Vizio VW37 Power Supply PSON working but no 12v or 24v output

[PlainBill]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

I can't help feel that you are barking up the wrong tree except for the fact I saw a similar problem in another thread.

In a good design the difference between 3.184 and 3.3 volts on a control line is insignificant. It's a sad fact that there are marginal designs. I assisted on one case (no resolution stated) where a voltage difference of about this much WAS significant. I would be interested in what the PS_ON input circuit at the power supply is. Have you tested the actual 'turn on' point?

PlainBill

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

I mean, I agree with the idea that it is weird for a voltage difference that small to be causing any problems; the relatively close-to-normal PSON voltage is one of the reasons I spent so much time looking at the power supply board in the beginning - because I just assumed that PSON was working fine.

Still, externally driving (with a pair of AA batteries) PSON high results in the power supply board turning on and creating a steady 12 and 24 volt output. Could there be any other possible explanation for this behavior other than a slightly incorrect PSON voltage that is just a fraction of a voltage too small?

[tom66]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

Okay, as far as I understand it:
- power button pressed
- PSON rises to ~3.18V
- rails do not switch on properly

but:
- external power applied to PSON
- rails are fine

But have you tried synchronising the pressing of the power button with applying power to PSON? If you use that PSON switch arrangement again, with the battery pack, it may be possible to press them at the same time.

If it still doesn't work; maybe the low PSON is a sign of a bad LDO for the 3.3V on the motherboard? Maybe the 3.3V is actually fine (3.184V is still in tolerance for most 3.3V devices, although out of tolerance for a typical 1-2% tolerance reg) but it's noisy, due to a failed cap or LDO? Some types of LDO can fail in odd ways, becoming noisy. If you can trace where this mystery 3.184V is coming from, you might find a dodgy LDO. And maybe, just maybe, the PSU's logic doesn't like this noisy signal.

Can you borrow a scope to test this noisy 3.3V idea?

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

I have some updates.

I tried sweeping the board for connectivity of the mystery hole using the setup shown in the pictures. I spent 20 minutes dragging the copper brush back and forth across the board, but had no luck. Not a single beep was given.

The next thing I wanted to see was the behavior of PWM_DIM and BL ON/OFF when PSON was artificially driven high with a pair of AA batteries. I had on multiple previous occasions been able to get the power supply to output a steady 12v and 24v by externally applying power to PSON. This time however it would not work. I did notice some behavior that I think I had read about before, while I was initially looking for a solution to this problem.

When holding down the Power On button on the side of the TV for a few seconds, the power supply would switch on and correctly output the 12 and 24 volts, but would only stay on for a few seconds before dropping again.

I took some measurements from BL ON/OFF:
While TV was off BL ON/OFF=.321v
With TV "on" (3.16 volts PSON, but no 24/12v rails) the BL ON/OFF= .051v.
With TV "on" (few seconds of working rails) BL ON/OFF = .020

For the PWM_DIM:
TV OFF = .330 v
TV "on" (no 12/24v) = 2.121
TV "on" (few seconds of working rails) = .120

I am not sure if the behavior of the PWM_DIM and BL ON/OFF is needed, now that we know that holding the power button on for a few seconds will produce the correct output. Does anyone know what is causing this behavior?

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

More updates:

I was able to externally trigger the power supply to turn on again. The reason I was unable to get it working during the last test was because I had the tv turned on as well. So I just did some more tests.

I am not sure why it took me so long to think to try this test, but with the power board disconnected from everything except the mains (I unplugged the jumper cable from the main board and the two jumper cables from the inverter board), I am able to externally apply a 3.3v source (AA batteries) and have the power board work correctly (proper 12 and 24 volt turn on).

So the power board existing as a single "entity" is able to be turned on and function correctly with a pair of AA batteries triggering PSON. I am tempted to say that this shows that the issue does not reside on the power board, but I feel like that definitive of an answer would be too easy. I feel like without an actual current draw it is impossible to say that the power supply is 100% fine.

When the main board and the inverter board were connected and the tv was turned "on", the AA batteries no longer worked at artificially turning on the power supply.

If I held down the power on button for a few seconds, the power supply would click on and make the same "correctly operating" sound for a few seconds while outputting the correct 12 and 24 volts. After 1 or 2 seconds the voltage would drop back down to around 1-2 volts. During the initial power on time the back-light would flash briefly for a fraction of a second.

Any ideas?

[tom66]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

Can you try turning it on without the inverter, and then without the main board, and see if it comes on with either?

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

With just the inverter plugged in I can externally trigger the PSON to go high, and the power supply will correctly do the 12 and 24 volts. With just the main board I can also externally trigger the PSON to go high, unless I also hit the power on button on the TV. If the tv is turned "on", then externally triggering PSON does nothing and the power supply board does not output the correct voltages.

The back light does not go on when it is just the inverter board plugged in, but I think that may be because the board needs some sort of signal from the main board to turn on the backlight.

[tom66]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

With just the inverter plugged in I can externally trigger the PSON to go high, and the power supply will correctly do the 12 and 24 volts. With just the main board I can also externally trigger the PSON to go high, unless I also hit the power on button on the TV. If the tv is turned "on", then externally triggering PSON does nothing and the power supply board does not output the correct voltages.

The back light does not go on when it is just the inverter board plugged in, but I think that may be because the board needs some sort of signal from the main board to turn on the backlight.

Have you tried synchronously applying 3.3V to the PSON pin whilst trying to turn the TV on through normal means?

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

I have, but it has not worked, possibly for a number of reasons. One is that when I turn the power on using the tv power switch, the power supply jumps to and falls from 12/24 volts almost instantaneously. I have tried syncing up the pushing of the power button and the application of the external 3.3 volts to this, but have had no luck.

The other technique I have tried is to hold the power on button down for a 3-4 seconds. After a few seconds (it seems like the exact length of time will vary a bit) the power supply will click on correctly and output the 12 and 24 volts for a few seconds (a bit longer than the instantaneous jump and fall that occurs when the power supply button is just pressed normally). I have tried to sync up my application of the external 3.3v with the exact moment when the power supply clicks on (while holding the tv power on button) but this has yielded no results.

If I knew what signal the BL_ON/OFF line should be receiving I could also try and power that externally, but since I don't know what it should be at I am at a loss for what to test/try next.

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

Does anyone know what holding down the power button does? It is probably the next place I should look to troubleshoot.

[tom66]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

Does anyone know what holding down the power button does? It is probably the next place I should look to troubleshoot.

Probably brings one of the KEY lines on the button board down.

[romeromichael]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

I am very late to the discussion and new to badcaps. However, I am having the same issue and have read through the thread, using AA batteries I got PSON to fire up voltage 12v/24v. However, there is nothing coming off the mainboard side to the PSON. Now troubleshooting mainboard but the thread just abruptly ended. Did anyone post the end result? What was happening on the mainboard ultimately? Thanks

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

I am very late to the discussion and new to badcaps. However, I am having the same issue and have read through the thread, using AA batteries I got PSON to fire up voltage 12v/24v. However, there is nothing coming off the mainboard side to the PSON. Now troubleshooting mainboard but the thread just abruptly ended. Did anyone post the end result? What was happening on the mainboard ultimately? Thanks

This is still an ongoing thread; the first post was December 15th 2011 and the latest was just a couple of days before your posting. I wouldn't really say it abruptly ended. It has mostly been a slow process of me posting new updates when I think to check something new, or when someone has given me advice on what I should try/check/post results of.

Have you read through this entirety of this thread? Are you experiencing the same issues as me? If that is the case then it would give me a bit of hope for eventually solving this problem. The various paths this entire trouble-shooting process has lead me on made me think my issue was unique (ex: a freak static spark fried some random component somewhere). If you are experiencing similar problems, maybe our symptoms have the same root cause.

I am going to try a few more things on my TV when I get the chance (within a couple of days), and will report back with the results.

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

A question for any experts on this thread:

I have taken three measurements for the values of lines A and B connecting the power supply board to the mainboard. Line B is pin 13, which the datasheet says is the BL_ON/OFF line, and line A is the PWM_DIM.

I have just re-tested these values and matched them to the A and B lines connecting the power board to the inverter board and they are the same, so the A and B lines from the main board to the power board are directly connected to the A and B lines from the power board to the inverter board.

It would seem as though the power board is mostly just a pass-through for the A and B signals from the main board to the inverter board, although there may be some reason for the power board to be aware of these values. I have not traced out the A and B lines on the power board yet.

It seems as though the A and B are not affected at all by the PSON line voltage, which would make sense; however, when turning the board on by the main ON/OFF switch on the side then the values on the B line (BL_ON/OFF) go low (.323 to .017), the values on the A line go high from .33 to 2.122

Any ideas from anyone?

The values given are both for the inverter board lines A and B and the main board lines A and B.

With just the standby voltage:
Line B = .333v and Line A = .33v

With a PSON being supplied by AA batteries:
Line B = .323 and Line A = .332v

With the main switch on the board being on:
Line B = .17 and Line A = 2.122v

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

Ok another really interesting development:

When the PSON line is disconnected from the power board, it correctly and quickly rises to 3.33 volts when the main board is turned on. It remains at 3.33 volts steadily for as long as the main board is turned on.

Does this mean that whatever is lowering the voltage is on the power supply board side. Could it be doing it as a safety issue, or is the voltage possibly leaking somewhere?

[PlainBill]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

Ok another really interesting development:

When the PSON line is disconnected from the power board, it correctly and quickly rises to 3.33 volts when the main board is turned on. It remains at 3.33 volts steadily for as long as the main board is turned on.

Does this mean that whatever is lowering the voltage is on the power supply board side. Could it be doing it as a safety issue, or is the voltage possibly leaking somewhere?

It's time to trace the PSON signal on the power supply. It should go a transistor (BJT or FET), which then drives the emitter on the opto-isolator.
as I mentioned earlier I have seen one case where the PSON voltage coming from the main board was not high enough to turn on the transistor. In your case, the voltage out of the main board is high enough, as you noted, something is dragging it down.

PlainBill

[budm]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

What happen when you run the power supply and force it on unsing external supply but have two 12v bulbs (1157) hooked up in series to handle 24vdc. The lamp should stay on, the 24vdc may have sensed overload so it goes into shutdown due to short circuits in the inverter board.
http://s807.photobucket.com/albums/y...%20SV470XVT1A/

When you use the external source to trigger the PS_ON line, you have to disconnect the lead that goes back to the Main board since the transistor that keeps the PS_ON low will be on.

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

It's time to trace the PSON signal on the power supply. It should go a transistor (BJT or FET), which then drives the emitter on the opto-isolator.
as I mentioned earlier I have seen one case where the PSON voltage coming from the main board was not high enough to turn on the transistor. In your case, the voltage out of the main board is high enough, as you noted, something is dragging it down.

I have traced out PSON to the opto-couplers, and attached a traced out picture. It is probably pretty useless in its current form, but I figured I would attach it anyway just in case someone recognized something that I should instantly check.

I am working on drawing a schematic of it, either by hand or using orcad cadence.

In the picture the PSON line comes in from the left and is show in red. The dark purple connections everywhere are the ground.

It sorta looks like the PSON line goes through two transistors, and then to the light blue line on the middle/right top.

What happen when you run the power supply and force it on unsing external supply but have two 12v bulbs (1157) hooked up in series to handle 24vdc. The lamp should stay on, the 24vdc may have sensed overload so it goes into shutdown due to short circuits in the inverter board.
http://s807.photobucket.com/albums/y...%20SV470XVT1A/

When you use the external source to trigger the PS_ON line, you have to disconnect the lead that goes back to the Main board since the transistor that keeps the PS_ON low will be on.

I will try and find some 12 volt bulbs to check that out. I have yet to look at the inverter board, but would not be surprised if my problem rested on it. Where would the safety shutdown circuitry that would detect an overload be? Would it be on the power board or on the main board?

[Tetranitrate]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

Further modified the picture a bit to account for a 0 ohm resistor, so the circuit has some more ground.

**Now with 20% more ground!**

[tom66]

Re: Vizio VW37 Power Supply PSON working but no 12v or 24v output

Likely, only one of those optocouplers is for sending a PSON signal. Do all the optocouplers face the same way, or different ways?