"John Robertson" wrote in message
...
On 2017/03/04 7:17 PM, Phil Allison wrote:

John Robertson wrote:

** That should be "Silver Sulphide" = Ag2S


Do you know what "black leg" corrosion is ?

Commonly seen on the leads of small signal transistors made in Japan in
the 70s. It often results in the device going noisy or failing
completely. Marantz stereo amps were notorious for it.


Can you provide a link to more in depth discussion on your black leg
corrosion? I did a quick search and could only find one reference, and
it merely said watch out for 'black leg corrosion'?


** Not much to be found on the net, but something most service techs have
seen.

Bit like the "yellow glue" problem that has plagued countless items and
still is.


I have run into a lot of Namco branded ICs from Japan, made in the late
70s that have this problem...


** It's got be due to silver plating the leads.


I'm sure they thought that silver plating was a good idea, instead of
planned obsolescence.

My first job was fault finding huge desk calculators that only did the most
basic functions and contained about 200 DTL chips.

Most of the chips had silver plated pins and I never had a fault because of
that - a few chips had gold plated pins, there may have been less than
half-dozen faults because the alloy interface became an insulator (there was
no inherently dodgy RoHS soldering back then).

You could always tell the silver plated ones because the pins were black.
The tinned ones never got past dull grey.