phillips lcd keeps blowing fuse

[TimT]

phillips 40pfl3505d/f7 lcd keeps blowing fuse on power board right by ac input. any idea why?

[Mr Bill]

Re: phillips lcd keeps blowing fuse

Have you checked any/all of the diodes on your power supply? Mosfets too.

[Dgtech]

Re: phillips lcd keeps blowing fuse

I agree. There are usually just about four components that will cause this and one is a very common failure - the bridge rectifier. As Mr. Bill says too, the mosfets are another cause of this problem as well.

With the power disconnected, measure resistance from both fuse tabs to chassis ground.

[TimT]

Re: phillips lcd keeps blowing fuse

is that something that can be done with a multimeter and no power to the board?

[gilly1984]

Re: phillips lcd keeps blowing fuse

Yes.

[senndogg]

Re: phillips lcd keeps blowing fuse

put the multimeter in the "Ohm" section and measure the 4 diodes one by one, or if your psu has a big bridge rectifier measure the 4 pins, alternating the probes. if you get 0 Ohms that means a diode (or more) is shorted.

[TimT]

Re: phillips lcd keeps blowing fuse

about the only way i can get a reading is to set meter to 20m or 20k is that correct?.. here are some pictures of the power board im not 100% . sure what a bridge rectifier is but i think i have it circled alone with a diode and something else im not sure what its called . ..sorry im still learning

[tom66]

Re: phillips lcd keeps blowing fuse

Set the meter to the range which looks a bit like this ->|-

If that highlighted diode reads zero in both directions it could be the fault. On these power supplies (resonant self-oscillating, no intelligent control) a shorted output will blow the fuse.

This is a bridge rectifier, typical appearance on a power supply:
http://media2.rsdelivers.catalogueso...7005465-10.jpg

[TimT]

Re: phillips lcd keeps blowing fuse

I noticed that >| thought i had it set wrong.. theres alot of diodes to test..wil do that after dinnner! when you say " reads zero in both directions " are you talking about taking a reading then switching probe ends around ie.+ - then -+...thanks

[tom66]

Re: phillips lcd keeps blowing fuse

Yes... and by zero, I should say, anything less than about 100 is most likely shorted, but almost every diode I have had fail does so at dead zero (or a few millivolts) in both directions.

[TimT]

Re: phillips lcd keeps blowing fuse

well if I was testing correctly there's about 60 bad diodes! some were good but 95 percent were bad
I had the multimeter set on 200... best just to buy a new board?

[Mr Bill]

Re: phillips lcd keeps blowing fuse

What brand is your multimeter, or post a picture of it. I'm thinking your doing something wrong. The meter needs to be set to diode mode. You should get a reading and when you reverse the probes you should get OL.

[TimT]

Re: phillips lcd keeps blowing fuse

the meter is a Etek. the pictures show the settings and how i test.

[Mark369]

Re: phillips lcd keeps blowing fuse

what your testing in pic no 2 is a resistor not diode. turn your metre one more clockwise.
that is the diode mode.

[TimT]

Re: phillips lcd keeps blowing fuse

I know thats was not a diode..i was just trying to show the way i test. i was hoping i had done something wrong! lol ok i will retest again with the right setting. thanks

[TimT]

Re: phillips lcd keeps blowing fuse

ok just noticed im getting a beeb from the meter when testing some diodes???

[Mr Bill]

Re: phillips lcd keeps blowing fuse

what is the meter displaying when it beeps?

[Mark369]

Re: phillips lcd keeps blowing fuse

its good if you get beep only one way.

[TimT]

Re: phillips lcd keeps blowing fuse

got a beep both ways on one diode. it displays 0.24 on meter when it beeps. seems to be about 4 bad diodes.. read about 5 to 6 then when i change ends with the probe I get 1... i think thats 0 How do i identify the diodes so i can buy the correct ones?

[budm]

Re: phillips lcd keeps blowing fuse

Are you testing them still on the board or lift one leg off the board? To be accurate, you should at least lift one leg off the board and measure them again.