Vizio M321i-A2 power board

[vikingTv]

so have the panel in the subject, no standby juice at all on pin 1. power button does nothing (obviously with no standby). (i tested with cable attached and not attached)

so I'm thinking bad power board. The fuse checks out fine (darn it) and i have power on the far side of it from the power source. Looking around the power boards for these things are far more expensive then what I would put in this TV, 60ish dollars.

I got this panel for free, so I can monkey with it and if it doesn't work out I'm not really out anything. So I am keen to try my first venture into board level repair on this board. But, I'm a complete noob to this. I've done plenty of swap out components to bring various electronics to life, I have fixed a power supply of a PS4 by replacing a fuse and I've fixed an ice maker by soldering in a new switch, but this is another level above what i've done, but would like to learn.

So I guess what I'm asking is how do I proceed with my multi-meter to figure out what component is bad thx!

[nomoresonys]

Re: Vizio M321i-A2 power board

With power cord unplugged, unhook all connectors from powerboard, plug in power cord, see if you at least have your 5 volt standby voltage if not you need to find out why, power cord is good? Do a check of all your diodes, youtube is your friend if you need help on procedure, one on diodes: https://www.youtube.com/watch?v=hTFwiG_mosM

[vikingTv]

Re: Vizio M321i-A2 power board

thx. so tested the diodes on the board (I had already tested for 5v standby with all connectors unplugged).

The diode circled is allowing volts in both directions. Now. I did not, obviously, de-solder the diode from the board to test it, testing it on the board is ok i think?

The other diodes check out fine, fuse has continuity. So i guess next step is to figure out the replacement diode and solder that in and see what i got.

[nomoresonys]

Re: Vizio M321i-A2 power board

It's prolly bad, testing it out of circuit will confirm for sure.

[budm]

Re: Vizio M321i-A2 power board

thx. so tested the diodes on the board (I had already tested for 5v standby with all connectors unplugged).

The diode circled is allowing volts in both directions. Now. I did not, obviously, de-solder the diode from the board to test it, testing it on the board is ok i think?

The other diodes check out fine, fuse has continuity. So i guess next step is to figure out the replacement diode and solder that in and see what i got.

It is showing low Ohms reading?

[vikingTv]

Re: Vizio M321i-A2 power board

It is showing low Ohms reading?

I put the multimeter on the diode setting.

In the direction the current is supposed to flow I get a 0.27 V reading.

In the opposite direction I get a reading of 0.7 V reading to start, what I noticed this time is if i leave the leads on there it starts to climb up and eventually reads .0L which is what is should read if I understand this right. All the other diodes when I do a reading in the opposite direction of the flow immediately read .0L (open loop) but this one always starts at around .7

So do i need to go back to multi-meter school?

as an aside I did a continuity test and as I expected I get continuity the direction the flow is supposed to go, but no continuity the opposite direction.

edit...
against the direction of the flow I get an OHM reading of ~39 M, in the flow direction i get 8.7K.
the other diodes all read open loop testing resistance against the flow.

[budm]

Re: Vizio M321i-A2 power board

Take it off the board and set the meter to Ohm mode (start at 200 Ohms scale) and test it in both directions.
That D202 is for 5V.
https://www.shopjimmy.com/vizio-56-0...pply-unit.htm#

[vikingTv]

Re: Vizio M321i-A2 power board

Take it off the board and set the meter to Ohm mode (start at 200 Ohms scale) and test it in both directions.
That D202 is for 5V.
https://www.shopjimmy.com/vizio-56-0...pply-unit.htm#

I know it's been a while. but been busy...

finally got around to de-soldering this diode out. once it's out of the board the diode test works like it should, current one direction. So i guess this particular diode is not really testable in board. As if I put it back in the board it shows current in both directions once again on the diode test.

I tried the OHM test with the diode off the board as well, my meter just auto selects the level and can't change it. but against the flow the resistance ia 17 M. with the flow it's 47 K.

So guess this diode is not that problem. I'll solder it back in. I do know I do NOT get 5V on pin 1. after i solder it back in I'll do a reading on all the pins with the power connected.

[dick_barton]

Re: Vizio M321i-A2 power board

What dc voltage do you have between the two legs of the 82uF 450V capacitor.