Vizio GV42LFHDTV10A no pic, no sound, wont shut off

[myjeepsbigger]

Just as the title says, no picture but backlight is working, no sound and the TV won't shut off with the power button or remote.

I have replaced the power supply and mainboard with one I purchased from TVpartsguy.com....however on further inspection I found that the mainboard is not the correct part number. Symptoms did not change at all with these "new" parts installed. I also tried my original mainboard with just the new power supply installed. Same. I seem to be getting all the correct voltages to the mainboard. So I moved on to checking the U33 regulator that I've read about here. It's reading 1.08, 1.87, 4.94 respectively on 1,2,and 3....which would indicate a problem. So just for kicks, I installed the new "wrong" board into it for a second time and measured the U33 on it....and voltages were very similar to my original board. (Also I've looked over all caps on both boards and cannot see any that are obviously damaged/bulged/leaking).

I've already ordered a few new regulators from digikey, because at this point I don't feel like I have much to lose by swapping them out.....but I'm hoping someone can shed a little more light on this for me. Should I be looking at something else or does it seem like I'm on the right track? I'm definitely no electronics repairman, but I have been able to stumble through a few repairs (like the control board on my Hobart welder!).

Any input would be appreciated.

[myjeepsbigger]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

Other voltages I forgot to include:
1 2 3
U2 1.87 3.14 4.96
U7 0 0.82 1.87
U8 1.87 3.14 4.96
U9 0 0.99 1.86
U33 1.08 1.87 4.94

As far as I can tell from what I've read here, only U2 and U8 look ok...but I'm really new at this. It concerns me that my input voltages on U7 and U9 seem to be really low compared to the others. Makes me think my problem is elsewhere. ????

[retiredcaps]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

but I'm really new at this.

Voltage regulators are what people call "jellybean" parts and quite common on many boards.

They usually have a part number like AL1117-33 where the suffix (-33) denotes the output voltage. So in this example, the output should be 3.3V DC. Most voltage regulators have a 1% specification. That is, the 3.3V DC should be

3.3 x 0.99 = 3.267V DC
or
3.3 x 1.01 = 3.333V DC

Anything above or below those values indicates that the voltage regulator is bad.

So for your case, look at all the part numbers and it will tell you what the output voltage should be. If you can't tell, list them all here and we can help verify.

[retiredcaps]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

I forgot to mention that "common" output voltages are 3.3V, 2.5V, and 1.8V DC.

[myjeepsbigger]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

Got the parts today, ordered 4 in case I had multiples failing....but I only needed one! Replaced the U33 and it's working like new again!

Now hopefully I can get them to take back the mainboard that didn't work....

[ke1122]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

I have the exact same TV with the exact same problem. What was the part number for the voltage regulators you ordered from DigiKey.com? I was about to order a new main board and power board from VizParts.com, but I found your post and thought I could save a lot of money by replacing the regulators (after I check the voltages of course).

Thanks,
William

[myjeepsbigger]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

It was from another thread here, but I can't find it now....and I don't have my invoice in front of me. Search for Vizio threads here, I'm sure that's were I got it.

[ke1122]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

I finally got around to testing some voltages and here's what I found:

U2, U7, U8, U9, U33

All had the 1st readout of a positive, 2nd readout of 0, and the 3rd readout of negative.

I also tested P7, pins 2, 3, 4 and 10, 11, 12. I don't remember the exact readouts, but they weren't 12v and 5v, respectively. They weren't even close.

Then I tested some of the connections on the boards to the left and right of the mainboard. Sorry, I didn't jot down the connection numbers, but they all had readings of around 17.5-18.5v, or 1.5v and around 5v. They were all consistent.

With this info I'm guessing the Mainboard is the problem. Power seems to be getting to (and flowing through) the boards to the left and right, but not to all of the tested connections on the mainboard. I'm also going to get a new LVDS cable while I'm at it (this connects to J7).

Unless anyone has any other ideas? I'm definitely open to suggestions since the mainboard cost about $180 plus shipping.

[daimoku]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

U2, U7, U8, U9, U33

All had the 1st readout of a positive, 2nd readout of 0, and the 3rd readout of negative.

What were the the actual readings?

[retiredcaps]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

I finally got around to testing some voltages and here's what I found:

U2, U7, U8, U9, U33

All had the 1st readout of a positive, 2nd readout of 0, and the 3rd readout of negative.

You may not be testing the voltage regulators properly. A negative readout suggests you are using the wrong ground.

See PlainBill explain what and how to test a voltage regulator at

https://www.badcaps.net/forum/showpo...1&postcount=23

[ke1122]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

Sure enough, I wasn't testing them properly. So much for thinking I knew what I was doing.

I'm going to retest now.

[ke1122]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

Ok, here are the properly taken readouts:

U2: 2.76 3.51 5.56
U7: 0.03 1.29 2.82
U8: 2.88 4.85 5.57
U9: 0.00 1.43 2.76
U33: 1.71 2.90 9.3-9.7

I should note that the U2 reading was steady at those numbers. All other regulators were moving targets (+/- .05). U33 input was all over the place (it even dipped down to 8.9), which is why I put a range.

[retiredcaps]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

U2: 2.76 3.51 5.56
U7: 0.03 1.29 2.82
U8: 2.88 4.85 5.57
U9: 0.00 1.43 2.76
U33: 1.71 2.90 9.3-9.7

Post the part numbers of each voltage regulator. Without them, we cannot tell if the voltages are correct or not.

Just by looking at the numbers themselves, I would say all the regulators are "off". This is assuming your multimeter is working properly. Do you have a fresh or new battery in the multimeter?

[daimoku]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

U2: 2.76 3.51 5.56
U7: 0.03 1.29 2.82
U8: 2.88 4.85 5.57
U9: 0.00 1.43 2.76
U33: 1.71 2.90 9.3-9.7

FYI...the proper output readings are:
U2: 3.3V
U7: 1.28V
U8: 3.3V
U9: 1.5V
U33: 3.3V

U8 & U33 appear suspect

[daimoku]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

Forgot to add that these are AMC1117 adjustable output regulators in the SOT-223 package.

[ke1122]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

Forgot to add that these are AMC1117 adjustable output regulators in the SOT-223 package.

According to the Service Manual:

U2: POWER MOS IRF7316TRPBF SMD 8PIN LF
U7: IC AP1117E18LA LF SOT-223
U8: IC AP1117E33LA LF SOT-223
U9: IC AP1117E18LA LF SOT-223
U33: IC SWITCH PI5C3257QE QSOP 16PIN LF

U2 and U33 are both 3 pin, like U7-9. Not sure why the part description says 8 and 16 pin.

This is assuming your multimeter is working properly. Do you have a fresh or new battery in the multimeter?

The batteries are not new, but I've had it for maybe 5 years and rarely used it. It has a low battery indicator, which is not lit. It is a Radioshack 15-range multimeter, part# 22-810.

[retiredcaps]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

The batteries are not new, but I've had it for maybe 5 years and rarely used it. It has a low battery indicator, which is not lit. It is a Radioshack 15-range multimeter, part# 22-810.

A non fresh battery can cause erratic readings. Straight from the 22-810 manual (note the wording "or the meter does not measure accurately") ...



"When low battery appears on the display or the
meter does not measure accurately, re-
place the battery. If the battery power is
extremely low, low battery does not appear."

I suggest replacing the battery with a new one and taking new measurements. You would not be the first to get inaccurate readings on a weak battery on this forum.

[Scenic]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

my DMM measured a AA battery as 6.1 V once because of a semi-dead battery. no sign of the battery symbol on the display yet.. so much for that..

[ke1122]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

I just tested a brand new AA Energizer battery and it read 1.61V. I tested 2 used AA Energizers and they read 1.36V and 0.51V. Should I still get a new battery in the multimeter?

[ke1122]

Re: Vizio GV42LFHDTV10A no pic, no sound, wont shut off

With a +/- 0.8% allowable variance in DCV according to the manual, I'm gonna say yes since 1.61 is ~8% higher than 1.5.

DC VOLTS
(2–20–200–500 V) .......... ± 0.8% of full scale,
± 1 in last digit