08-01-2016, 05:01 PM
Those Japanese ones can suffer from some sort of growth/migration problem, a thin conductive film starts around the center lead and spreads to the others over time, I first discovered the problem back in the mid '70's whilst working for Sony (service department) the guys were having real problems tracking down some intermittant faults such as general noise, crackling, rustling noises etc or sometimes complete stage failure, after a fair bit of a determined attempt I traced the problem to that as described above.
Gently stroking or rocking the device or heating the leads usually made the symptoms worse or stopped the symptoms altogether, sometimes tapping the PC board would have the same effect which often led service engineers to think it was a traditional dry joint, which it wasn't, even though it manifested itself as such.
The problem was found in both Sony and Hitachi branded transistors of various package styles, and with the rectangular ones in all the usual colours eg: black, green and brown, the conductive film can be spotted with a sharp eye or a magnifying lens, it has a semi iridescent look to it.
Lawrence.
Gently stroking or rocking the device or heating the leads usually made the symptoms worse or stopped the symptoms altogether, sometimes tapping the PC board would have the same effect which often led service engineers to think it was a traditional dry joint, which it wasn't, even though it manifested itself as such.
The problem was found in both Sony and Hitachi branded transistors of various package styles, and with the rectangular ones in all the usual colours eg: black, green and brown, the conductive film can be spotted with a sharp eye or a magnifying lens, it has a semi iridescent look to it.
Lawrence.
