Vizio E550i-b2e no standby voltage

[Mbd3]

Hi All, I have a vizio e550i-b2e that has no standby voltage. I am hoping some one can help. I am getting 10-14volts bouncing at pin 5 of ic901 (Vcc). According to the data sheet for that ic I need atleast 16v for it to turn on. I did a thermal scan and the only thing that glowed was d901.

[dskall]

Re: Vizio E550i-b2e no standby voltage

You need to check all diodes, caps, resistors, mosfets around IC901for shorts and opens.

[Mbd3]

Re: Vizio E550i-b2e no standby voltage

I have. Everything checked as it should. I was wondering if maybe that d901 is stealing current from ic901? Maybe the diode is a little leaky? Sorry I am a complete newbie.

Thanks

[dskall]

Re: Vizio E550i-b2e no standby voltage

Can you post datasheet?

[R_J]

Re: Vizio E550i-b2e no standby voltage

Replace C907 and C904B, Do you have any voltage at D950B cathode?

[Mbd3]

Re: Vizio E550i-b2e no standby voltage

I did replace the capacitors and I am trying to find the d950.

[nomoresonys]

Re: Vizio E550i-b2e no standby voltage

D950b is right by connector cn101, looks like they did not use D950a.

[dskall]

Re: Vizio E550i-b2e no standby voltage

No short between pin 1 and 7/8 of IC?

[Mbd3]

Re: Vizio E550i-b2e no standby voltage

Ok thank you. I have 0volts on D950B.

[Mbd3]

Re: Vizio E550i-b2e no standby voltage

No everything looks good. From my understanding the ic takes current for the drain pins 7 and 8 and applies it to start the pwm then charges the cap for vcc. Then the aux winding is suppose to take over. However like I said the Vcc doesn't go over 14.5v and it needs 16 to turn on.

[R_J]

Re: Vizio E550i-b2e no standby voltage

The vcc voltage you are seeing on pin5 is likely from the internal startup cell, Check the source resistors, R907a,b if they are ok, I suspect the ic itself could be bad, if it was trying to start you should see a volt or two on D950b as that is the output of the standby voltage, just be sure there is no short on the standby output killing the voltage

[Mbd3]

Re: Vizio E550i-b2e no standby voltage

I have put 3 ics in so far same results. I had the 5v stand by and then gone and can't get back.

[Mbd3]

Re: Vizio E550i-b2e no standby voltage

You can see everything looks normal except for D901

[Mbd3]

Re: Vizio E550i-b2e no standby voltage

I know I can buy a new board, but now this is a pride factor I will not let a board beat me lol

[dskall]

Re: Vizio E550i-b2e no standby voltage

So did you have shorted pins on the ic's you replaced?

[Mbd3]

Re: Vizio E550i-b2e no standby voltage

No everything checked good.

[R_J]

Re: Vizio E550i-b2e no standby voltage

I have put 3 ics in so far same results. I had the 5v stand by and then gone and can't get back.

What other parts have you replaced and did not mention? What did you do that caused the 5v standby to die? did you short something?

Check that you don't have an open transformer winding between pins 1&4 and also the output pins 5&7

[Mbd3]

Re: Vizio E550i-b2e no standby voltage

I replaced all together IC901, C907, C904B, C903, C901, Q800, andR804A

[R_J]

Re: Vizio E550i-b2e no standby voltage

What was wrong with Q800 & R804A? they are for the pfc circuit not the standby circuit. however if Q800 was shorted it may have damaged ic801 and ic801's vcc voltage is supplied by the standby circuit D902 via the transistor connected to J14
Also if ic901's internal mosfet shorted, it may have damaged the source resistors or shorted zd909, zd909 would need to be removed to check it because it is across the low value source resistors R907.

[nomoresonys]

Re: Vizio E550i-b2e no standby voltage

maybe look all the solder joints over closely, might be just the picture but the joints on BD1 and D120 look a little suspect.