Diode test,N channel mosfet replacement

[supersabre]

My LCD inverter keeps shutting down after being switch on for 2-3 second.

I swap everything(screen, button, video board, power supply) with a good monitor, and it is still the same

There are 2 mosfets that drives the 2 transformers.
The voltage on the mosfet's drain is normal (Compare with the good one)for 1 second and then it jumps to 17V. then backlight is off

I check the mosfet which is a AOD 444, N channel, 60V,12A.

https://cdn.badcaps-static.com/pdfs/...0b37976c7a.pdf

I use the diode checking on the multimeter to test whether there are anything funny with the mosfet and compare the readings with the good one.

Everything is noraml except when i use the diode check for drain and source.

The mosfet on the good board will have 500ohm, and the mosfet on the bad board will have 540.

I reverse the black and red probe for checking the drain and source on mosfet. The mosfet on both board are infinte.

Question: Does 40 ohm difference in diode test indicate the mosfet is bad?

I find a similar mosfet



,but the mosfet power dissipation is 48w, the bad one (AOD 444) is 20w according to datasheet



Question2: What're the important parameters when substituting mosfet in inverter? Is bigger mosfet power dissipation good or bad for the inverter?

[hardwareguy]

Re: Diode test,N channel mosfet replacement

Bigger power dissipation ability is nice, the more the merrier!

The biggest parameters are voltage, current and gain. Of course, whether it's a P channel or N channel is also critical as is the package type.

[hardwareguy]

Re: Diode test,N channel mosfet replacement

The voltage and current rating MUST be equal or greater than the old one and gain should be similar.