Vizio VW37L HDTV20A No signal, then no picture

[skytoastar]

So I acquired the eponymous TV knowing the panel was still good but that it really didn't work. The TV will apparently start fine to a blue screen with the message "no signal" but if you connect a source (see attached), it goes black and then doesn't respond to inputs. Sometimes the blue image will fuzz out (see attached) before going black. It does this best when started cold. After running for a few minutes it fails to even go to a blue screen.

My hope was just to replace the main board by buying a replacement through eBay. After four months of patiently waiting, I never found one at a price I considered acceptable. Somehow I came across this forum the other day and based on what I had found on this and similar models, it sounds like the LDOs are a common failure point.

Now I list the voltages:
U19: 1.24, 2.48, 5.09
U15: 2.06, 3.31, 5.09
U17: 2.07, 3.32, 5.09
U44: 8.44, 9.69, 11.09
U16: 11.09, 0.00, 5.00 (silkscreen: IN, GND, OUT)
U22: 2.07, 3.32, 5.12
U20: 0.55, 1.79, 3.29
U26: 5.00, 0.00, 1.23 (very small 5-pin device)
U21: 0.00, 0.71, 2.48

I really only suspect U21. That one is an AMC1117 which is one chip others have had issues with on this model (based on my searches here).

I thought I'd just post this to make sure I'm not crazy about suspecting U21 and to make sure I didn't miss anything else based on the symptoms.

[skytoastar]

Re: Vizio VW37L HDTV20A No signal, then no picture

Also, based on the AMC1117 datasheet, I found two suitable replacement parts in my search on Digi-Key: NCP1117LPSTADT3G and AZ1117EH-ADJTRG1
Search parameters: 1A current, Adjustable output, SOT-223 or SOT-223-4, Active (not obsolete), in stock, available in quantities of 1, has 1117 in the name.

Are those suitable parts?

[skytoastar]

Re: Vizio VW37L HDTV20A No signal, then no picture

I replaced U21 with a AZ1117EH-ADJTRG1. It lives!

[budm]

Re: Vizio VW37L HDTV20A No signal, then no picture

Great repair, another 1117 failure. The minimum output of 1117 is always 1.25V, it cannot be less.
The output of adjustable 1117 = 1.25Vref + Adj. Voltage

[skytoastar]

Re: Vizio VW37L HDTV20A No signal, then no picture

It was my first attempt at surface mount soldering. I didn't really try desoldering the chip. I clipped the three smaller pins, bent it up, then used the iron to get the big tab off. Then I used the iron again to get the remains of the pins off the pads. Getting the new one on was easy after getting the first pin tacked down. I'm going to have to be more brave with surface mount parts in my own projects going forward.

[budm]

Re: Vizio VW37L HDTV20A No signal, then no picture

"I clipped the three smaller pins" That is one way of removing bad parts since there is no need to try to save the old part and it is better not to damage the traces trying to remove the bad parts. I add more solder to the big tab when removing the big part..