42" Vizio No pix, No sound
 

I just got a call from my nephew about a Vizio 42" LCD set (GV42LHDTV) that does not turn on. No pix or sound. A faint relay click can be heard and a white LED in the front of the set comes on, which may be dimmer than normal, but that is all that it does. The set is about 7 years old. Any ideas? What should I look for or check?
PS I have never seen the insides of a LCD set before.

Thanks,
jr

The general first thing to look for with a symptom like this is bad electrolytic capacitors on the power supply board. On newer devices like this, the caps are often easy to identify because they bulge on their tops.

Be prepared to remove a LOT of screws to get into the set, and maybe a bunch more to remove shield covers or other items inside it.

1) Get a couple boxes of good quailty .22 LR cartriges.
2) Get a good .22LR rifle, like a Ruger 10/22.
3) Place said defective video display unit in a suitable field.
4) Load up Ruger 10/22
5) Commence firing at useless Video Display Unit,
6) Lament at what we've lost since discontinuance of CRTs.
7) Enjoy yrself immensely at the destruction of Pretender To The Throne...

Vizio's have a lot of main board problems but check the PS first.

On the mainboard there are some little fuses right next where the power enters the board. Check those. I'm not sure if it is this model, but sure sounds right: One of those fuses opens up because it wants to. 2 amp I think. These are surface mount fuses, and about the size of a grain of rice. Probably square cross section and about 1/4 inch long. Another thing I see on Vizio mainboards is failure of the little 3 terminal regulator chips scattered all over the place. If the TV turns on and just sits there not doing anything more, not even turning off it may be one of those. they tend to put out 1.25,1.8, 2.2, 3.3 volts, stuff like that. Good luck

That's the GV47L that is prone to the fuses blowing. On the GV42, I would second the suggestion to look for a bad power supply or mainboard. I have two of this model to look at this week too. I saw them in my queue.

I fixed a set like this once, it was a pair of surface mount fuses that had gone high resistance. Jumpered across them, it's been working fine for the last few years.

ive seen these with failed U22 voltage regulators on the main board, and with failed master/slave inverter boards.

I just adopted that model and replaced the two backlight inverter boards. Funny thing is it has a decent tuner and DX's quite well!

Ok, I got a look at the GV42LHDTV set today... my nephew got the back off just fine, wow what a pile of screws!

My observations:

PS board; no bulging or oozing caps could be seen, fuse near input checked good. I could not find any test points, but the output connector wires labeled "12V" had about 12.02 volts and the those labeled "24 V" had 24.62 Volts. Are there more points that I should check, or is the PS ok?

Main board; There are indeed two small surface mount fuses near a connector...a 3A and a 5A if I read the tiny print correctly. Both checked good (0.2 ohms or less). No bulging or oozing caps on that board either. Looks like perhaps 10 or so surface mount 3 terminal devices... are all of these regulators? Anybody have a diagram of location/output voltages of these devices?

Refined symptoms... Plug in TV, orange "logo shaped" pilot light comes on... turn on, the logo changes to white (perhaps not as bright as usual, but that may be a perception thing because the screen is not lit). No pix/ No sound. Neither the switch nor the remote will turn it off, must unplug to get back to the orange "standby" pilot light.

Thanks in advance for any ideas, how many boxes of .22LRs should I get? :)
jr

check your voltages on all your SMD regulators of the main board. U33 being the first to check.

+1.

IIRC U33 should have 3.3 volts on the large tab. If it's bad you can get these chips from mouser.com for pocket change. (plus s/h of course) Search for ZLDO1117

If the voltage is low you can sub the 3.3 V from a bench supply for test purposes. Expect it to draw the better part of an amp. If you replace the IC be careful not to break the teenie-tiny surface mount resistors near the IC. I like to put a glob of 60/40 solder on the pins first, then remove the solder with solder wic, and this draws away most of that lead-free solder crap they use at the factory. Then pry the pins up gently with a needle while heating with the iron.

Interesting! If the regulated voltage appears at the tab, it should be easy to measure without shorting anything.... I will give it a shot!
thanks,
jr

I went over this evening and measured all of the three terminal regulator devices on the main board that I could find. U33 was a small 16?pin ic, so I did not try to measure it. Here is what I read: u4=3.3v, u5=1.22v, u6=3.3v, u7=1.8v, u8=3.3v, u9=1.8v, u10=1.8v, u16=2.5v, u18=1.5v.

du1(large) =5v, du2=3.3v, du3=2.5v, du4=1.22v.

Any ideas?
Thanks,
jr