Vizio SV47OXVT1A Will n0ot power on

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Vizio SV47OXVT1A While watching the TV the sound became very distorted, for a minute or so and then the TV shut down. Now it will not power on. I do not hear a click when I plug it in or push the power button.
I have no voltage out of the power supply except for the 5.5Vdc at the stand by. I checked voltages regulators on the AV main board with the following results
U20 V1, 2.75, VO, 1.25
U15 VI 2.95 VO 1.25
U16 nothing in or out
U21 VI 2.5 VO 1.26
U19 VI 3.77 VO 1.25

I have checked all the fuses and they are good.
In the first photo the middle fuse is good but no voltage to it
The second photo I have no voltage in or out of two regulators
Photo 3 the connector to the power button, channel and volume control, and input
Blk Wire 3.26
Brown 3.8
Red 5.12
Orange 5.12
yellow 1.4
Green 0
Blue 0
Violet 2.2, but only when the power button is pused in and held in
Gray 0
White 3.3

By the syptoms I was first thinking Main AV board but with no power at the outputs of the power supply has me cornfused,,,, does the Main AV board turn on sections of the power supply? All the diodes on the power supply tested good. No bulging caps, dark or burnt spots on the boards.
Main AV board CSD: 3647-0102-0395
Power Supply DPS 379AP A

[retiredcaps]

Re: Vizio SV47OXVT1A Will n0ot power on

I checked voltages regulators on the AV main board with the following results
U20 V1, 2.75, VO, 1.25
U15 VI 2.95 VO 1.25
U16 nothing in or out
U21 VI 2.5 VO 1.26
U19 VI 3.77 VO 1.25

See my sig file below on how to test and report the voltage regulators. Without part numbers, we can't tell if they are good or bad.

BTW, I count at least 7 regulators and 5 fuses on the main board.

By the syptoms I was first thinking Main AV board but with no power at the outputs of the power supply has me cornfused,,,, does the Main AV board turn on sections of the power supply?

The main board is responsible for turning on the secondary power supply outputs via PS_ON pin. It will generally toggle the pin "high" or > 3V.

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Re: Vizio SV47OXVT1A Will n0ot power on

I found 6 regulators am I missing one. All 5 fuses test good with a continuity tester

U20 pcb designation
Line 1 0811KL
Line 2 1084
Pin 1 .558V
pin 2 1.81V
pin 3 3.30V

U15 pcb designation
Line 1 0811KL
line 2 1084
pin1 2.08V
pin2 3.34V
pin3 5.04V

U21 pcb designation
Line 1 K333
line 2 G117
pin 1 .4mv
pin 2 1.25V
pin 3 2.51V

U45 pcb designation
line 1 AZ7805T
line 2 807J48
pin 1 3.9mv
pin 2 .2mv
pin 3 1.7mv

U16 pcb designation
line 1 AZ7805T
line 2 807J48
pin 1 4.2mv
pin 2 0V
pin 3 0V

[retiredcaps]

Re: Vizio SV47OXVT1A Will n0ot power on

I found 6 regulators am I missing one.

I circled 8 in red. There may be more, but with the angle of your photo, I can't tell.

You only reported 5 test results.

All 5 fuses test good with a continuity tester

Early on, I tested fuses with the continuity tester. A fuse tested "good" because my multimeter beeped. Later on, I realized that my multimeter beeped for anything less than 75 ohms. As it turned out, my fuse was 18 ohms and was bad.

A good fuse should measure less than 1.0 ohms. This is how I test it and recommend everyone else tests it. The continuity feature has its uses, but not when it comes to checking a fuse. I have kept that 18 ohm fuse as a reminder to myself.

There is one Mastech multimeter that will beep "continuous" for anything less than 1800 ohms (eighteen hundred).

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Re: Vizio SV47OXVT1A Will n0ot power on

I'll try and get you a better photo in the am. I'll check the others you marked and list them at the same time.
I forgot to list U19
Line 1 0811KL
line 2 1084
pin 1 1.27
pin 2 2.52
pin 3 5.06
Thanks for the help

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Re: Vizio SV47OXVT1A Will n0ot power on

OK finally made it out to the garage, here are the voltages for the other two voltage regulators
U17 pcb designation
line 1 K333
line 2 G1117
pin 1 2.07
pin 2 3.31
pin 3 5.01

U22 pcb designation
line 1 K333
line 2 G1117
pin 1 2.07
pin 2 3.31
pin 3 5.08

Tested all 5 fuses on the AV board for voltage from left to right
F6 5.08 F4 4.98 F1 5.08 F2 0 F5 5.08



I also tested the following
D120 pcb designation Shottky Diodes all out of circuit
line 1 STPS2045CT
line 2 GK10L
line 3 CHN325
Tested it out of circuit and it tested good

D907 pcb designation
line 1 STPS20L60CT
line 2 GK08PVW
line 3 CHN825
Tested out of circuit and tested good

D200 pcb designation
line 1 STPS2045CT
line 2 GK1OL
line 3 CHN325
Tested out of circuit and it tested good

D240B pcb designation
line 1 CQ825
line 2 B20H100G
Tested out of circuit and tested good

D240A pcb designation
line 1 CQ825
line 2 B20h100G
Tested out of circuit and tested good.

Q905 pcb designation
line 1 FQPE
line 2 3N80C
Mossfet I beleive it is leaky, when tested with black lead on drain and red lead on source and touching G&D together. Using an analog meter the needle would go to about center, hold for about 1 sec then fade to 0.

Tested the following transistors in ciruit with a BK 520B they all tested good

Q651 pcb designation
line 1 K3569

Q652 pcb designation
line 1 K3569

Q601 pcb designation
line 1 K3568

Q602 pcb designation
line 1 K3568

Let me know if you need anything else

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Re: Vizio SV47OXVT1A Will n0ot power on

I forgot to add that I also tested all the electrolytic caps on the power supply. I tested in circuit with a blue esr meter and they all seem to be with in specs.

[retiredcaps]

Re: Vizio SV47OXVT1A Will n0ot power on

I have no voltage out of the power supply except for the 5.5Vdc at the stand by. I checked voltages regulators on the AV main board with the following results

Observations so far.

1) So U16 and U45 are both 7805 regulators and both have on input voltage on the main board.

2) I have no idea where they are on the board because I can't read the pcb designations. Thus, the two above could be working properly since they could be for a USB port or something similar. Or they could be responsible for the sound and dying?

3) 5.5V standby seems high to me. In your picture with the power board connectors, it not so clearly says 5VSB. At 5.5V SB, it is running 10% out of spec.

4) Somewhere on the power board connector should be a pin marked PS_ON. This is generated by the main board to tell the power supply to power on the secondary voltages. PS_ON is enabled when voltage is typically > 3V.

5) So what is PS_ON when you press the on/off button?

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Re: Vizio SV47OXVT1A Will n0ot power on

U45 and U16 are the two to the far right on the AV board.
Do you think the mosfet on the power supply is OK.
I added the info below. I'll check the PS_ON in the am

Q905 pcb designation
line 1 FQPE
line 2 3N80C
Mossfet I beleive it is leaky, when tested with black lead on drain and red lead on source and touching G&D together. Using an analog meter the needle would go to about center, hold for about 1 sec then fade to 0.

[retiredcaps]

Re: Vizio SV47OXVT1A Will n0ot power on

Q905 pcb designation
line 1 FQPE
line 2 3N80C
Mossfet I beleive it is leaky, when tested with black lead on drain and red lead on source and touching G&D together. Using an analog meter the needle would go to about center, hold for about 1 sec then fade to 0.

I don't have an analog multimeter at home so I can't comment on how it is supposed to behave. For mosfets, I do a simple test for shorts.

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Re: Vizio SV47OXVT1A Will n0ot power on

Standby is 5.13, PS_ON has 0 volts at all times. The black wire for the PS_ON correlates to the fuse that has no power also. How do you check a mosfet for shorts?

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Re: Vizio SV47OXVT1A Will n0ot power on

where does the PS_ON power originate from, the main board? Does anyone have a troubleshooting guide for this TV. Are there any good troubleshooting books for LCD/Plasma TV's

[retiredcaps]

Re: Vizio SV47OXVT1A Will n0ot power on

Standby is 5.13, PS_ON has 0 volts at all times. The black wire for the PS_ON correlates to the fuse that has no power also. How do you check a mosfet for shorts?

1) PS_ON at 0V means the main board isn't generating it. You might want to check the on/off switch panel to make sure there is voltage present?

2) See section on mosfets.

https://www.badcaps.net/forum/showpo...4&postcount=19

3) Please circle in your diagram which black wire and fuse. Post a close up picture of that area.

[budm]

Re: Vizio SV47OXVT1A Will n0ot power on

Here is the simple explanation how LCD TV works.

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Re: Vizio SV47OXVT1A Will n0ot power on

Thanks, retiredcaps and budm

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Re: Vizio SV47OXVT1A Will n0ot power on

The red pencil is pointing to the fuse that has no power to it. the black wire on the far right goes to the PS_ON pin on the power supply board. Do I have a bad main board?

[retiredcaps]

Re: Vizio SV47OXVT1A Will n0ot power on

Can you retest fuse F2 with just ohms and not continuity?

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Re: Vizio SV47OXVT1A Will n0ot power on

The fuse shows 0.7 ohms, and just for giggles I checked the black wire and it is 0.7 ohms also

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Re: Vizio SV47OXVT1A Will n0ot power on

Am I right in thinking I need to repalce the main board? I found one for about $80.00 but hate to spend the money if I don't have too.

[budm]

Re: Vizio SV47OXVT1A Will n0ot power on

One thing you can try is to feed the PS_ON pin on the main board using 1K resistor from 5VSTBY pin to the PS_ON pin, but you MUST cut or remove PS_ON wire that goes back to the main board due to the transistor that supplies the PS_ON signal on the main board may be stuck on at this moment. If the power supply does kick on and you can see that the TV will function normal, then the problem can be just bad PS_ON signal from the CPU.
See this link: https://www.badcaps.net/forum/showthread.php?t=22309