put them back

check the area of this section at yours FLIR section

[Diah]

the most common ESD diode got defect as this section

[howardc64]

the most common ESD diode got defect as this section

Thank you much for the hint. Fixed, 2x diode shorts on D14 ESD diodes was culprit. Removed and shorted cap circuit nearby disappeared. TV works with no t-con signal masking. Also found same fix in this thread ( link ) Don't have 4264H ESD diode array ( link from prior thread ) in my donor buffer board pile. Seems unnecessary but probably good to put good one back for ESD protection?



4x thermal rectangles in post #6 are just 4x groups copper pads reflections.

[howardc64]

UPDATE

Replacement ESD diode array ( link ) came in. Replace D14. TV continues to work as if it was removed before but now with ESD protection. D15 had no OL issues and works. Was a mistake in prior measurement. Some people claim can remove and put on by soldering iron. Would need a really good micro pencil with a knife tip and probably some low melt solder. I just used hot air station (should protect the gold flex connection below from hot air).

These are commonly called TVS (Transient Voltage Suppressor). Note there are other TVS with same form factor and pin out but most are for low voltage high speed communication signals such as USB3 and HDMI. These can't handle > 5-6v. D14 handles close to 30v with VGH so need to get TVS with higher breakdown voltage rating such as the link above.

[Diah]

good done to replace it... its not just you write., its belong to gate Transistor for discharge and provide currents linted when the resolution changed-

[howardc64]

good done to replace it... its not just you write., its belong to gate Transistor for discharge and provide currents linted when the resolution changed-

Thanks. So I guess important to replace with correct TVS (Transient Voltage Suppresser for those not reading prior posts) than just remove.

Also I guess valuable to salvage buffer boards from cracked screens for spare parts my spare buffer boards were older TVs and didn’t have this particular TVS.

[Diah]

Also I guess valuable to salvage buffer boards from cracked screens for spare parts my spare buffer boards were older TVs and didn’t have this particular TVS.

exactly this what i did