Author Topic: 2N3904s that are CBE!  (Read 1001 times)

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Offline bjrolfe

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2N3904s that are CBE!
« on: December 21, 2018, 03:49:37 pm »
So, it seems I have a baggie of 2N3904s that are CBE (should be EBC). I used one in an Arduino setup to interface with my alarm system and couldn't figure out why the data line was being partially pulled down to ground (when it shouldn't).  Spun it 180° and started working. Dropped in a 2N4400 and was working correctly (EBC).

Attached some breadboard pics.
Notes: 12V power supply, 1KΩ resistor.

Has anyone else seen this madness?

I've now labelled that baggie as "CBE!!!"

Edit:
Added a pic with the multimeter to show where the extra wires are going to.
« Last Edit: December 21, 2018, 03:53:20 pm by bjrolfe »
 

Online wraper

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Re: 2N3904s that are CBE!
« Reply #1 on: December 21, 2018, 04:07:50 pm »
Where did you get them from?
 

Offline bjrolfe

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Re: 2N3904s that are CBE!
« Reply #2 on: December 21, 2018, 04:19:20 pm »
I bought them from a local electronics store more than 10 years ago.
 

Online RoGeorge

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Re: 2N3904s that are CBE!
« Reply #3 on: December 21, 2018, 04:20:38 pm »
Why is the base of the transistor floating (not connected in any circuit) on the breadboard?

If the red/black wires near the transistor are coming from Arduino (GND and Data line), then your LED is powered by the Arduino data line, and not by the transistor.
« Last Edit: December 21, 2018, 04:33:34 pm by RoGeorge »
 

Offline bjrolfe

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Re: 2N3904s that are CBE!
« Reply #4 on: December 21, 2018, 04:32:45 pm »
Base is not connected to show that it's conducting without any current through the base. The other wires are just off to my multimeter to check the voltage drop over the transistor (see 4th pic).

It's conducting because it's over the ~6V EB breakdown voltage.
 

Offline T3sl4co1l

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Re: 2N3904s that are CBE!
« Reply #5 on: December 21, 2018, 06:02:41 pm »
There's P2N2222A which is a PN2222A (note: not 2N2222(A), that's TO-18!) with reverse pinout.  I wonder if it was a relabel of that, or a "P2N3904" as the case may be?

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Offline bjrolfe

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Re: 2N3904s that are CBE!
« Reply #6 on: December 21, 2018, 07:09:26 pm »
Yes, the labeling does look pretty crappy so might be a relabel of a different part.
 

Online RoGeorge

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Re: 2N3904s that are CBE!
« Reply #7 on: December 21, 2018, 08:04:22 pm »
That's weird, those transistors are very common and cheap, so I see no reason why one would take the effort to re-marking (counterfeiting) them, unless someone was trying to literally sell garbage (parts that fail all tests end up in the dumpster bin of the factory.  Depending on the wealth of the dumpster diver, some might try to sell out-of-spec parts.

Maybe it's a mistake in the datasheet  :)
(well, once I found a transistor pinout mistake in a datasheet, but that was in a local paper-printed catalog, way before the PDF datasheet era)

My best guess is that you bought some other parts that were labeled by mistake as 2N3904 by the factory, so that particular batch was discarded, and the dumpster-diver somehow managed to sell them as 2N3904, even if they are something else.
« Last Edit: December 21, 2018, 08:07:17 pm by RoGeorge »
 


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