Why are manufacturers still using that crappy yellow glue on circuit boards? You often see it securing large components such as electrolytics, board mounted transformers, and coils. When the glue turns from yellow to brown it becomes conductive. I don't know if heat or current or the combination of both cause it to change, but I've had computer monitors and VCR's malfunction because of it.
My latest experience is with a set of computer speakers--Boston Acoustics BA735. When I got them the volume was very low and there was a fairly loud 60hz hum coming from the subwoofer. The amplifier pc board inside the subwoofer has all the jacks mounted on one edge--power, din socket for the satellites, digital in, analog in, and a bass level pot. All these jacks had a liberal amount of this yellow glue poured between and behind them. Unfortunately this stuff was covering many surface mounted devices as well as a couple of electrolytics. Parts of it had turned dark brown and brittle. I scraped a lot of it using a serrated plastic knife (McDonald's) and carefully pryed away smaller bits using a dental pick. I had to desolder the din socket, digital in jack and caps to get some of it. After putting it all back together, the speakers sound perfect!
I guess the only reason the manufacturers still use this glue is because it's dirt cheap. They don't seem to care that it will cause the device to malfunction 5 years down the road. Silicon RTV would work so much better.