Vizio P502UI-B1E, quick question about PS_on

[DXseekerMO]

Hello all, I just got a Vizio P502ui-B1E. When I toggle the power on switch and monitor its connector at the main board I get a voltage drop from 2.9 to .3 or so. When I monitor PS_on at the output on the main board and toggle the switch it remains 2.9v.

This sounds like the PS_on circuit on the main board is malfunctioning?

I also have no stand-by light.

Thanks everyone.

[budm]

Re: Vizio P502UI-B1E, quick question about PS_on

"When I toggle the power on switch and monitor its connector at the main board I get a voltage drop from 2.9 to .3 or so."
Need clarification as to which connector and which pins and the pin names that you are getting the readings.

If the PS-ON is stuck high (>2V = main power supplies ON, <1V = main power supplies OFF).
Since the Standby Voltage must be present otherwise you will not see that stuck PS-ON Voltage, but as you indicated that there is no standby lights at all, that indicate problem with the main board.
If part of the power supply board is OK, then you should see about 380 ~400 VDC when measured right between the two legs of the main filter cap on the HOT side.
It will also help if you up load good clear pictures of the whole back side of the TV showing all your boards.

There are many threads about this model also:
https://www.badcaps.net/forum/search...rchid=10394861

[DXseekerMO]

Re: Vizio P502UI-B1E, quick question about PS_on

Sorry about that budm, the one that the voltage toggles on is the on button input to the main board. The stuck voltage is the output to the power supply.

Where is the standby light on that TV anyways?

[budm]

Re: Vizio P502UI-B1E, quick question about PS_on

It is actually power indicator light that lights up white when TV is turned on, if I remember correctly it is on the bottom left edge of the TV bezel, the key point right now is that the PS-ON Voltage should toggle high and low when you turn TV ON and OFF.

[DXseekerMO]

Re: Vizio P502UI-B1E, quick question about PS_on

It sure doesn't on the output side to the power board. That means its a main board issue? Corrupted EEPROM perhaps?

[DXseekerMO]

Re: Vizio P502UI-B1E, quick question about PS_on

Ok so I took pictures of the board arrangement and the boards, plus made an interesting observation:

Like I said when I toggle the switch at the switch connector (input) on the main board I see 2.9 open and .3 closed. When I go to the other side of the connector I have the same. When I trace away from the connector there's a surface mounted component, not sure if its a cap or fuse.

On the connector side of this component I have toggling voltage, but on the other side I have nothing, zero regardless of whether the switch is open or closed.

This looks like a good reason for no PS_on toggle to the power supply. My theory: if this component is open there's no way the processor "sees" the power button is being pressed?

[budm]

Re: Vizio P502UI-B1E, quick question about PS_on

Ok so I took pictures of the board arrangement and the boards, plus made an interesting observation:

Like I said when I toggle the switch at the switch connector (input) on the main board I see 2.9 open and .3 closed. When I go to the other side of the connector I have the same. When I trace away from the connector there's a surface mounted component, not sure if its a cap or fuse.

On the connector side of this component I have toggling voltage, but on the other side I have nothing, zero regardless of whether the switch is open or closed.

This looks like a good reason for no PS_on toggle to the power supply. My theory: if this component is open there's no way the processor "sees" the power button is being pressed?

So you hit the 'INPUT BUTTON' and the Voltage on the switch connector change state, but what happen when you hit the 'POWER BUTTON' does the Voltage at the switch connector change state? How about if you use remote to turn TV on and OFF, does PS-ON change state? At this point you have the problem on the main board some where that causes the PS-ON to stuck high and if the power supply board is OK then you should have all the Voltages at the power supply output connectors.

[DXseekerMO]

Re: Vizio P502UI-B1E, quick question about PS_on

Okay let me try to explain. On the annotated picture, the brown wire with the arrow comes direct from the power button. The black wire right next to it also comes direct from the power button.

When I press the power button voltage drops from 2.9 to .3. on the brown wire, connector side.

When I check the pin on the other side of the connector associated with the brown wire, on the circuit board side it also goes from 2.9 to .3 when I press the power button.

When I trace that circuit I come to a fuse or ceramic? cap, surface mounted. On the input side (towards the connector) the voltage goes from 2.9 to .3 when I press the power button.

When I go to the other side of this fuse or cap I have zero volts at all times, power button pressed or not.

This surface mounted component appears open and is on the circuit directly to the brown wire that leads to the power button.

It does the same with the remote.

[budm]

Re: Vizio P502UI-B1E, quick question about PS_on

Well that is capacitor, one end is connect to GND this why you get 0V, so that is not the problem.
So when you see 0 V on one end of the part, then you should find out if one end is connected to GND or not by using simple Ohm meter to find out.
Since the power switch signal does toggle then there is no problem with the power switch, it also means the switch isn't stuck. The signal from the switch is fed to the controller which then will send out a bunch of control signals such as PS-ON , BL-ON , DIM, T-CON on, etc. So at this point I do not understand what you are trying to do.

[DXseekerMO]

Re: Vizio P502UI-B1E, quick question about PS_on

So at this point I do not understand what you are trying to do.

I hate to say it budm, but I'm pretty sure that makes two of us.

I think I'm doing a really lousy job explaining this. Let me try this:

When I press the power button voltage drops from 2.9 to .3. on the brown wire, connector side. When I release the button it jumps back up to 2.9

When I check the pin on the other side of the connector associated with the brown wire, on the circuit board side it also goes from 2.9 to .3 when I press the power button. When I release the button it jumps back up to 2.9

The PS_on wire from the main board to the power board remains at 2.9v power switch open or closed.

Perhaps the easiest thing to say is something on the main board is bad?

[budm]

Re: Vizio P502UI-B1E, quick question about PS_on

"Perhaps the easiest thing to say is something on the main board is bad?" YES! that is about the 4th times.
As I already explain: the power switch is doing its job by sending the LOW signal to the micro controller but at this point the output of micro controller is not changing state when its input is getting the signal from power switch.
PS-ON signal pin is not connected DIRECTLY to the power switch! All the switches are connected to the input pins of the micro controller.

[DXseekerMO]

Re: Vizio P502UI-B1E, quick question about PS_on

You have the patience of a saint. I appreciate it budm.

[DXseekerMO]

Re: Vizio P502UI-B1E, quick question about PS_on

Well I was going to heat up the eeprom in this TV to see if it would boot, but I found this:

[budm]

Re: Vizio P502UI-B1E, quick question about PS_on

It looks like some trying to remove the chip but gave up on it.
BTW, where did you get this TV from?

[DXseekerMO]

Re: Vizio P502UI-B1E, quick question about PS_on

I saw a video, think it was from norcal715 on YT....that was the first thing I thought of when I saw that.

I actually removed that solder, made sure the pins were still soldered on, powered it up and noticed a change of state. The power light actually came on and the TV responded when I hit the power button. The light flashed, stayed on for a few seconds then trailed off to a trickle, very dimly lit. The power button then became unresponsive until I unplugged and hard reset the TV.

I also tried heating up the eeprom with no change in the light sequence above.

This TV was sourced through an ad.