Vizio E321VL Doesn't power on

[AmpWare]

Hello I picked up this TV from a friend broken. He said it was working fine then one day just wouldn't turn on. After looking at a few thread on this and similar sets I ordered a replacement eeprom and swapped it but it didn't improve the operation of the TV.

When you press the power button on the TV or the remote control the orange vizio emblem briefly flashes white then right back to orange. If you hold down the power button it will repeat this same cycle once every couple seconds.

I checked the voltages on the power supply while pressing the power button. The 12v comes up to 12v for only about 1/10th of a second then drops back to 0v. The on signal from the main board pulses the same way. I disconnected the cable from the main board and used a 3.7v battery cell from ground on the power supply to the "Remote ON/OFF" pin. As long as the voltage is applied to the pin the 12v supply comes up to 12.2v and remains steady. The voltage on the large primary side capacitor goes up to 396v also from 167v when the supply is turned off.

After doing a couple checks I decided to connect another lead from the battery to the Backlight ON/OFF pin. This is where things go wrong. The backlights flash on and off at a couple times a second and the 12v output drops between every flash as well. I suspect there may be something going on with the power supply when it's under a load and is why the set will only power very briefly then back down.

If I unplug either or both sets of ccfl bulbs the power supply does the same thing and only small LED near the OZ9977BGN chip flashes. This LED also flashes along with the backlights when they are plugged in.

I'm not all that familiar with troubleshooting these types of power supplies. So I figured I would turn to more seasoned pros for suggestions.

If I can't repair this one I have no problem ordering a replacement power supply but I want to be reasonably sure that it's a wise investment

If more photos or information is needed just let me know and I'll see what I can do.

[multimeter]

Re: Vizio E321VL Doesn't power on

check resistance with respect to cold ground on the output +rails,you should see many kohm's,a few ohms would indicate a short

check output diodes for shorts,there are 2 large ones next to heatsink,shottky? ,remove one leg test with diode setting on meter

test esr of output caps
i need to learn to spell lol.

darned combined inverter/psu's !
im thinking there is a short on one of those rails

[AmpWare]

Re: Vizio E321VL Doesn't power on

I tested the 2 large diodes. They both seem ok. They are feeding the 5.2v standby line anyway. I don't have a ESR meter but I pulled the caps and tested with a 1khz square wave and oscilliscope. According to the scope the larger caps are nearly a dead short at 1khz and the smaller 10uf caps allow a small amount of the 1khz square wave through but it's heavily attenuated. The backlight switching mosfets look like they are supplied power by the large primary cap and are driven by the IC OZ9977BGN through the 2 small transformers T350 and T351. I may try removing the mosfets and test them out of circuit

[AmpWare]

Re: Vizio E321VL Doesn't power on

After following the circuit around a bit I noticed the backlight inverter IC is powered by the same 12v supply that drops to 0v when there is a load present so the backlight circuit may not be the cause and just shutting off cause the power to the PWM is being interrupted

[budm]

Re: Vizio E321VL Doesn't power on

"When you press the power button on the TV or the remote control the orange vizio emblem briefly flashes white then right back to orange. If you hold down the power button it will repeat this same cycle once every couple seconds."
First, verify that the 5VSTBY is steady at 5V.
"The on signal from the main board pulses the same way" That means the main board is not working properly, that can be due to bad STBY power supply or something else on the board is bad.
So check the stby and report what you are getting.
If the 12v also dropping down, check and see if the voltage on the main cap is also going up and down.

[AmpWare]

Re: Vizio E321VL Doesn't power on

First, verify that the 5VSTBY is steady at 5V.

I won't be able to test that till tomorrow morning when I have the whole tv in front of me again. I only have the power supply board to work with currently. The remainder of the TV is at work.

If the 12v also dropping down, check and see if the voltage on the main cap is also going up and down.

The voltage on the main cap rises to almost 400v and stays there if i force the power supply on by supplying 3.7v to the Remote ON pin and the 12v output holds steady at 12.2v. It's not till I either plug it into the mainboard or attempt to turn on the backlight (even with it disconnected from mainboard) that the 12v supply collapses. At that point the voltage on the main cap starts falling back to the "off" value of ~168v.

As far as the mainboard and the pulsing "on" signal is concerned is it possible the mainboard is expecting a stable 12v feed within a certain time after power on and simply powering back down if it doesn't get it?

[budm]

Re: Vizio E321VL Doesn't power on

Once the power supply is getting the steady PS_ON signal, the PFC Voltage booster circuit will kick up the DC voltage to 380~400VDC and it should be steady like that until you remove the PS_ON signal, so if you force on the power supply using 3V battery, that voltage should never drop down to 167VDC. If then you apply the inverter on signal while the PS_ON is still present, the backligts should come on , the PFC voltage should then be able to maintain the voltage, but if it drops down when you force on the backlight, then we need to find out why, and since the PFC IC and the PWM IC for the inverter circuit runs off from the AUX winding of the stby power supply, if the stby is not steady then the 12v, the inverter, the PFC will go crazy. So right now we need to find out if stby is OK or not first, you need to monitor that when the TV malfunction, no need to have the main board connected to the power supply board for now, just use the battery as you are doing.

[AmpWare]

Re: Vizio E321VL Doesn't power on

Once the power supply is getting the steady PS_ON signal, the PFC Voltage booster circuit will kick up the DC voltage to 380~400VDC and it should be steady like that until you remove the PS_ON signal, so if you force on the power supply using 3V battery, that voltage should never drop down to 167VDC. If then you apply the inverter on signal while the PS_ON is still present, the backligts should come on , the PFC voltage should then be able to maintain the voltage, but if it drops down when you force on the backlight, then we need to find out why, and since the PFC IC and the PWM IC for the inverter circuit runs off from the AUX winding of the stby power supply, if the stby is not steady then the 12v, the inverter, the PFC will go crazy. So right now we need to find out if stby is OK or not first, you need to monitor that when the TV malfunction, no need to have the main board connected to the power supply board for now, just use the battery as you are doing.

Is it safe to test without the backlights connected? I tried it once and got a flickering LED that lit up on the back side of the power supply. I assume thats just an indicator showing the backlight circuit is on but i know some backlight circuits aren't well behaved without bulbs connected

[budm]

Re: Vizio E321VL Doesn't power on

You have to have ALL the lamps connected, otherwise open lamp detection circuit will kick in.

[AmpWare]

Re: Vizio E321VL Doesn't power on

Yeah I figured it wouldn't stay on. Some circuits will run a couple seconds or so then power off but I've even had some of the small inverters for laptops emit the magic blue smoke without a bulb attached. I'd rather avoid causing more damage than the set has currently and I don't have any suitable ccfl's laying around to use so I'll probably just pick up tomorrow again at work where I can plug the power supply back into the tv.

I was also thinking.. I have a number of computer power supplies that have pretty beefy 5v and 12v rails. do you think it would be possible to test the main board using that as a replacement voltage source? obviously the backlights wouldn't work but if I could get the set to stay powered on and get an image going I could see with a flashlight it would probably mean the mainboard is working

[budm]

Re: Vizio E321VL Doesn't power on

Yes you can use the external 5V and 12v to power up the stand alone main board.

[AmpWare]

Re: Vizio E321VL Doesn't power on

Alright thanks guys. I'll reply tomorrow once I have a chance to monitor the standby voltage with the powersupply faulting on and off. I'll also give the PC powersupply a shot and see if it will power on the mainboard.

[AmpWare]

Re: Vizio E321VL Doesn't power on

Ok I'm back and have checked the standby voltage output. With the main board disconnected and the power supply forced on the 12v and 5v standby are steady at 12.2 and 5.2v. when I enable the backlight circuit the backlights start flashing on and off and the 12v and 5v standby both fall to nearly 0 and back up to full voltage every second or so roughly.

When the power supply is plugged into the main board and you press the power button the 12v line comes up only for a 10th of a second or so and I can see the standby line sag down to under 5v then the main board powers back off and the 5v standby comes back up to 5.2v. It's possible the standby is is dropping much lower but it's too fast for my meter to detect.

[budm]

Re: Vizio E321VL Doesn't power on

The 5VSTBY should never drop at all. I would concentrate on fixing the 5VSTBY, it can be as simple as star-tup cap C160.
5VSTBY and switched 12V are generated by the same circuit.

[AmpWare]

Re: Vizio E321VL Doesn't power on

The 5VSTBY should never drop at all. I would concentrate on fixing the 5VSTBY, it can be as simple as star-tup cap C160.
5VSTBY and switched 12V are generated by the same circuit.

Yeah I'm going to replace all the cheap brown caps. I have a bunch of donor boards laying around with higher quality nichicon etc.

I did try wiring the 12v and 5v lines up to the main board from a computer power supply and the tv stays on and I can see the shadow of the menu on the lcd so I believe everything else is solid and it's just a power supply thing.

[budm]

Re: Vizio E321VL Doesn't power on

Yes, I think the problem is due to bad 5V power supply.

[AmpWare]

Re: Vizio E321VL Doesn't power on

Well it looks like my adventure ends on this TV. I replaced the startup cap and the bulk filtering for the outputs with better parts but no change so I started working backwards through the circuit from the turn on pin and located a shorted SMT diode. Replaced it and all is well again. It looks like that section of circuit is part of the feedback for the optical isolators.

Thanks for the help. Is much appreciated.

Pics below showing damaged component and powered on set.

[budm]

Re: Vizio E321VL Doesn't power on

Good fix!, so the 5V power supply was the cause of the problem due to shorted diode. The diode looks like it is being fed from main primary supply, you can see bunch of resistor in series then go to one of leg of the 5V SMPS IC?

[AmpWare]

Re: Vizio E321VL Doesn't power on

Good fix!, so the 5V power supply was the cause of the problem due to shorted diode. The diode looks like it is being fed from main primary supply, you can see bunch of resistor in series then go to one of leg of the 5V SMPS IC?

Yeah. it branches off and goes to the IC and a small transitor. Set is working well. Hopefully it stays that way

I actually went over most of the easy to test discrete components my first time around the power supply but I missed that diode. Guess with so many it's easy to lose track and skip some