P6201 probe Q100 FET replacement

Nenad Filipovic
 

Dear Group,

I got a dead P6201 off eBay, and everything points to a defective input FET
(probe serial B065531). So I obtained a handful of MMBF4416 (code
151-5025-00 in the service manual, factory default for later serial
numbers). Tek also released a product modification document under
050-1413-01 code:

http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Tek/050-1413-01.pdf
same document:
http://hakanh.com/dl/docs/kitinstructions/050-1413-01.pdf

outlining this replacement. The problem I have now is that drain and source
of the 151-5025-00 FET in the above document are reversed compared to
MMBF4416. None of the datasheets for MMBF4416 say it's symmetrical, and I
somehow doubt an RF JFET would be without optimizations on the drain side.
This comment however states it is symmetrical:

https://groups.io/g/TekScopes/message/131217

but I see no facts this claim is based on. Does anyone have direct
experience with this particular replacement and D-S polarity? Disassembling
the probe head is a pain, I'd like to get this right on the first go.

Best Regards,
Nenad

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