I am testing an NPD603AL (N-Channel Logic Level Enhancement Mode Field Effect Transformer) from an old Comapq Proliant 1500 CPU daughterboard. Symptoms are no post / no video, with only the psu / blackplane / cpu daughterboard and CPU in place.
First question: This is not explicitly listed in the datasheet title as a MOSFET, however in the description it states it uses D-MOS technology. I assume this means it's just a MOSFET, and the "logic level" means it only needs 5v gate-source charge instead of 10v. Is that correct?
I am testing this because when the CPU is in the socket there is no POST but this FET get VERY hot. Within a minute the heatsink will burn your finger. With the CPU removed the FET does not get hot at all.
When I tested the FET on the board I found drain-source was shorted with the power off. I removed it from the board to isolate. Motherboard showed no short between the empty source and drain pads after the FET was removed.
Measuring the FET with multimeter in diode mode:
Follow-up resistance testing showed OL in both directions. So I'm a little confused. I would expect the drain-source to be fully shorted and read close to zero ohms.
Second question: Could this be a partial failure? (Not fully shorted) or is this FET allowed to read 1.7v in this direction?
Maybe it was initially reading a short on the board because the FET got so hot it shorted, and after it cooled down it is not a complete short? Or maybe there was some residual voltage at the gate? (board was out and on my desk though)
First question: This is not explicitly listed in the datasheet title as a MOSFET, however in the description it states it uses D-MOS technology. I assume this means it's just a MOSFET, and the "logic level" means it only needs 5v gate-source charge instead of 10v. Is that correct?
I am testing this because when the CPU is in the socket there is no POST but this FET get VERY hot. Within a minute the heatsink will burn your finger. With the CPU removed the FET does not get hot at all.
When I tested the FET on the board I found drain-source was shorted with the power off. I removed it from the board to isolate. Motherboard showed no short between the empty source and drain pads after the FET was removed.
Measuring the FET with multimeter in diode mode:
- Source(+) and drain(-) the source I get the 0.5v diode reading as expected.
- Source(-) and drain(+) I expect to see OL but got 1.7v.
Follow-up resistance testing showed OL in both directions. So I'm a little confused. I would expect the drain-source to be fully shorted and read close to zero ohms.
Second question: Could this be a partial failure? (Not fully shorted) or is this FET allowed to read 1.7v in this direction?
Maybe it was initially reading a short on the board because the FET got so hot it shorted, and after it cooled down it is not a complete short? Or maybe there was some residual voltage at the gate? (board was out and on my desk though)
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