While I am restoring this lovely AU-717 amplifier, I felt it was worth discussing the infamous Sansui corrosive glue problem.
Most equipment manufactured by Sansui, and others, during a certain period in the 70’s and 80’s will be affected by this nasty, corrosive compound. Its called polychloroprene and it literally eats through components like an acid.
The amplifier I am currently working on is no exception and several parts are so badly damaged that they almost fell off the board. The brown glue was used to hold larger parts firmly to circuit boards and does a good job of that.
However, it seems long-term testing to see what would happen to the parts held down by the brown glue over many years wasn’t done. The result is a large number of problems caused by the glue eating through components.
This corrosive polychloroprene glue will destroy circuit board traces, eat through component legs and even dissolve the parts themselves. Anywhere you find this dark brown glue, you need to remove it carefully from boards and parts. Leave as little remaining as possible remaining. You should also carefully examine the leads of any parts that have been exposed to this compound and look for signs of corrosion. Replace affected parts where necessary.
The amp I am restoring for my customer needs many new parts, some due to damage caused by this corrosive glue. I will also replace other parts that have degraded over time, like some heat-damaged caps on several boards. The following photos depict the nature of the problem in this otherwise pristine Sansui AU-717.