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Yamaha EMX66M mixer-amp

Arcing/sparking wiring/mains-outlet at a venue. Lead to vaporised and neat silvery metal condensed ring and then black deposit in 4A(T) internal mains fuse, presumably something like 50A to do that. I've had full 240V on the isolated mains Tx and nothing obviously awry DVM-D&R cold testing the amp. I intend replacing the 0.1uF yellow block polycarbonate? cap across the primary and doing an autopsy on it. Hopefully there will be an obvious patch of spark eroded metalisation inside it. Anything else to consider,assuming the PA is ok, I may add a NTC in line as a toroidal TX, not included in the design.

Reply to
N_Cook
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"Nutcase Kook"

** No problem for a large toroidal to draw 50A surge current.

That Yamaha has a 400 or 500 VA job inside and no soft start system.

Measure the primary ohms and divide that number into 240 - gives you a close approximation to the max possible surge current at switch on.

With an intermittent AC supply connection, max sized surges are guaranteed.

Just replace the fuse - add a 5ohm NTC if you like.

.... Phil

Reply to
Phil Allison

X2 275V ac ,marked GPF FXK, cap. 2.24m of foil unwound. Loss of metal "healed" mainly near core and at the outside which was more like heat damage as stuck together in that area. Liked to have seen more dramatic damage but in the absence of anything else being found then perhaps that cap shorted, very short duration, 10 to 50 amps

Reply to
N_Cook

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