Vizio TV E470VL SMPS Flucuation Output Voltage

[nomoresonys]

Images there, some of yours look cracked, a little flux makes the solder flow in nicely: https://www.google.com/search?source...h=708&dpr=1.25

[R_J]

I read which parts you changed and had another look at the pictures.
After another look at your board, I think I found the problem, U201 is in backwards.

[dholley]

Good Morning RJ, I certainly could have installed it backwards. I installed AP431 to replace KIA431, I'm not for positive, but it appears the pins out are opposite and that is why it is installed in the opposite direction. I'm attaching pictures of the pins out for each, will you have a look and see if I indeed installed it backwards?

[R_J]

I still think it's backwards. The AP431S is showing the pin configuration looking from the TOP. I'm sure the original is ok

[dholley]

Ok, I will change it. Thank you.

[dholley]

RJ, i changed the orientation of 431, picture attached. There is approximately one volt higher on the 5 volt output, it used to be around 4 volts flucuation it is now approximately 5.25 flucuating. VCC is flucating between 9 and 11 volts, approximately.

[R_J]

What voltage do you have on the standby pin4 of cn1? if it is around 5v, ground it, if it is around 0~1 volt connect a about a 1k resistor between standby and 5 volts. See if this turns on the power supply

[dholley]

0 volts standby

Connected a 1 k resistor between standby and 5 volts, measured 12 volt output, output fluctuated greatly between 1.45 volts and 11 volts, approximately

[R_J]

I would check the voltage across the main filter when you force the power supply on, That voltage should go from 165vdc to around 185vdc
Another voltage to check is the VCC on the ic, it needs to come up to around 15v and stay there.

There should be a zener diode across the optocoupler on the primary side, check that is isn't shorted, also check the voltage on pin4 of the ic, maybe it's voltage will indicate something.

It is possible the ic is damaged and won't come out of burst mode.

[dholley]

Things seem strange

I forced the power supply on, I took measurements on the big caps and for a moment they measured around 234, then out of range, a second later 169. I thought I did something wrong. I unplugged the power supply, water a little while and plugged it back in, the caps measured as high as 384 fluctuating.

assuming I’m on the right pin, pin 4 of the ic has 0 volts.

I’m not sure I known where the ziner diode is you want me to test

[dholley]

Waited a little while, not water a little while

[R_J]

To get 384 on the main cap means the pfc circuit is turning on, for this to happen the pfc ic U601 must be getting vcc voltage.
Pin 4 of U101 is the feedback pin, it has a zener diode, zd103 (near U101) from pin4 to ground, pin4 also connects to the output of PC101 optocoupler. Check the voltage on JW25 or JW29 (jumper wire near optocouplers)
Have you tried the power supply back in the tv? it may be that the 5 volt line does need a bit of a load to stabilize, or not

[dholley]

Thank you RJ, I appreciate your help. I will work on these items tomorrow. Have a great day!

[R_J]

The out of range readings can be caused by your meter, The pfc circuit generates high frequency to boost the voltage and some meters see the peak pulses.

[dholley]

1. I put the power supply back in the tv. It will not power on. No led light. No standby voltage.
2. ZD 104 - 0.55 voltages one way and OL the other
3. The 5 voltage voltage has dropped it used to be around 5.25 fluctuating, it is now approximately 2 volts fluctuating
4. I don't know what happened, but the readings for Big Caps (169 volts), VCC (9 to 10 volts fluctuating), Pin 4 (0 volts), JW29 (0 volts) are the same whether or not have jumped standby to 5V.
5. Could the approximately 2 volts that I'm getting at the 5 volt output be a problem?

[R_J]

Pin 4 of the ic produces its own voltage, the optocoupler then controls it, so if zd104 is not shorted, maybe the optocoupler is bad. Or the ic itself is damaged and not allowing the ic to operate at full, it is stuck in pulse mode,
Likely without a load the 5v standby eventually charged to 5 volts, once it was loaded down it is only a couple volts, I suspect it will again climb to 5 volts.
The large caps will be at 165vdc without the pfc boosting it to 385vdc. Like I said before, the pfc ic gets its vcc from the standby vcc, if the standby vcc is only 9~10 volts, the pfc would never operate, but the power supply also needs the power supply to be turned on before the pfc works.
Try forcing the power supply on without the main board and see if voltages come up again.
It may be that the ic is bad, and trying to eliminate everything else is hard.

[dholley]

the readings are with the power supply disconnected from the TV. The voltages are the same with and without jumping the standby pin to the 5v with a 1 k resistor.
Do you recommend replacing the IC and all three optocouplers?

I'm attaching pictures of the IC and Optocuplers, note CC013 EL817 is one of the original optocouplers, the two BC125 EL817 were taken from another board. I don't know if the originals were bad, It was just an experiment to see if it would help.

If replacing, do you have recommendation for the replacement parts,

[R_J]

You can try replacing PC101 with one of the originals to see if the voltage on pin 4 of U101 comes up. If pin 4 drops below 350mV the ic enters burst-mode which means it only supplies a few burst of pulses to the transformer. This will result in a low voltage at the secondary (5V)
If pin 4 is not directly shorted to ground bay any external component it must be that the internal components are faulty.

[dholley]

thank you. I will replace PC101 with one of the originals and update with the results.

[dholley]

I installed the original optocoupler and the voltages are the same , 167 at the caps, 9 to 10 at Vcc, 0 at pin 4, 2 volts at the 5 volt output