"Mark Zacharias" wrote in message
...

Just the other day had two relay drive transistors in a Marantz 2270 with
an
hFe of 2. Don't know for sure how or why they failed, but I did notice
black
tarnish on the leads. Perhaps migrated into the semi material?

Black tarnish on the leads... Good catch, that's probably one more of those
things to watch for (like yellow glue turning conductive and similar
horrors).

Yesterday I've had a set of 5 identical transistors, previously unused but
of
unknown age (sitting in a drawer from before my time) all fail with CB break
down around 10V (supposed to be around 50V) when I put them into a prototype
and powered the thing up. The transistors (a drawer full of them) have no
traces of being used previously (solder remains after being desoldered, bent
leads, or anything else), they look totally unsuspicious, except from a dark
tarnish on the leads. Yet they don't work. Leaky like hell, even with the
base resistively pulled down to the emitter, and up from ca. 10V they just
go
ohmic (no avalance or such thing, more like extreme leakage). The device's
whole function went haywire and took me some hours to figure out why.

So beware of transistors in TO-92 (or otherwise) with black tarnished leads.

Regards
Dimitrij