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Vizio VT420M - power problems    
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Joined: 29 Aug 2014
Posts: 1
Location: Denton, TX

PostPosted: Fri Aug 29, 2014 6:33 pm    Post subject: Vizio VT420M - power problems Reply with quote

Vizio 42 inch LCD HDTV, purchased in 2010.
Model : VT420M
Issue: Possible main board problem

I will try and make this as detailed and brief as i can.

My first notice that anything was wrong with this set was in the first year of owning it. It was a minor issue so i didnt think much of it since Vizio customer support was notorious for giving more trouble than it solved. If my Xbox360 powered down from the sleep timer the sound would not play upon turning it back on. I would have to unplug the HDMI or turn the TV off and then back on to restore sound. Since this didnt happen often it was easy to shrug off.

In the last 2 years though this has progressed to the screen not displaying anything after the Vizio logo flashes quickly on the screen. Some cycling of the power has usually resolved the problem but it has been getting steadily worse. So much worse, in fact, that the last few months we have avoided turning it off at all except quickly to restore sound. Once its working we can leave it on and as long as its not turned off for any length of time it functions normally (except the sound glitch).

Logically im thinking there is a video/audio board malfunction. If the LCD was bad it wouldnt display the Vizio logo at the beginning, it also wouldnt function normally indefinitely if it was just left on, the image would go out eventually. Last night i goofed and turned it off, out of reflex, while shutting everything down for the night. Now today i cant get it to come back at all. Sound or image.

The backlight is on, and I've tried replacing the T-con previously to no change in function. With the sound gone now that seems to lend support to the video/audio theory. Any suggestions or advice for someone trying to save their TV without spending more than he can afford?

Thank you in advance for your time and expertise!

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Joined: 21 Jan 2009
Posts: 2395
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PostPosted: Sat Aug 30, 2014 1:24 am    Post subject: Reply with quote

IF replacing the Main board cures (presuming you can get the correct one), I suggest NOT using HDMI (use Component instead).

Joined: 28 Dec 2006
Posts: 2879
Location: Overland Park, KS

PostPosted: Sun Aug 31, 2014 4:53 pm    Post subject: Reply with quote

I've worked on this model before. the mainboards are total crap. heat causes the main processor on the board to detach itself from the board. It's very temp dependent, so it doesn't surprise me that it keeps working if you leave it on (warm). mine was the opposite where it lost video after it warmed up, but it would work for a short time when cold.

At the time I was working on it, new boards are not available. Someone was "refurbishing" them online for ~$180 with a very short warranty to back it up. I was able to find a used one on ebay and told the owner that it was a crap shoot with no warranty. They were fine with this and it has worked out well for them.
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