Make mine melamine, part 2
Brad Thompson, Contributing Technical Editor brad@tmworld.com -- Test & Measurement World, 2/1/2009 2:00:00 AM
I received several replies to “Make mine melamine” (“Test Voices,” December 2008/January 2009). A reader who maintains broadcast equipment offers the following comment:
“Search for conductive brown glue and see what we have been fighting for years. Whenever I fix something electronic, that glue becomes the first suspect…. Sony Broadcast VTRs used this glue under passive low-pass video filters that often malfunctioned. After replacing a few filters at $300 each, I investigated and found the glue was conductive. Removing the glue fixed the problems. The filters were never defective. A Sony tech bulletin described it as “chloroprene glue,” but who knows what else was in it.”
Another reader commented, “I briefly worked at a computer case company in Taiwan near the end of 1997. At that time, case vendors—basically metal stamping operators—added value by including a power supply (PS) in each case…. Since the metal stampers had no electrical knowledge, they’d just buy any PS from one of their friends without providing specifications or performing incoming QC testing. This led to quite a few product returns to the US office, which cost a lot of money….”
A Google search for “conductive brown glue” finds more than 100,000 references, some of which mention the glue’s role in various CRT display problems and its use in consumer audio equipment. Searching for “chloroprene adhesive,” Google finds 56,000 references, including one from a Sony division that contains the following cautionary note: “The products…contain chloroprene rubber…. Prolonged standing in a high-temperature environment…may cause thermal dechlorination, possibly resulting in the corrosion of metal parts nearby, or in a loss of insulation resistance. Please be sure to avoid any use of these materials in electronic components that are to be energized electrically to prevent tracking or similar problems.”
As the second reader suggests, given informal procurement processes, it’s possible that a subcontractor used inferior glue to attach components. An archived e-mail note conjectures that “...The plain gummy petroleum glue is ok over time, but [there’s] a problem with a filler/bulking agent used. I agree that it goes brown with age, [so] perhaps it’s a corn flour or vegetative starch filler. I doubt a mineral [filler] like talcum or French chalk would discolor to a very dark brown or become a problem....”
So the filler might yet be melamine.
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