Vizio E420-A0 fails to sustain power

[lkvee]

Acquired the "non-working" TV from someone who got a replacement TV through an extended warranty.

TV will shutdown eventually on its own - longest "session" was less than one minute. In some instances, the TV never generates a backlighted Vizio logo and its power LED immediately starts to fade after going full bright white.

I can't replicate the exact behavior with regards to duration of the power-on state. Sometimes the TV fails to turn on. Sometimes its power LED will light and then fade. Other times the TV will behave as expected before generating the "No Signal" box and powering down with backlighting from power-on to sudden shutdown.

Someone else tested the voltages going from the power board to the video board, and I remember him saying the 5V standby was present. We did not test voltages going from the power board to the LCD strips.

Caps have not popped and at least one is by Chemicon.

We tested the power cord and got continuity even when twisting the cord (at both ends).

Friend who tested voltages from power board to video board was thinking there's something wrong with the keyboard controller board (POWER button, change input, menu navigation, etc.). He thought a bad power board would at least give consistent behavior, even if that behavior didn't lead to a working TV.

Just discovered bad EEPROMS, too:

https://www.badcaps.net/forum/showthread.php?t=47930

Just not sure how to test such an EEPROM:

https://www.amazon.com/Vizio-E420-A0...E420-A0+EEPROM

What else should I examine and diagnose further?

[dskall]

Re: Vizio E420-A0 fails to sustain power

Need voltages from connector that goes from power supply board to main board. Will need pin#- PIN DESCRIPTION -Pin voltage in standby-Pin voltage when pushing power button and picture of connector on power supply board.
Format:
Pin# - Pin Description - Pin Voltage standby - Pin voltage power on
1 - XXXXXXX - XXv - XXXv
2 - XXXXXXX - XXXv - XXXv
3 - XXXXXXX - XXXv - XXXv
4 - etc.
Also voltage across main capacitor

[lkvee]

Re: Vizio E420-A0 fails to sustain power

Just replaced the power board, but still replicated the original symptoms. Here are the readings for the replacement power board going to the main board.

Here's what I got on Standby:

Pin 12 NC Zero Volts
Pin 11 PWM2 Zero Volts
Pin 10 PWM1 Zero Volts
Pin 09 B/L ON/OFF Zero Volts
Pin 08 REMOTE ON/OFF Zero Volts
Pin 07 12V Zero Volts
Pin 06 12V Zero Volts
Pin 05 GND Zero Volts
Pin 04 GND Zero Volts
Pin 03 GND Zero Volts
Pin 02 +5.2Vsb 5.16V
Pin 01 +5.2Vsb 5.16V

Main Capacitor 166V

Here's what I got when the TV was turned on:

Pin 12 NC Zero Volts
Pin 11 PWM2 1.87 Volts
Pin 10 PWM1 sometimes 3.35 Volts, sometimes 1.87 Volts
Pin 09 B/L ON/OFF 3.3 Volts
Pin 08 REMOTE ON/OFF 3.3 Volts
Pin 07 12V 11.89 Volts
Pin 06 12V 11.89 Volts
Pin 05 GND Zero Volts
Pin 04 GND Zero Volts
Pin 03 GND Zero Volts
Pin 02 +5.2Vsb 5.16V
Pin 01 +5.2Vsb 5.16V

Main Capacitor 303V

The only other behavior I noticed was the LED power light. I need to hold down the power button to see the light turn on to half-brightness, dim gradually, and then go to full intensity as the backlighting activated.

I also heard one or two beeps right before the power cut out.

Still not sure how to interpret these findings.

[budm]

Re: Vizio E420-A0 fails to sustain power

"Main Capacitor 303V" That is not right at all.
Are you checking right between the two legs of the cap? That Voltage should be between 380~400VDC range. if that is done correctly then we need to look into that PFC Voltage booster section next.

[lkvee]

Re: Vizio E420-A0 fails to sustain power

I unplugged the TV.
I shorted the leads.
I put alligator clips on the leads and measured DC voltage.

3V unplugged
166V standby

Yes, 303V power-on

[dskall]

Re: Vizio E420-A0 fails to sustain power

Budm can correct me if I have right board and ic. On back of board you need to check resistance of R133a,b and c for ic120

[budm]

Re: Vizio E420-A0 fails to sustain power

What is the DC Voltage rating of that main filter cap C120?
Vizio 0500-0605-0300 (3BS0333912GP) Power Supply/LED Board
http://www.shopjimmy.com/vizio-0500-...led-board.htm#

Pictures provided by shopjimmy.

[budm]

Re: Vizio E420-A0 fails to sustain power

Budm can correct me if I have right board and ic. On back of board you need to check resistance of R133a,b and c for ic120

They look to be for the feedback network to control the PFC Boosted output Voltage.

[lkvee]

Re: Vizio E420-A0 fails to sustain power

TV's not accessible ATM, buuuuuut, my experience with the meter's a bit limited. When I test IC120, am I looking for continuity, current, orrrr ... capacitance?

Will get specs on the main capacitor (voltage and capacitance specs are obstructed by placement and glue).

Would this entire thread change direction if I got the same voltages from the original board? The readings up above were from a replacement board from eBay. Willing to consider the idea that both boards are bad.

[lkvee]

Re: Vizio E420-A0 fails to sustain power

Budm can correct me if I have right board and ic. On back of board you need to check resistance of R133a,b and c for ic120

Best I could do was check resistance for R133a, b, & c, as well as resistance between pins on IC120. Given my eyesight at the time, I couldn't find anything officially indicating Pin 1 (like a notch or a recessed hole). For this post, I am designating the lower left-hand pin as Pin 1 and the lower right-hand pin as Pin 5 if you're facing IC120 with R128 on your left and C125 on your right.

I tested while the power board didn't not get power, because I had to disconnect the power between the board and the LED's to expose the underside. I'm also assuming resistance is same regardless of polarity.

Pin 1 to 2 gives 114.1 kΩ
Pin 1 to 3 gives 164.1 kΩ
Pin 1 to 4 gives 172.0 kΩ
Pin 1 to 5 gives 129.0 kΩ
Pin 1 to 6 gives 3.31 MΩ
Pin 1 to 7 gives 3.71 MΩ
Pin 1 to 8 gives 106.2 kΩ

Pin 2 to 3 gives 9.70 kΩ
Pin 2 to 4 gives 77.6 kΩ
Pin 2 to 5 gives 34.3 kΩ
Pin 2 to 6 gives 3.2 MΩ
Pin 2 to 7 gives 3.62 MΩ
Pin 2 to 8 gives 9.8 kΩ

Pin 3 to 4 gives 68.0 kΩ
Pin 3 to 5 gives 24.64 kΩ
Pin 3 to 6 gives 16.6 MΩ
Pin 3 to 7 gives 17.83 MΩ
Pin 3 to 8 gives 105.0 Ω

Pin 4 to 5 gives 92.6 kΩ
Pin 4 to 6 gives 16.8 MΩ
Pin 4 to 7 gives 17.96 MΩ
Pin 4 to 8 gives 68 kΩ

Pin 5 to 6 gives 16.68 MΩ
Pin 5 to 7 gives 17.88 MΩ
Pin 5 to 8 gives 24.73 kΩ

Pin 6 to 7 gives 6.45 MΩ
Pin 6 to 8 gives 3.19 MΩ

Pin 7 to 8 gives 17.75 MΩ

R133a, R133b, and R133c have "1004" stamped on top.

R133a gives 0.658 MΩ
R133b gives 0.678 MΩ
R133c gives 0.660 MΩ

Looks like the main cap's specs feature 400V and probably 120 uF or some iteration (220, 320, 420, etc.). I was able to replicate the original condition despite physically damaging the cap. Wondering if I should still replace it.

[cliff_hootarski]

Re: Vizio E420-A0 fails to sustain power

I believe the white dot lower right denotes pin 1.

[dskall]

Re: Vizio E420-A0 fails to sustain power

So R133a gives 0.658 MΩ, R133b gives 0.678 MΩ, R133c gives 0.660 MΩ are suppose to be 1mohm resistors. You will need to replace them. You can replace with regular 1/4watt but do not replace all three with only one or two.

[lkvee]

Re: Vizio E420-A0 fails to sustain power

So R133a gives 0.658 MΩ, R133b gives 0.678 MΩ, R133c gives 0.660 MΩ are suppose to be 1mohm resistors. You will need to replace them. You can replace with regular 1/4watt but do not replace all three with only one or two.

This is encouraging news. Can't exactly tell whether R133a, b, and c, are 1206 or another size. I wanted to measure with digital calipers, but I noticed red ... adhesive? ... obstructing the calipers.

If I'm reading the last post correctly, the recommended course of action is to replace all three resistors. Replacing only one or two is not recommended.

[dskall]

Re: Vizio E420-A0 fails to sustain power

You can use regular leaded 1/4w 1mohm resistors. Because of the high voltage going through them they use more to lower voltage across each

[lkvee]

Re: Vizio E420-A0 fails to sustain power

Got a strip of new resistors. Desoldered one and tested it out of circuit.

I got 1 MOhm.

I resoldered the same resistor back in circuit and got the original ~667 Ohm reading.

Not sure what to examine this time