[sdiy] odd behavior of transistors

[jhaible]

> In my current project I have used a 2N3904 at the trigger input. I
> noticed today that this transistor was responding backwards to the
> triggers! That is it was opening with a ground and closing with a gate.
>
> I pulled the part out and put another in. Problem solved. Does this
happen?

If the transistor was used as a logic inverter, and was damged such that
BE is open, but BC is shorted, something like you described seems
possible.


> Has anyone in Germany noticed a high margin of bad parts in orders form
> Reichelt? I have found at least one bad chip on each channel of my new
> sequencer. That's 5 chips that didn't work from the onset. When they
> were replaced by chips from another source, everything was fine. They
> have been 4067, 4514 so far, plus the 2N3904. Am I the one who's crazy?
> I guess that's why they're cheap.

I have never received _bad_ parts from Reichelt, but a lot of _wrong_ parts.

The LP324 instead of LM324 was the most recent example. (I guess the read
"improoved" in the data sheet and think they can just "upgrade" you without
asking.)

Same for NE5517 instead of LM13600. Just not the same thing.

The *worst* thing are HCMOS chips instead of 4000 series CMOS.
I almost *bet* that your "4514" is actually a ST "HC4514", which is
in fact ST's version of the 74HC4514 (4000 series functionality
adapted to 74HC family technology) and *not* a version of the
CD4514, MC14514 or HEF4514. So you have a 5V chip with 6V
maximum rating, not a 15V chip with 18V rating.
At least this is what happend to me.

Recently I got "V4007" when I ordered Reichelt's "MOS4007".
I think these are surplus DDR (GDR) clones of the 4000 series,
but I may be wrong and it's something else. At least these *work*
on 15V. (;->)

I had a lot of discussions with Reichelt about similar incidents.
There is no hope - they say we are unexpensive, what dou you
expect. (I'm paraphrasing.) And in a way they are right - they
are cheap. And they always offered to take the wrong parts
back. And they are the best (only?) source of Japanese semiconductors
in Germany, so I'll still buy from them, despite some irritation.

JH.