Faulty Toroid?

[Gian]

Hi

I have a Digitech 100W per side stereo amplifier that I use to drive my passive speakers on my kids iMac that they use.

I went overseas and when I got back, the amp wasn't working. I asked what happened. But no one knew anything. Typical. I look inside and the fuse has blown. I replace the fuse and it keeps blowing it.

Anyway, this is what happens:

scenario 1: power goes into the unit, I disconnect the input (primary) to the toroid (in the power supply) and turn on the unit and the fuse DOES NOT blow. Its a 3.15A fuse.

scenario 2: power goes into the unit, I connect the input (primary) to the toroid (in the power supply) and disconnect each of the two (centre tapped) secondaries and when I turn the unit on the fuse DOES blow.

scenario 3: when I connect the secondaries of the toroid to the rest of the circuit the fuse DOES blow.

I measured the primary resistance with a multimeter and it measures around 400ohms.
I measured each of the secondaries and it measures about 2 ohms from each side to the centre tap.

Any thoughts?

[rob]

SLOW BLOW

All toroidal transformers pull a shit load of current on turn on ( depending on where the mains cycle happens to be when the switch is thrown ) A fast blow fuse will blow in this situation.

So you want a 3.15AT fuse. The T stands for time delay or slow blow.

Of course it is possible that the transformer is faulty, but using the correct fuse will allow you to establish this.

[Gian]

Thanks Rob, I'll give that a try.

[Gian]

OK, I put a slow blow fuse in and it blows straight away.

I measured the primary coil and it is 3.3Kohm (240V AC) and each secondary is 1 ohm each (cant measure the secondary voltages but the are supposed to be 23VAC and 14.5VAC). I am not sure if those resistances sound right.

[rob]

if it blows with the secondaries fully disconnected from the power supply, then the transformer is cactus. That resistance of the primary seems way too high, this in itself wouldn't blow the fuse but is indicative that something terminal has happened within the transformer. Perhaps there is a short within or between the windings.

[Gian]

OK, so, instead of chucking the whole thing, should I send the toroid to someone like Harbuch to fix? Or should I try to source a replacement toroid? How would I determine the current rating of the secondary windings?

[rob]

contact the distributer and see if they can supply a replacement