How I found a bad FET:
http://www.repairfaq.org/sam/semitest.htm#stmos
"(From: Bruce (reglarnavy@aol.com).)
You can get a pretty good idea about the condition of a MOSFET with some quick & simple bench tests. The first thing you can do with a meter is measure the parasitic substrate diode that connects the drain to the source. In an NMOS part, this diode's cathode will be at the drain, and the anode at the source. It will meter out similar to any conventional diode in both fwd / reverse directions. You can see this diode in the schematic representation of the FET in some databooks and a few schematics. The FET should show infinite resistance, gate - source and gate - drain. If it does not, then the gate oxide may be blown."
There's a lot more you can do then that, but it's all I had to do to find it.
I had found out what pins did what by searching mouser for the part #, then opening up a datasheet from one of the compatible matches.
http://www.fairchildsemi.com/ds/HU%2FHUF75545P3.pdf
They were still on the board connected to other stuff when I first tested them, so they didn't react as in the above description. However I was still able to find one that was way off the mark. After removing it from the board, I tested it again and confirmed that it's bad.
I did find a warning regard dead FETs and controllers:
http://www.uoguelph.ca/~antoon/gadgets/mostest.htm
"When MOSFETS fail they often go short-circuit drain-to-gate. This can put the drain voltage back onto the gate where ofcourse it feeds (via the gate resistors) into the drive circuitry, prossibly blowing that section. It will also get to any other paralleled MosFet gates, blowing them also.
So, if the MosFets are deceased, check the drivers as well! This fact is probably the best reason for adding a source-gate zener diode; zeners fail short circuit and a properly connected zener can limit the damage in a failure! You can also add subminiature gate resistors -- which tend to fail open-circuit (like a fuse) under this overload, disconnecting the dud MosFet's gate."
In other words, the driver on my controller is probably blown...
Still I read this:
http://www.uoguelph.ca/~antoon/gadgets/mostest.htm
"Dying MOSFETS often emit flames or blow-out, even more so in hobby built electronics projects. What that means is that a defective unit can usually be spotted visually. They show a burned hole or 'something black' somewhere. I have seen them alot especially in ups's which can have as many as 8 or more mosfets in parallel. I always replace all of them if a couple are defective plus the drivers."
Mine looks no different then the others...
http://www.repairfaq.org/sam/semitest.htm#stmos
"(From: Bruce (reglarnavy@aol.com).)
You can get a pretty good idea about the condition of a MOSFET with some quick & simple bench tests. The first thing you can do with a meter is measure the parasitic substrate diode that connects the drain to the source. In an NMOS part, this diode's cathode will be at the drain, and the anode at the source. It will meter out similar to any conventional diode in both fwd / reverse directions. You can see this diode in the schematic representation of the FET in some databooks and a few schematics. The FET should show infinite resistance, gate - source and gate - drain. If it does not, then the gate oxide may be blown."
There's a lot more you can do then that, but it's all I had to do to find it.
I had found out what pins did what by searching mouser for the part #, then opening up a datasheet from one of the compatible matches.
http://www.fairchildsemi.com/ds/HU%2FHUF75545P3.pdf
They were still on the board connected to other stuff when I first tested them, so they didn't react as in the above description. However I was still able to find one that was way off the mark. After removing it from the board, I tested it again and confirmed that it's bad.
I did find a warning regard dead FETs and controllers:
http://www.uoguelph.ca/~antoon/gadgets/mostest.htm
"When MOSFETS fail they often go short-circuit drain-to-gate. This can put the drain voltage back onto the gate where ofcourse it feeds (via the gate resistors) into the drive circuitry, prossibly blowing that section. It will also get to any other paralleled MosFet gates, blowing them also.
So, if the MosFets are deceased, check the drivers as well! This fact is probably the best reason for adding a source-gate zener diode; zeners fail short circuit and a properly connected zener can limit the damage in a failure! You can also add subminiature gate resistors -- which tend to fail open-circuit (like a fuse) under this overload, disconnecting the dud MosFet's gate."
In other words, the driver on my controller is probably blown...
Still I read this:
http://www.uoguelph.ca/~antoon/gadgets/mostest.htm
"Dying MOSFETS often emit flames or blow-out, even more so in hobby built electronics projects. What that means is that a defective unit can usually be spotted visually. They show a burned hole or 'something black' somewhere. I have seen them alot especially in ups's which can have as many as 8 or more mosfets in parallel. I always replace all of them if a couple are defective plus the drivers."
Mine looks no different then the others...
