A Hive-Mind Quandary on J201 JFETs

[Cybercow]

Here's one for the hive-mind . . . . .
Out of a batch of 100 genuine NOS Fairchild TO-92 J201 JFETs, I found three that test as dual-diodes on my Peak Atlas DCA-75. But when I try them in a circuit, they perform just the others that test as actual JFETs.
The DCA-75 was fully charged, so PS is not an issue.
I can't help but think that maybe those three J201s are just so perfectly balanced, they're confusing the Peak Atlas.
Thoughts? Ideas?

 

[Robert]

My DCA75 (and ZEN50, and TC1) incorrectly identifies 1.8V zener diodes as 3.3V zener diodes.

 

[KreoPensas]

Huh.

A lot of SMD j201's I recently soldered for a Deofol tested as dual diodes. I set them all aside as mysteries. This has happened with a number of 2SK209's as well.

I suspected error on the part of the chinesium LCR tester. Now I really wonder. Test circuit time I reckon. But wtf am I checking for other than operation?

 

[JTEX]

If they work as expected in-circuit, I'd say that's the gold standard. Who is DCA75 to say otherwise? I tested and sorted all my MMBF201's in-circuit.

 

[owlexifry]

Thoughts? Ideas?

what if you tried a different test method...

multimeter and rg keen method works for me every time.

 

[Matopotato]

I got a batch of 5 J201s. Only one showed values with DCA75, the others were either "not connected" or "2 diodes" depending on the pins to DCA-connector combinations.
So I breadboarded the Greatly improved JFET matcher II as linked above.
I tested the working one and a 2N5457 in both and got varying results.
The working J201 came out Idss=0,35mA and Vg(off)=-0,58V in the DCA75, and the breadboarded setup gave me 0,40mA and -0,66V respectively.
Oughtn't they come up the same or quite a bit more close?
Can I use a factor of 0,35/0,40 to adjust the DCA-failing ones to DCA-comparable values? Or is it not that linear between the two methods?

 

[Cybercow]

I got a batch of 5 J201s. Only one showed values with DCA75, the others were either "not connected" or "2 diodes" depending on the pins to DCA-connector combinations.
So I breadboarded the Greatly improved JFET matcher II as linked above.
I tested the working one and a 2N5457 in both and got varying results.
The working J201 came out Idss=0,35mA and Vg(off)=-0,58V in the DCA75, and the breadboarded setup gave me 0,40mA and -0,66V respectively.
Oughtn't they come up the same or quite a bit more close?
Can I use a factor of 0,35/0,40 to adjust the DCA-failing ones to DCA-comparable values? Or is it not that linear between the two methods?

Check the Peak Electronics site for the latest firmware update on the DCA75 Pro.

 

[Matopotato]

Check the Peak Electronics site for the latest firmware update on the DCA75 Pro.

Did it change quite recently?
Got the unit a few weeks ago and it says 0029. Is there an even newer that "fixes" this?

 

[darwin999]

I tested the working one and a 2N5457 in both and got varying results.
The working J201 came out Idss=0,35mA and Vg(off)=-0,58V in the DCA75, and the breadboarded setup gave me 0,40mA and -0,66V respectively.
Oughtn't they come up the same or quite a bit more close?

They are only going to be close if they're measured under close to the same conditions - e.g., same bias current or voltage, etc.

 

[Cybercow]

Did it change quite recently?
Got the unit a few weeks ago and it says 0029. Is there an even newer that "fixes" this?

The DCA75 Software/Firmware Changelog says that 0029 is the latest. Unfortunately, the Changelog doesn't state the release dates. But the Changelog itself was last updated in July, 2026. (Indicated by examining the Changelog PDF document information.)