50PK750 keeps blowing resistor!! HELP

[football0062]

Have a LG model 50PK750. has the EAY60968801 power supply with the 2 resistors in the top right.

The problem is it keeps blowing either of the power resistors(22Ohm 5W) after shutting it down and turning back on.

Ive replaced it with a used power supply which did the same thing
Ive rebuilt the power supply and replaced the current control IC and Diode
Ive replaced the Y sustain board and upper and lower buffer boards.

attached pictures of the power supply. in red is the power resistors that keep blowing. in blue is the current control IC and diode i replaced.

once it blows the resistor it turns on for a quick second and clicks back off.

[tom66]

Re: 50PK750 keeps blowing resistor!! HELP

Are you using "pulse rated" resistors? They are used to discharge Vs/Va on power off so have to withstand a large current pulse.

[football0062]

Re: 50PK750 keeps blowing resistor!! HELP

i wish i had the datasheet for it but im using these 5WJ22.

[tom66]

Re: 50PK750 keeps blowing resistor!! HELP

You might have to source some alternatives. They are probably generic 22 ohm resistors. Peak power dissipation will be 1,910W (205V Vsus assumed), so general purpose ones will just fuse open.

[football0062]

Re: 50PK750 keeps blowing resistor!! HELP

what would you recommend?

[football0062]

Re: 50PK750 keeps blowing resistor!! HELP

and yes vs is right at 205V so ur correct on the power dissipation

[football0062]

Re: 50PK750 keeps blowing resistor!! HELP

what do you think about this one?

[tom66]

Re: 50PK750 keeps blowing resistor!! HELP

Can you get the AC03,AC04,AC05,AC07 or AC10 series? (Other ones will be no good.) Charts on page 5 show max peak power is too low for AC01. Try and get as high as possible (AC10 is highest)

[football0062]

Re: 50PK750 keeps blowing resistor!! HELP

i ordered the AC10 its a 7W 22ohm from digikey. i fly out to see family for a week tomorrow so part should be here when i return and i will post my findings. thank you

[football0062]

Re: 50PK750 keeps blowing resistor!! HELP

so far so good, keeping fingers crossed

[budm]

Re: 50PK750 keeps blowing resistor!! HELP

Do you have the diagram of the board, the resistors look to be connected in series (one for discharging through the MOSFET, and one of for supplying the VS) at the junction is connected to the Cathode of a diode, and the other end is connected to the Drain pin for discharging?

[tom66]

Re: 50PK750 keeps blowing resistor!! HELP

I don't have a diagram myself but the way it usually works is Vs connects to FET drain through 22 ohm resistor, and Va connects to same FET through another resistor. The transistor is turned on by the control IC on power fail to discharge Vs/Va.