geforce mx4000 128mb strange fets
i have that video card but before trying it on my motherboard i have checked its two mosfets and the ohmeter reads a short between drain and source on both of them.Both mosfets look good.When testing drain to gate it reads open circuit the same goes for gate to source open circuit ( infinite resistance) but the short appears when reading drain to source.Any ideas?
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Re: geforce mx4000 128mb strange fets
Those mosfets are probably connected in parallel with each other. If so, they'll both show the same readings in circuit.
How short is it? If it's on the order of 10's of ohms then that's not unusual in-circuit and it might be fine. But if it's < 1 ohm then something must be shorted. I might try it on a board/PSU I didn't care much about just to be sure before I start working on it. A good quality PSU should shut off if it detects an overload, but it's still not really good for it.
I'd check with a multimeter to find which capacitors are in parallel with those mosfets, and remove them. Then see if the mosfets still show a short. If so, then lift the mosfets' legs off the board and figure out which one is bad. One of them will probably still test good but it might have been partially damaged, so if you want the ideal repair it's probably best to replace both of them.
I've had a few shorted mosfets and not yet seen one that didn't look good, so I wouldn't judge them by appearance.
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