vizio 42 gv421 no picture/sound

[budm]

Re: vizio 42 gv421 no picture/sound

Picture of the regulators?
This is the way to figure out if the adjustable regulator is good or not:
Notes: we are looking at the regulator with the Big tab up (the big tab is tied internally to the center pin).
Adjustable regulator will have two resistors attached to it, one resistor (Rfb) is between pin1 and pin2, another resistor (Rg) is between pin1 and ground. Pin3 is an input pin.
The voltage between the Adjust pin (left pin) and the center pin (Pin2, output) will always be 1.25V +/- 2% (this is the precision voltage reference), if it is not, it is bad.
To figure out what the output voltage should be: measure the voltage between pin 1 and ground and add 1.25V to that number, that is the output voltage on pin 2 but you have to make sure you do have 1.25 between pin 1 and 2 as noted above

1117 series LDO from DIGIKEY:

SOT-223-3 style casing:

Adjustable:
http://www.digikey.com/product-detai...SCT-ND/1967218
http://www.digikey.com/product-detai...44-1-ND/586244

1.2V Fixed:
http://www.digikey.com/product-detai...40-1-ND/725525
http://www.digikey.com/product-detai...5-1-ND/1865519 1.2A

1.5V Fixed:
http://www.digikey.com/product-detai...SCT-ND/2121241 1A
http://www.digikey.com/product-detai...8-1-ND/1883983 950Ma
http://www.digikey.com/product-detai...26-1-ND/586226 1.2A

1.8V Fixed:
http://www.digikey.com/product-detai...SCT-ND/1967216

2.5V Fixed:
http://www.digikey.com/product-detai...SCT-ND/2121243 1A
http://www.digikey.com/product-detai...9-1-ND/1883984 950mA

3.3V Fixed:
http://www.digikey.com/product-detai...OSCT-ND/660708
http://www.digikey.com/product-detai...SCT-ND/3462387 1.1A

http://www.digikey.com/product-detai...28-1-ND/586228 1.2A

5V Fixed:
http://www.digikey.com/product-detai...SCT-ND/1967217
http://www.digikey.com/product-detai...7-1-ND/1865475

[TimT]

Re: vizio 42 gv421 no picture/sound

thank you! And thanks for the parts list! I will test them again when I get off work and post a picture.r

[TimT]

Re: vizio 42 gv421 no picture/sound

I tested the regulators. the values are in the pictures. still taking this all in

[tom66]

Re: vizio 42 gv421 no picture/sound

OK, something is not right with all regulators in the 3rd pic.

U7 output should be at least 1.25V more than adjust, but is 0.91V with adjust at 0.01V. Input is 1.95V.

U9 has a low input of just 1.95V (may be OK). It is 1.5V type, for some reason different from the rest. It's only got 1.08V on the output, so something is wrong, but there's no way it can manage that output with just 0.45V input-output drop (it's typically minimum 1V for these regulators.)

Other "U" (unknown) is taking the 5.91V and regulating it down to 1.95V... which powers the other two regulators. This is where the fault must be; the adjust-output difference is just 0.7V. I'll bet that other U is U33? It should be 3.3V, I think.

Note -- you don't need to test both the centre pin and tab pin as they are electrically common (i.e. the same.)

[TimT]

Re: vizio 42 gv421 no picture/sound

the " unknown " regulator has CE19 below the chip. cant be seen in the picture. this low voltage " 1.20 " is causing the other chips U7 & U9 to have low voltage?. I tried searching Digikey for the regulators " amc117 " search came up blank. did this yesterday before you provided the links. thank you! i might as well order the fuse to. can i just " stack " the new fuse on the old one and soder it?

[tom66]

Re: vizio 42 gv421 no picture/sound

Yes, you can stack the fuse, I generally like to put them next to the old fuse and solder across. For such a large fuse though, it's not too difficult to remove it, just apply solder to each end, heat alternately and apply a little pressure, it'll scoot right off.

The bad regulator is giving 1.95V out instead of 3.3V. Funny, on Vizios, the 3.3V regulator always seems to drop to about 2V. I have no idea why, but it is a common defect. The part code is AMC1117 but you should replace it with one of these Budm linked to:

Adjustable:
http://www.digikey.com/product-detai...SCT-ND/1967218
http://www.digikey.com/product-detai...44-1-ND/586244

Consider my last post my train of thought... Only the last regulator is failed.

[TimT]

Re: vizio 42 gv421 no picture/sound

so the regulator U9 is bad? or U9 and U7?. THE unknown /CE19 has 1.20 on bottom pin. should this be around 2.0?

[tom66]

Re: vizio 42 gv421 no picture/sound

The unknown "U" regulator is bad - the rightmost one in 3rd image.

The middle (OUTPUT) pin measures 1.95V, it should measure about 3.3V.
The ADJUST pin, when working, is 1.25V below the OUTPUT, so about 2V when working.

The other two regulators are OK. They are not working because the input voltage is 1.95V, instead of 3.3V. The same 1.95V supply is generated by the unknown regulator and fed into the other two to generate two other voltages.

[TimT]

Re: vizio 42 gv421 no picture/sound

I will buy the new regulator and fuse and post back when I get it installed. I will be hanging around here a lot :-) I go to the auction every Thursday they usually have a few TVs. so I decided to buy a few and see if I can fix them up. the last one I bought was a samsung 6000 Series LED Smart TV 55 inch. it has a cracked screen but for 10 dollars I thought the parts would be worth it. this is been a learning experience so far! hopefully 1 day I'll be able to help somebody else out here. thanks everyone!

[TimT]

Re: vizio 42 gv421 no picture/sound

I would like to thank everyone that help me with this TV! I received the parts needed to repair it and Solder the 3 amp fuse on the mainboard. the regulator was very difficult to remove! it would seem the soldering iron wouldn't heat up enough to loosen the pins... I use a dremel to remove most of the chip..lol it worked

then I was able to remove the old regulator. I really did a bad job of soldering it back! I thought it would be a miracle if it worked
but I'm happy to say that it did work and it's working just fine. so big thanks to everyone that helped!! Tom66..thank you!! budm thank you