Sub for MFE-3002, MFE3002

[cncjerry]

Last week when I picked up the Fluke 332D I also brought home a Dial A Source 46A.  This is another voltage standard having a pretty decent KV divider and two ranges, +/-10 and +/-1.

The unit was working well, seemed stable after being left on as recommended, until I noticed the output was sitting at -14 instead of +10.  In tracing through the schematic, I isolated the problem to the output/sense amplifier referred to as a CSA.  It is meant to be replaced and no discrete schematic is provided.  I've since sent a note to the parent company as they still sell a follow-on model.

I checked all the diodes, caps and transistors.   The +15 was low and I didn't realize until later that there was a bad cap in the power supply.  I'm starting to think that might have cause the chain of events that took out the CSA board. The board also has two LM308H op amps which I didn't check and two MOSFETs, MFE3002 type.  As near as I can tell they are general purpose low voltage amps/switches.   There is clearly a big difference between the two MOSFETS while doing a simple diode and resistance check and consequently, of course, the most unobtainable part is the one that seems to be failing.

Looking online I found a place in the UK that claims to have them and I sent them a note. 

Optimistically, I am posting here to see if anyone knows anything about them and if so, can recommend a common sub?  They are listed simply as a 20V N-Channel switch.  By the way, they are 4-leggers in a can.

For those that like pictures, here's the DAS-46A, MOSFETS and CSA board.  I'll be cleaning the board when reassembled.  Also, I have the sense and output links open for debugging.

Thanks

[KhronX]

Some quick googling revealed this:
http://www.ersinelektronik.com/class/INNOVAEditor/assets/Datasheets/MFE3002.pdf

Seems like they are indeed some pretty standard-ish low-voltage MOSFETs.

Regarding the TO-72 package, this document has several pinout variants:
https://www.centralsemi.com/PDFs/case/TO-72PD.pdf

Pin 4 always seems to be connected to the case, apparently - that should be easy enough to check, though

[r6502]

Hello cncjerry,

I also own a DAS, but a different model. Mine is the DSA 56a, and has also a CSA build in, that is currently nor working. It could also  be addressed to the MOSFETs but I'm not sure. Dit you get your model back working?

I took a look on your CAS that looks similar to mine, so I think, GR puts the same CSA in different models.

I have also drawn a schematic of the CSA. You can find it here:
https://www.eevblog.com/forum/metrology/general-resistance-das56a/25/

Guido