Vizio VP422 won't turn on.

[Malachi]

Re: Vizio VP422 won't turn on.

I made a mistake dick. The meter doesn't beep.
Q8101 and Q8102 are sd20n60.
Q8201 and Q8202 are FDA 18N50.

[dick_barton]

Re: Vizio VP422 won't turn on.

Q8101 and Q8102 should measure diode between Pins 2 & 3 (Drain/Source)
Q8201 and Q8202 should measure diode between Pins 2 & 3 (Drain/Source)

[budm]

Re: Vizio VP422 won't turn on.

https://www.badcaps.net/forum/attach...0&d=1462483285

The power devices AFTER the fuse F8201 are the Q8201, Q8202, U8301, and U8001 (this one is after another fuse (F8002). So for the fuse to blow there must be one of those device that has very low resistance reading.

Q8101 and Q8102 are for the PFC Booster circuit and they are BEFORE the fuse F8201, if Q8101 and Q8102 are shorted then it would have blown the Main AC fuse F8001.

[dick_barton]

Re: Vizio VP422 won't turn on.

Hi budm,
It's a problem without a schematic to check on and other than trying to trace the circuits from the pictures, which to be honest I don't fancy doing because of the time involved.

Lets see what reading are posted for Q8201, Q8202

[budm]

Re: Vizio VP422 won't turn on.

The tracing that I made in the picture is close enough to show how that fuse feed the circuit. i just hope that it is not OP measurement error and causing us to chase our tails and get to be over 100 posts like the other thread.
BTW, those two POWER MOSFETS circuit section that drive power transformer T8201 for the VS, VG supply are not turned on until it gets the command ON signal.

[dick_barton]

Re: Vizio VP422 won't turn on.

lol. I hope not too. Got there in the end though.

[dick_barton]

Re: Vizio VP422 won't turn on.

BTW, those two POWER MOSFETS circuit section that drive power transformer T8201 are not turned on until it gets the command ON signal.

Still puzzled why the diode check is negative. It wouldn't explain the fuse blowing because as you said there's a low reistance somehere in the circuit. 4 Amps is not such a small fuse.

[budm]

Re: Vizio VP422 won't turn on.

He needs to use the lamp in series with the power supply board so it will show if he still has shorts on the board or not. I still wonder what happen since it was not one of the original problem.

[Malachi]

Re: Vizio VP422 won't turn on.

Dick, they all read OL. All the Q parts.

[budm]

Re: Vizio VP422 won't turn on.

See if you have low resistance between point 'A' and point 'B'.

[Malachi]

Re: Vizio VP422 won't turn on.

If I have to rig up the lamp jig that I saw you guys talking about, that's too much for me.

[budm]

Re: Vizio VP422 won't turn on.

See post 70.

[dick_barton]

Re: Vizio VP422 won't turn on.

Check between all 3 legs of the device for a low reading on Q8201, Q8202.
Pin1- 2 , Pin 1-3, Pin 2-3
Then reverse your meter leads and repeat.

[Malachi]

Re: Vizio VP422 won't turn on.

See if you have low resistance between point 'A' and point 'B'.

0.5ohm.

To be honest, now I'm not sure if the second fuse blew open when the psu was disconnected from everything.
When I get the fuses in, I'll put one in and then power up the psu while it is out of the TV.

[Malachi]

Re: Vizio VP422 won't turn on.

Check between all 3 legs of the device for a low reading on Q8201, Q8202.
Pin1- 2 , Pin 1-3, Pin 2-3
Then reverse your meter leads and repeat.

A reading with the meter set to diode mode? Or on resistance?

[budm]

Re: Vizio VP422 won't turn on.

0.5ohm.

To be honest, now I'm not sure if the second fuse blew open when the psu was disconnected from everything.
When I get the fuses in, I'll put one in and then power up the psu while it is out of the TV.

You have shorts AFTER the fuse for sure for you to get 0.50 Ohm reading between 'A' and 'B'.

[Malachi]

Re: Vizio VP422 won't turn on.

You have shorts AFTER the fuse for sure for you to get 0.50 Ohm reading between 'A' and 'B'.

I know that. It's so short, I took the fuse out there is nothing in there. Lol.

[Malachi]

Re: Vizio VP422 won't turn on.

The lowest reading on the diodes is 99 ohms. Most of the readings were in the K range and higher.

[budm]

Re: Vizio VP422 won't turn on.

So you have 4 devices Two MOSFETs, and two IC that are being power AFTER the fuse, so it is a matter of isolating those parts off the board, there are also snubber cap in parallel with each MOSFET, but if they are bad then you would have seen < 1 Ohm between S and D pin by now.

[dick_barton]

Re: Vizio VP422 won't turn on.

What are the IC part number number that budm identified earlier so I can look them up.