Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

[MisterD]

I have a 42" Vizio here model SV420M that has a normal vizio logo,that lights up amber color when in standby mode, then the normal white when powered on. has no backlight, black screen and no sound,

I measured voltages on the power supply board connectors and got 5.2 v on +5VSB.... PSON had .27V when powered on and 0V when powered off...On/Off Inverter had .05 volts when powered off and 2.16V when tv powered on. 12V is not present, I checked both fuses on the main board both are good, one on the left has 5.2 V, one on the right has 0V on both ends, resistance on fuses showed continuity so neither one is open.I think the fuse on the right is on the 12V supply but for some reason I'm not getting the 12Volts.

I'm thinking a mainboard problem instead of the PS board, also no voltage on regulator U6 ( checked it for shorts was okay in circuit ) as someone else had with the same model TV, Any help suggestions of what to check next is greatly appreciated. Thanks

[budm]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Yep, you do have main board problem.
Please list all the voltage readings of all the regulators.
You are not getting the 12V because the PS_ON is not present, >2V = ON, <1V = OFF.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Voltage Regulator readings.
U2 118DF 1117L
Pins
1. 2.04 V
2. 3.28 V
3. 5.23 V

U6 118DF 1117L
1. 0 V
2. 0 V
3. 0 V

U7 118DF 1117L
1. 2.05 V
2. 3.3 V
3. 5.11 V

U8 MC 7805 CT RAF 824G
1. 0 V
2. 0 V
3. .02 V

U4 8DF 1117L
1. 0 V
2. 1.25 V
3. 3.3 V

U3 1084 0849HL
1. 2.05 V
2. 3.31 V
3. 5.11 V
U5 same as U3 same numbers on regulator and same voltage readings.

U9 1084 0849HL
1. .56 V
2. not connected
3. 3.30 V

Hi Bud!!! Should I try to apply 2 V DC to PSON to see if it will turn on the 12 Volts? would i possibly then get backlight, picture and sound? or would doing that possibly damage other parts due to a shorted component? please reply back, help needed. Thanks!

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

I still have these 2 different type 1117 LDO Regulators from a previous order from Digikey, I used 2 to fix a Vizio 42" LCD made in 2007 that i fixed in 2012, does anyone know if either of these will work on this SV420M???? Here's some pictures of the 2 different packages they came in.

I was thinking of maybe replacing U6 with one of these, not sure if that's the problem or if these are still the same type of regulator.

I remember now that one of these that i ordered is the adjustable regulator type and the other is the fixed.

[budm]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Some of those regulator will not have voltage feeding them until the 12V is present, I.E. U8 5V regulator.
You can disconnect the wire that goes to the PS_ON pin of the power supply first use 500~1K resistor between the PS_ON pin on the power supply and the 5VDTBY to force on the power supply to give you the needed 12V for the main, then check the voltages again on U6 and U8.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Thanks Bud, I disconnected wire from mainboard to PS_ON and used a 1k resistor as you said to, plugged in and turned on with remote control and I now have a normal picture and sound.

I can still change volume levels but some functions don't work I.E. can't change channels, no menu function but can still change video input, also I don't think there's an on screen display but hard to see with a little mirror on a garage workbench close to the wall.

Here's the readings on U6 12.20V in on pin 3, 8.13V out on pin 2 and 6.88V on pin 1
readings now on U8 are 12.20V In, 5.03V Out and .01V on middle pin.

What can I do next? Thanks for the help so far, you are Great as always..

[budm]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

U8 is 5V regulator so it is OK (middle pin is the ground pin for the 78XX series regulator).
U6 is also OK (1.25V ref + 6.88V on pin 1 = 8.13V on pin 2).
So the regulators are OK but the main board is not fully functioning, there is not much I can suggest but replace the main board unless you can actually see damaged components on the board.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

I followed the wire from PSON back to the mainboard, found a small resistor and checked voltage there and it was .27v and .25v at other side of resistor, I couldn't tell where the circuit trace went from there.

I may pull the mainboard off and check and resolder connections in that area, other than that I'm not sure if a component I.E. IC chip,transistor or diode may have failed. Hard to troubleshoot without a schematic giving voltages at locations. This mainboard 3642-0692-0150 is expensive and out of stock by some sellers. Thanks again Bud.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

leaving the TV powered on for awhile with the jumper and 1k resistor from 5V STBY to PS_ON results in a very hot heat sink on the main board processor, checked with a laser thermometer and was at 125 degrees fahrenheit, I think these normally run a lot cooler when functioning normally, I think the problem is that the processor being a BGA has some bad or shorted connections, I don't have much luck doing a re-flow. anyone got any suggestions on possibly how to re-flow the BGA processor??? anyone?? Thanks.

[mscserbia]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

See reflow process on youtube.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

After programming the TV, Channel scan etc. all functions work now and it has a good picture and sound. BUT!!! I still have to have the 1k resistor hooked up as follows. disconnect PS_ON wire from main board, connect 1k resistor from 5V STBY to PS_ON pin on power supply connector.

TV will the power on and off and work normally, what would happen if I just leave it like this??? I'm still not sure about the main processor on the main board, the heat sink on it feels pretty hot after the set is on awhile, I have a cheap laser thermometer that showed it was 125 degrees Fahrenheit, I don't know if that is too hot, does anyone know???

[budm]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

You just have to unplug the TV or use outlet strip to kill the power to the TV when it is not in used.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

The TV turns on and off now with the remote or power button and appears to function normally even though the PS_ON wire is disconnected from the main board and I have the 1k resistor from 5V STBY to PS_ON. but would probably be best to unplug anyway.

Also bud m , do you think that it is normal for the processor on the main board to get so hot??? Thanks.

[budm]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

125F is about 51c so it is not that hot hot but I have no idea what it should be. Right now you are actually just turning the BACKLIGHTS on and OFF but not the power supply, the power supply is fully on since it is being forced on.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Okay, This main board is really hard to find, someone else posted information about sending their board in for repair and return to Modus Link out of Bloomington Indiana, right now they are having a sale so I can send my main board in and get it repaired for $78, they pay the shipping back to me but I believe I have to pay to ship to them, which would only be about $6.00 USPS priority mail with tracking and $50 insurance, I would probably pay extra to increase the insurance. have you heard of this company? Thanks again bud m

[budm]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

I have heard of the them but never use them before. So that is the flat fee. I would ask them if that will fix the heat problem also.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

All of the phone numbers I have found so far have been disconnected but their website is up and running, I saw a couple bad reviews so I'm not sure yet, maybe I will just wait it out and try to find a board or see what happens if the set is used like this, or try to troubleshoot the reason I'm not getting the correct PS_ON voltage from the main board.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Voltage regulator U7 on the main board has zero volts when the tv is off but even with the PS_ON wire unhooked from the Power Suppy I can still turn the tv on and off (power supply not on then) watching the vizio logo light go from amber to white, when it's white the regulator U7 has 5.11 v on input and zero volts when tv turned off, I was thinking of soldering a wire from U7 Input, putting the 1K resistor in between it and the PS_ON.

This would then give me the needed 3V for PS_ON when I turn on the TV and then Zero Volts when I turn it off, would the 1k resistor be isolating the connection from the input voltage at the regulator to PS_ON? if I did that and it worked the Power Supply would then be off every time I turn the TV off. Should I try this or would it damage the Main Board or Power Supply? bud m what do you think?

[budm]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Using 1K is very light load (only about 5mA max) current draw, you should be OK. The question will be is that the PS_ON must be present BEFORE the BL_ON is present since you need to have the power supply to be steady first before turning on the inverter circuits which draws lots of current that can cause the power supply to sag a little due to in rush, that is why there is slight delayed turn on of the BL_ON signal. You need to monitor the BL_ON LINE and the Input to U7 to see which one goes HIGH first.

[MisterD]

Re: Vizio 42" LCD Model SV420M, Black Screen no sound vizio Logo normal

Okay, I ran the wire from U7 In and thru 1k Resistor to PS_ON, here are some pictures and voltage readings at PS_ON, .45v when set is off and 2.89 when set is on, everything appears to be working normally with the exception of the vizio logo white light flickers sometimes but the 2.89v to PS_ON is stable, I didn't monitor the BL_ON LINE and the Input to U7 to see which one goes HIGH first, will do so later. So I guess this would be called a bypass repair.