Vizio m65-c1 Power supply board

[electronicartist]

Having a problem finding the problem on the power supply board. The board turns on and off in a 2 hz pattern. Checked the input capacitors and they are all good and never drain even after remove the input supply. Tested all the mosfets and they check out good. Checked the opto isolators and they are good. Checked the diodes and they check out good. Checked for open resistors and they good. The power supply has 12 and 24 volt output the 12 volt is the one pulsing and there is no 24 volt output it has a ps_on and i tried to ground it to see if the 24 volt would do something but it does not turn on.
Board PN is ADTVE1835ACB
tv is maybe a year old. seems as though what happened was maybe a spike in the line damaged something.

 

[ronsimpson]

I really don't know this power supply. It seems to me that the 12 and 24 should come up together. I would check the 24V diodes again.

2 hz pattern

That is typical of a power supply that is in trouble.

 

[electronicartist]

Okay I have gandered at the board and probed with the o silly scope and found a diode that has .4 volt bias and 1.5 reverse, that cant be good. also have a resistor that supply's this that seems to be also wrong. the smd resistor reads 1R80 what looks to be anyway and ohm's out to be 152k ohms. I think the resistor should be 1.8 ohms but i dont know how many watts its extremely small, i'm think 1/10th not sure here. the diode probally should be fast acting.

 

[electronicartist]

Here are some pictures

 

[electronicartist]

Replaced the diode and the smd resistor and so far so good.

 

[CompEngineer]

electronicartist - Thank you for posting what you found. I have the same board and looks like the same issue. There is a burn hole in my resistor and the same diode is bad. Could you say what specs you used to replace those two parts? Was the resistor a 1.8ohm, 1/2watt, 1%? Any help in getting a correct diode? I stole a diode from a dead power supply board that is .5v biased so I'm assuming that will work.

 

[electronicartist]

electronicartist - Thank you for posting what you found. I have the same board and looks like the same issue. There is a burn hole in my resistor and the same diode is bad. Could you say what specs you used to replace those two parts? Was the resistor a 1.8ohm, 1/2watt, 1%? Any help in getting a correct diode? I stole a diode from a dead power supply board that is .5v biased so I'm assuming that will work.

Resistor is 1.8 ohm 1/4 watt 1% Diode is 1amp 1000v fast acting 1.3v forward

 

[CompEngineer]

Thank you!