Vizio E550VL: Plug In = continuous on/off clicking

[ulsh72]

OK. I'll organize this as simply as possible.

DEVICE: Vizio E550VL, contains an LG LC550WUB-SCA1 display.

PROBLEM: Immediately upon plugging in power cord, the power cycles on/off every 2 seconds. Power on is associated with a distinct click and 'vizio' insignia on front lights up orange. It then immediately cycles off with another click and vizio insignia goes black. The vizio insignia never goes white. The screen never comes on. Time from on to off is perhaps 1/4 second, very quick.

TESTING THUS FAR: No visible component defects noted. No bulging or leaking caps, nor burn marks etc..
Tested Fuses: All test good (will retest for peace of mind ASAP)
Disconnected all cables from Main Board except power cable from PS (labeled connection 1). Issue still recurs.
Disconnecting both power cables from PS to inverter boards (connections 3&4) yields the same on/off behavior, but at a fast rate.
Disconnecting connection 1 on diagram from power supply to main board eliminates cycling, but off course does not allow TV to operate. Upon jumpering 5v pin to PS-ON, the display does NOT turn on, but I am able to measure the rest of the pins at connection 1 as follows:
12v= 11.66v
5v= 5.04v
A,B,C= 0v
Connection 2 (pins are labeled 18v and gnd, cannot see in pic)
18v= 17.98v
NOTE: Upon accidental short between PS-ON and pin A at connection 1, the back light comes on without any noted defects. (I suspect pin A is BL_ON signal from main board?)

Thats as far as I can get because the power cycles too quick to be able to get any readings from the main board. I have a standard digital voltmeter, a little amateur experience diagnosing, tracing, and soldering consumer electronics in the constant chase to save a buck and request any assistance you fine folks may be able to provide. I attached pics to help clarify the above. THANKS!

[budm]

Re: Vizio E550VL: Plug In = continuous on/off clicking

"A,B,C= 0v" OK, the main board is not sending any of the command signals, I do not remember which is which but, they should be PS_ON, BL_ON, DIMMING.
So I would check the fuses if any on the main board, check the voltages of the regulator ICs.

[ulsh72]

Re: Vizio E550VL: Plug In = continuous on/off clicking

Thanks bud, I appreciate your assistance immensely.

I was only able to test A, B, and C with PS_on jumpered to 5v, and the cable (labeled '1') disconnected from the main board, so 0v is normal, right?
That is what is so frustrating, I can't test anything with the main board connected since that is when it flashes on/off and too quick to take any voltages, not to mention the stress on all the components while its doing it.

I'll retest the fuses tonight, but initial testing showed all good.

Is it safe to jumper 5v to A, B, or C to turn on components for testing while the main board is disconnected?

Also, would placing a load on 12v help test the PS? Whats the min/max load I should use for a test load? I have a 72W 12v led strip I can use...

Lastly, I have not been able to find any technical documentation on this tv, although I guess thats pretty normal for vizio. If you have any leads on documentation, that would be helpful as well.

So, in summary of above:
1) Is 0v normal in A,B,C when PS is jumpered on, but main board is disconnected?
2) Is it safe to jumper 5v to A,B,or C to turn on components for testing under load?
3) Can I place a 72W load on the 12v as a test load? If not, what is the safe min/max load for testing?
4) Do you have any documentation?
I have already reviewed and been following the guides on here and in your signature. They are most helpful, but I am severely restricted with having to keep the main board disconnected for testing.

I suspect the main board is the problem, but will go through the steps to rule out the PS, then we can try and figure out how to test the Main Board with it acting the way it is.


Cheers!

"A,B,C= 0v" OK, the main board is not sending any of the command signals, I do not remember which is which but, they should be PS_ON, BL_ON, DIMMING.
So I would check the fuses if any on the main board, check the voltages of the regulator ICs.

[budm]

Re: Vizio E550VL: Plug In = continuous on/off clicking

OK, the board does have PS_ON pin, so A, B, or C are not used for PS_ON. A, B, C are used for the BL_ON and Dimming.
You can force on the power supply using 100~1K resistor between PS_ON and 5VSB, when you do that you should then see the 24V and the 12V at the connector, you can do with out the load just to see if the voltages come up to the value first. You do have 5VSB right ?

[ulsh72]

Re: Vizio E550VL: Plug In = continuous on/off clicking

Yep, that is what I did for the voltage testing as noted. I tested the 5v from 5VSB pin, and used that to jumper to PS_ON to test the above.

When I accidentally shorted 5v to pin A, the backlight came on, so it would appear the 24v supply is fine as well. Does this conclude the PS is good, or do I need to test the 12v under load?

If it sounds like the PS is good, do you have any suggestions on how to begin troubleshooting the main board?

OK, the board does have PS_ON pin, so A, B, or C are not used for PS_ON. A, B, C are used for the BL_ON and Dimming.
You can force on the power supply using 100~1K resistor between PS_ON and 5VSB, when you do that you should then see the 24V and the 12V at the connector.

[budm]

Re: Vizio E550VL: Plug In = continuous on/off clicking

Your power supply is good.
You can start checking the fuses and regulator ICs on the main board next, not sure if this is one of those VIZIO with EEPROM problem or not.

[ulsh72]

Re: Vizio E550VL: Plug In = continuous on/off clicking

I haven't found any reference to this type of issue in correlation with the eepprom issues, but certainly a possibility.
I'll test for continuity on the fuses and ICs with power off.
If that all checks good, could I cut the PS-on wire and jumper it with the main board cable attached? Or is there a big risk of frying the PS if the main board can't cut power to PS-on?

Obviously I'm not familiar if there is auto shutdown protection on the PS sidefor only on the Main Side...

Thanks!

[budm]

Re: Vizio E550VL: Plug In = continuous on/off clicking

You have to cut the PS_ON wire going back to the main board otherwise the line will be forced LO and not allow it to go high when resistor is connected. If the resistor is left in palce, the power supply will be fully on 24/7 and never get turn off even when TV is in standby mode, so it is not a good idea to leave the resistor in place. I have a feeling that with forcing on the power supply, you will have to force on the backlights also, but more likely that the TV is still not working and no pictures on the screen.

[ulsh72]

Re: Vizio E550VL: Plug In = continuous on/off clicking

Ok. If that gets the main board to stay on, at least i'll be able to take voltage readings on ICs and other tests. I can't do any testing on the Main when it's power cycling so fast...
I'll be testing tonight and let you know how I make out!

You have to cut the PS_ON wire going back to the main board otherwise the line will be forced LO and not allow it to go high when resistor is connected. If the resistor is left in palce, the power supply will be fully on 24/7 and never get turn off even when TV is in standby mode, so it is not a good idea to leave the resistor in place. I have a feeling that with forcing on the power supply, you will have to force on the backlights also, but more likely that the TV is still not working and no pictures on the screen.

[budm]

Re: Vizio E550VL: Plug In = continuous on/off clicking

The main board is on all the time because it runs from 5VSTBY, when TV is on, then the main board provides the PS_ON signal to turn on the 12v for the audio amplifiers, and 24V for the backlights inverter.
You should be able to measure the regulators just by having the TV plugged into the outlets, there will be no 12V at this point feeding the main board but that is not to worry right now, no need to force on the power supply. We already know that you have main board problem, just need to find out what the problem is.

[ulsh72]

Re: Vizio E550VL: Plug In = continuous on/off clicking

Yes, but as soon as I plug it in it starts to power cycle when I have the main hooked up. Not when I turn it on, but when I plug it in. So I don't have any way of keeping power on the main to measure anything.
I'm retesting fuses and checking for shorts in ICs now.

[budm]

Re: Vizio E550VL: Plug In = continuous on/off clicking

"Yes, but as soon as I plug it in it starts to power cycle " Monitor the 5VSB to see if it is going up and down, same on the PS_ON pin.

[ulsh72]

Re: Vizio E550VL: Plug In = continuous on/off clicking

Yes, the 5vsb is cycling as it clicks on and off.
Does this mean a probable short in the 5v system on the main board?
I have also found a possibly abnormal reading on U4.
U4: pin 1 & 3 = 1.2 ohm
Pin 1 & 2 = 79.1 ohm
Pin 2 & 3 = 80.4 ohm
And yes,thats ohms, not M-ohms or k-ohms.
Also U4 diode test:
1 to 3 (and vise versa) = 0.00v
1 to 2 (and vise versa) = .036v
2 to 3 (and vise versa) = .036v
Does this sound normal? Looks like its a variable ic, type 1117. These readings are very different than others so far.

[ulsh72]

Re: Vizio E550VL: Plug In = continuous on/off clicking

Notwithstanding my previous response, I think I just realized above that you meant after cutting the PS-on wire but keeping the main connected to the PS, and not jumpering anything. The main will get 5vsb and I can see what happens and hopefully get some voltage readings...doing it now.

[ulsh72]

Re: Vizio E550VL: Plug In = continuous on/off clicking

Ok, same result after cutting PS-on. 5vsb is still cycling.

Notwithstanding my previous response, I think I just realized above that you meant after cutting the PS-on wire but keeping the main connected to the PS, and not jumpering anything. The main will get 5vsb and I can see what happens and hopefully get some voltage readings...doing it now.

[budm]

Re: Vizio E550VL: Plug In = continuous on/off clicking

OK, it can be due to too much load due to bad components on the main board, or the 5VSBY is weak due to bad caps and cannot handle the load.
Let try using simulated load on the 5VSBY using 5 Ohms 5Watts minimum to simulate 1A load and see if it is stable at 5V. You just need to run the power supply by itself with 5 Ohms load.

[ulsh72]

Re: Vizio E550VL: Plug In = continuous on/off clicking

Ok. Use a car dome bulb. I got steady 1.28A draw at 5.01v. No cycling, nice and steady.

[budm]

Re: Vizio E550VL: Plug In = continuous on/off clicking

Good, so the problem is the main board is drawing more than the power supply can handle.
I really do not know the easy way to find which components on the board is drawing too much current since the power supply goes into shutdown/restart mode not long enough to see which component gets hot.

[ulsh72]

Re: Vizio E550VL: Plug In = continuous on/off clicking

Thanks bud!
You got me way further than I could on my own, that's for sure. I'm going to measure the resistors at the U4 IC since its a variable IC to see if I can tell if my readings make sense or not.
I'm also going to grab a can of compressed air and try that trick to try and find the offending component.

Thanks again!

[budm]

Re: Vizio E550VL: Plug In = continuous on/off clicking

Just post the follow-up on what you find.