Vizio SV420XVT1A missing 12v on main board

[bikerbuddy]

Need some help with this main Board I am working on , The TV power on with amber light and stay on , no picture or sound , I jump the power supply with a 1000 ohm resistor and have all the right voltage comes up with main board cable disconnected , but the 12 v that supposed to go into the main Board is not showing up at the fuse on the main board .

I took some reading on the voltage regulators and this is what my findings are

U45
AZ7805ST
adj out in
000 000 000

U16
AZ7805ST
adj out in
000 000 000

U19
0809 ul (1084)
adj out in
1.258 2.057 5.08

U22
G1117 (k218)
adj out in
2.055 3.29 5.13

U17
G1117 (k218)
adj out in
2.079 3.32 5.07

U20
0809 ul 1084
adj out in
.556 1.812 3.31


U21
G1117 k218
adj out in
.001 1.242 2.497

[budm]

Re: Vizio SV420XVT1A missing 12v on main board

'U19
0809 ul (1084)
adj out in
1.258 2.057 5.08"

Vout = 1.25Vref + Vadj
So in your case you have 1.258 @Adj pin so the output should be 1.25Vref +1.258Vadj = 2.50V, you are only getting 2.057V so you need need new regulator.
12V is switched power supply, it will not be present until PS-ON command is sent to the power supply board from the main board.

[bikerbuddy]

Re: Vizio SV420XVT1A missing 12v on main board

Thanks Budm, I looked on line and cannot find this regulator , not even a hint of it ,Is there a substitute I can use . thanks

[dick_barton]

Re: Vizio SV420XVT1A missing 12v on main board

Can you post a picture of' U19, 0809 ul (1084)

[bikerbuddy]

Re: Vizio SV420XVT1A missing 12v on main board

here is a pic of U19 DB.

[bikerbuddy]

Re: Vizio SV420XVT1A missing 12v on main board

here is a pic of U19

[bikerbuddy]

Re: Vizio SV420XVT1A missing 12v on main board

here is a full main board pic

[vinceroger69]

Re: Vizio SV420XVT1A missing 12v on main board

Maybe this?
https://cdn.badcaps-static.com/pdfs/...d543900844.pdf

although on google images the marking at the top is ap maker

[bikerbuddy]

Re: Vizio SV420XVT1A missing 12v on main board

Should i look into 3.3 or adjustable ?

[vinceroger69]

Re: Vizio SV420XVT1A missing 12v on main board

im sure budm will advise the correct replacement as im not sure myself

[budm]

Re: Vizio SV420XVT1A missing 12v on main board

What you have is the Adjustable type, NOT the fixed output type, you can tell by the resistor network connected to the ADJ pin and the Output pin.
So get the Adjustable type.

[Diah]

Re: Vizio SV420XVT1A missing 12v on main board

hold on, you checked PWB with IK R and 12 Volts was Okay. set turn on but no picture and sound. .. did you get the MB out and checked under layer of bad soldering..?

[bikerbuddy]

Re: Vizio SV420XVT1A missing 12v on main board

Yes I went through the under side all looks ok , Thanks you.

[bikerbuddy]

Re: Vizio SV420XVT1A missing 12v on main board

Will order that part and post back later, Thanks to all .

[dick_barton]

Re: Vizio SV420XVT1A missing 12v on main board

Maybe this?
https://cdn.badcaps-static.com/pdfs/...d543900844.pdf

although on google images the marking at the top is ap maker

+1 That's also what I found when I searched and I fairly certain you are correct.

[dick_barton]

Re: Vizio SV420XVT1A missing 12v on main board

Have you checked if you have all the voltages on the power supply. So you have 12V for the main board and 24V for the inverter at the power supply?
You say that the 12V going to the mainboard does not show up at the fuse. Does it show up at the power supply and have you used your ohmeter to do a continuity check (with set off) to make sure the wire connected to the 12V pin at the power supply end actually connects to the mainboard at the fuse?
Have you check the fuse continuity for open circuit?

[budm]

Re: Vizio SV420XVT1A missing 12v on main board

He has to find out if he has PS-ON signal to turn on the 12V/24V, he is not getting the 12V to the main board right now.

[bikerbuddy]

Re: Vizio SV420XVT1A missing 12v on main board

Conformed ps/on voltage is .035 v ,I do have 12v , 24v when I disconnect the main board cables and use jumper on ps/on to 5v .

Any way i have ordered the LM1084 adj from Mouser so we will see what the results will be within a week or so .
Very greateful for all the help .

[bikerbuddy]

Re: Vizio SV420XVT1A missing 12v on main board

Update , Chip has arrived today LM1084 which is a replacement for 0809 UL

Installed it and Did not find any change it is showing In 5.08v, out 2.508V, adj 1.258V ,still cannot get 12V to main board , also did jump the( ps-on to 5v) again to make sure that the P/S is still putting out 12V all voltage on P/S are correct

24V = 24.27v
12v =12.01v
5v = 5.01v
A = .056
B= .023
C = .000

Big chip under the heat sink is getting very hot, hotter than the normal touch .would this be an indication that the chip is toast?

[budm]

Re: Vizio SV420XVT1A missing 12v on main board

Your readings:
24V = 24.27v
12v =12.01v
5v = 5.01v
A = .056
B= .023
C = .000
I am confused, in post one you said you do not have 12VDC at he fuse but right now you do have 12.01V from the the power supply, same for the 24V so it means the main baord is sending the PS-ON to the power supply board to turn on the 12V/24V power supply.
You must have 12v at the both ends of the fuse on the main board at this point.
Right now I see that the main board is not sending the BL-ON or the Dimming signals (A & B) which are routed through the power supply board to get to the inverter board.
BTW, what DCV do you have now at U16, U45?
U45
AZ7805ST
adj out in
000 000 000

U16
AZ7805ST
adj out in
000 000 000
Same as shown above still?