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.

"Nutcase Kook"

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.

** 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

On 16/05/2014 07:39, N_Cook wrote:
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.

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