Re: Are your transistors growing whiskers in their old age?

David Holland
 

I've not seen it in transistors, but I have seen it in a potentiometer
once. (B&W TV contrast control IIRC). High voltage seems to make it more
likely - also IIRC :-)

David

Sent via mobile annoyance thingy, please pardon any typos.

On Mon, Mar 2, 2020, 11:00 PM John Williams <books4you@...> wrote:

I suspect that many of you already know about this problem, but it is new
to me. It relates to a number of 1960s era transistors causing failures in
transistorized radios. The types of transistors described to have this
behaviour are also used in early Tektronix equipment including the 321 and
321A oscilloscopes. According to the UK radio restorers people and
investigated by NASA, tin “whiskers “ develop over time between the inner
transistor case and connections inside. This causes hard to fix problems in
the affected equipment. One temporary fix is actually tapping the
transistor itself. I have a number of these little scopes that I parted out
because I could not find the problem. Last night I actually fixed a 321 by
tapping some of the transistors. These scopes have quite a few of the
transistors susceptible to this problem, notably 2N2207 and OC170.

Information on this can be found by reading and following links within the
following documents:

https://nepp.nasa.gov/whisker/anecdote/af114-transistor/index.html


http://www.vintage-radio.com/repair-restore-information/transistor_transistor-faults.html

https://nepp.nasa.gov/whisker/

There is a lot more but this is a good start. I now must go tap some more
transistors.






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