I've found FETs that were etched with the part number but were in fact BJTs.

I ordered a bag of 2N7000 MOSFETs from AliExpress and there were a few, but most tested as 2N2222 BJT transistors.

 

Pardon me if I interrupt, but were they 2N2222's or 2N2222A's?

 

Based on what @sarahMCML said, I put several TO-92 cased regulators in the Old Tester and the atlas DCA. In the Old the 78L05 tests as "part unknown or damaged" and shows a diode symbol. The DCA tester recognizes it as a regulator and gives its tested specs. The TL431A in the Old tests as 2 Diodes between the 3 pins and gives their Vf values. The DCA tests it as a "NPN digital BJT" and gives it an hFE of 4390! It also gave it a pin out of BCE, hmmm. The Old tests the LM317L as "part unknown or damaged" and shows a diode symbol. The DCA shows it as a voltage regulator and gives its tested specs. So, the TL431 also fooled the DCA due to its complex structure.

 

Pardon me if I interrupt, but were they 2N2222's or 2N2222A's?

Not sure. They were unmarked except for a couple.

 

@djsfantasi Just did a grab sample of the 100 lot of 2N7000s that came in with the bad FETs. Checked 15 randomly and they all test as N-E-FET on the old tester. The one thing I do wish that the DCA had is a ZIF block instead of its 3 minigrabbers. Too slow and awkward to put DUTs into the DCA's minigrabbers even if it does give far more test data on transistors. Hard to beat the chinesium tester for a quick grab test.

 

The one thing I do wish that the DCA had is a ZIF block instead of its 3 minigrabbers. Too slow and awkward to put DUTs into the DCA's minigrabbers even if it does give far more test data on transistors.

Could the mini grabbers be the problem? If the mini grabber isn't making contact on the emitter, the collecter and base make a diode, don't they? https://en.wikipedia.org/wiki/Diode-connected_transistor

 

Nope, both minigrabbers and ZIF sockets make very good contact. Sometimes on old and oxidized resistors I will "twist" the minigrabbers to cut through the oxidation to make good contact. That was not the condition of these "transistors" or whatever they are. I often see references to transistors being used as diodes and even as zeners but never used one as that myself. I plan to do some experimenting with and have an archived article about it to reference.

 

Too slow and awkward to put DUTs into the DCA's minigrabbers even if it does give far more test data on transistors.

You could attach the minigrabbers to a ZIF socket.

 

The TC1 Tester actually comes with a set of short cabled minigrabbers to insert the other end into the ZIF socket to use on in-circuit devices. It's the minigrabbers that are awkward and time consuming to connect. Much easier, for me at least, to use a ZIF socket. That said, I use minigrabbers on my DMMs most of the time instead of the Prong Probes. I can handle a pair of chopsticks well enough but never really liked using the Prong Probes.

 

Hello, do your minigrabbers tip protruded out a little so that they can be used as probes?

 

Nope, they fully retract unless grabbing the leg of a component. Sometimes I'll clip them on one end of a 12cm Dupont male to male jumper to either use as a LO voltage probe or stick into a breadboard