Wiebe Cazemier wrote:
Hi,

A friend of mine is trying to repair an active woofer of a speaker set, which
started to blow out the primary fuse suddenly. The problem would appear to be
in the torroidal transformer, because even when nothing is connected, the fuse
blows. We decided to be stupid and put in a 2A instead of 1A fuse. It didn't
blow, and the primary current was only 20 mA. All secondary voltages were
normal. (two assymetric outputs, and one symmetric with center tap).

So, it would appear the inrush current is very high. But, because the device
worked normally in the past, it would appear that the inrush current suddenly
increased. Is this possible? To be more precise, is this possible when all the
secondary voltages are normal? If so, how?

Thanks in advance.

Apart from the slow/fast blow advice given elsewhere, check that the
mounting bolt etc for the toroidal isn't causing a 'shorted turn' by
touching the case on both sides.....if the case is metal then any bolt
through the middle of the toroid must only connect with the case on one
side.

Phil.