A friend of a friend asked me about some mixer-amp, make unknown. It works fine but every now and they see a blue flash through vent holes. Presumably before the reservoir caps and a break at mains volts, but what? A green flash from a seriously overloaded fuse rupturing, but that would be one-off, but what could give a blue flash ?
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Bad connection, arc-over, family of ants walking across the line. :)
Sorry, this is the sort of thing you'll have to check out for yourself!
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At this point, that's a bit like saying "I have a friend that has some kind of vehicle with some wheels on, and sometimes it rattles. Anyone got any thoughts on what it might be ?"
Do we even know if it is valve or semiconductor ? Valve flashovers can give a pretty good blue flash without too much interuption to operation. I would have thought that any flashover big enough to be seen on a semiconductor amp, even at the mains end of things, would be associated with other (audible) problems ...
Arfa
Most likely a dry jointed/fractured leg on an Inrush current thermistor or dry joint on the mains fuse holder. Why don't you have a look, should be easy to spot. This will be quicker than spending days pondering the problem.
Gareth.
The color of an ARC is generally unimportant. The voltage of the arc, the gas mixture near the arc and any contamination and the total charge transfreerd all play a part in the color. Yellow to blue white is normal, green indicates vaporized metal or other contaminant, red is fire or hot wire not an arc typically.
What is important would be where the arc occurs. Usually once arcing starts occuring, a component has critically failed. There are very few non destructive failure modes that involve arcing.
Do you smell anything when it flashes. Acrid smoke or just ozone?
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