Vizio TV E470VL SMPS Flucuation Output Voltage

[dholley]

Would someone please help troubleshoot a Vizio 47" TV Switch Mode Power Supply with 5 volt output fluctuating voltage. The voltage fluctuates at 5 the volt output and at the Pulse Switch Modulating IC at VCC. I have the following notes:

1. The 3 main filter caps all have approximately 167 volts steady
2. I have replaced 4 mosfets next to what I think is called the inventor transformer (big black transformer) pictures attached
3. I have replaced Fuse F102 with an equivalent
4. I have check all diodes and caps and they seem to be ok
5. I replaced the 431 chip at U201

Pictures attached for reference

thank you for your help!!

[stj]

opto isolator(s)
feedback sets the output, if the feedback is screwed then the output will be screwed.

[R_J]

Is F102 the main fuse? was it open (blown)?
Have you tried replacing C104 & C105?

[dholley]

F102 is not the main fuse. It was open. It is near one of the big filter capacitors, C809.
My ESR meter shows C104 & C105 to be ok. Should I test with capacitance meter?

[nomoresonys]

Touch up some of those solder joints.

[R_J]

Ok, I see which fuse it is, What voltage do you get on the 12 volt output? It is supplied by the same transformer so maybe it is loaded down and effecting the +5 volts as well.

[dholley]

I don’t think it is on. Can you tell me how to jump the pins to turn it on or is there another place I can measure that will accommodate your request?

[R_J]

It is hard to trace the circuit using pictures, I will guess there is a transistor that switches the +12 volts, likely the to220 next to C201.
It would seem ic101 is shutting down, what is the number on ic101?
The pin to turn on the power supply seems to be STANDBY, but I don't know if it needs to be grounded or taken to +5v with a 1k resistor.
The ON/OFF pin seems to be for the backlight circuit

[dholley]

I just measured, there is NO 5 volt or 12 output. The 5 volt was fluctuating from 3 to 4 volts but is now 0 volts. The big capacitors were at 167 volts they are now at 171 volts. I don’t know what happened.

[dholley]

When say Ic101, do you mean U101? If yes that is the pulse modulating chip. 00465R

[R_J]

Did that fuse you installed go open again? Yes that should have been U101, I think that is FSQ0465R

[dholley]

The fuse is good. I think you are correct Q0465R

[R_J]

If you have 165vdc on u101, pin 1 (drain) I suspect the ic is bad

[dholley]

Using a big cap for negative, red lead of multimeter to pin one of the IC, there is a huge fluctuation anywhere from 34 to 151 volts

[dholley]

I had the multi meter set incorrectly, the voltage is 170.1 volts

[R_J]

Check the u101 vcc voltage, if 0 check that zd104 zener diode is not shorted, Also check that R105 is not open

[dholley]

It is a fuseable resistor at 0.10 ohms. Did You see my previous post 170.1 volts at the drain?

[R_J]

Originally Posted by dholley

It is a fuseable resistor at 0.10 ohms. Did You see my previous post 170.1 volts at the drain?

I edited my post after seeing yours

You can check the voltage one each side of R102 (using hot ground, main cap negative) one side will be 165vdc the other side will be the ic's str voltage that supplies the internal vcc startup cell, this needs to be above +12vdc and usually around 20vdc

[dholley]

VCC Fluctuates between 9 and 11 volts, zd104 is not shorted, r105 is not open testing in circuit

[R_J]

Originally Posted by dholley

VCC Fluctuates between 9 and 11 volts, zd104 is not shorted, r105 is not open testing in circuit

This tells me the ic is supplying the startup vcc but T201 is not supplying the run voltage.
Check the voltage On D102 cathode, that should be around 20v