Another Vizio SV421XVT that won't power up

[Pauls72]

I have a 42" Visio SVT421XVT that suddenly won't power up a few months ago. The orange logo is on the front is lit and never changes to white.

I've used an Ohm meter, Capacitance meter and ESR meter to check all the can type cap's. I have replaced a number of cap's that where bad or questionable on both the power inverter and main board. Still no difference. From what I'm seeing, I believe the problem is on the main board.

These are the chip part numbers and the current voltage readings. All these readings are with the power on/off button being held on.

Connectors on the power inverter board:
INV ON/OFF = 0.00v
DIM2 = 0.00v
DIM1 = 0.00v
12V = 1.18v
ST/+5V = 5.18v
18V = 0.19v


Main Board - p/n 3642-0722-0150 (5E)
U1
49530M or 49536M (I can't tell if the last digit is a 0 or 6)
924034
pin 5 5.11v
pin 6 5.11v
pin 7 5.11v
pin 8 5.11v

U2
L163
G9117
pin 1 2.07v
pin 2 3.31v
pin 3 5.12v

U3
L312
G1084
pin 1 2.07v
pin 2 3.31v
pin 3 5.11v

U4
L163
G9117
pin 1 0.02v
pin 2 1.261v
pin 3 3.318v

U5
L312
G1084
pin 1 2.06v
pin 2 3.31v
pin 3 5.08v

U6
L163
G9117
pin 1 0.00v
pin 2 0.00v
pin 3 0.01v

U7
L163
G9117
pin 1 2.07v
pin 2 3.31v
pin 3 5.11v

U8
AZ7805T-E1
920019
pin 1 0.01v
pin 2 0.02v
pin 3 0.01v

U9
L312
G1084
pin 1 0.57v
pin 2 1.83v
pin 3 3.31v

U10
L204
G5627
pin 1 5.07v
pin 2 0.80v
pin 3 0.01v
pin 4 0.81v
pin 5 3.90v
pin 6 0.00v
pin 7 0.74v
pin 8 5.08v


I looked at the Vizio DC-DC trouble shouting workflow and it is basically useless.
I'm open to any suggestions.of where to go next.

Thanks,
Paul

[budm]

Re: Another Vizio SV421XVT that won't power up

The LDO voltages look OK, the one with 0V (U8, U6) input is due to the power supply is not turn on by the main board. You need to look at the PS_ON pin from the main to see if it is present.
Main board right now is not sending PS_ON, BL_ON (INV ON/OFF), or DIM signals.

[johnboy1313]

Re: Another Vizio SV421XVT that won't power up

Check for any surface mount fuses on the main board as well.

[Pauls72]

Re: Another Vizio SV421XVT that won't power up

Been trying to work on the TV, but it's been sporadically.
The fuses are all OK.

I looked at this other thread which was basically the same problem as me and did some of the same troubleshooting.
https://www.badcaps.net/forum/showth...v421xvt&page=3

Leaving the Main Board (pin1)
INV ON/OFF = 1.07v (off) - 1.19v (on)

At the output pin of the regulators
_____off____on
Q1 = 5.00v 0.00v
Q2 = 0.00v 0.70v
Q5 = 0.00v 3.30v
Q7 = 0.67v 0.72v after about 3 seconds it goes to 0.03v
Q8 = 0.00v 3.21v

R1 = 1.07v (off) - 1.19v (on) - other end of R1 = 1.09V (off) - 1.22v (on)
R11 = 1.09V (off) - 1.22v (on) - other end of R1 = 0.00V always

I also replace these (2) 220uf @ 25V cap's.



I pulled pin 1 (INV ON/OFF) from the connector.
I took a 330 ohm and jumper-ed the INV ON/OFF wire to the output of Q5 through the resistor.

The power supply comes on and so does the display.

So at this point in time, on the main board R1 which normally feeds the INV ON/OFF pin.
R1 = 1.09v (off) - 1.21v (on) the INV ON/OFF
A couple hundredths of a volt higher with no load.

I guess this is some progress.

[Pauls72]

Re: Another Vizio SV421XVT that won't power up

Well I screwed up, I was looking at U5 instead of Q5

At the output pin of the regulators
_____off____on
Q1 = 5.00v 0.00v
Q2 = 0.00v 0.70v
U5 = 0.00v 3.30v
Q7 = 0.67v 0.72v after about 3 seconds it goes to 0.03v
Q8 = 0.00v 3.21v

I pulled the board and then took the one cap off and took a lot of pictures so I could accurately trace what goes where. I even metered out from this via pass through to all the transistors and could not find a direct connect to any of them. Not only the ones nearby, I went to every transistor on the board.

The INV ON/OFF signal goes through this via pass through.


The INV ON/OFF signal then makes quite a trip around the bottom of the board and goes through this via pass through.


Which unfortunately comes up through the board under this heat sink, approximately here.


Not very promising.

[Pauls72]

Re: Another Vizio SV421XVT that won't power up

So I ended up taking the output of regulator U5 and running it through a 330 ohm resistor to the wire I pulled for the INV ON/OFF signal going back to the power supply. About 95% of the TV works, there are only 2 things that don't:

1) The Power/Standby indicator always shows amber like it's in standby. No big deal.
2) The 3 HDMI ports on the back of the TV are dead. However the 4th HDMI port on the side works great.

The Tuner, all the AV and component jacks work just fine and all of the functionality of the TV works just fine.

So for now I put the TV back together and am living with it. Some day I'll buy a Main board and put the pin back in the connector. Main boards for this set seem hard to come by, most places are out of stock and then they have a hefty core charge too.

[budm]

Re: Another Vizio SV421XVT that won't power up

Yep, use it until it dies then the price of the board may come down in price by then, good job for not dumping the TV into the garbage yet.

[football0062]

Re: Another Vizio SV421XVT that won't power up

Just my recent experience with this i wanted to share. i was having the same issue with my set(wont turn on, vizio logo stay amber) took my measurments and noticed my STBY with is the power on signal was 230mv when turned on and 14mv when off. obviously 240mv isnt enough to turn the power supply on. traced back to R1 in the main board. 3.3k resistor. measured good but when in circuit it failed. 3.3v on one side and 240mv on the other. replaced R1 and unit fired right up!!

CHECK R1