intermittent pico fuse

[maxkracht]

New failure mode, to me at least. I was told this amp was cutting out but everything was working normally when I got it. Had to remove two boards and a snap in power switch to get to the underside with all the components, and found the heater fuse cracked in half. I have seen glass fuses blow and continue to conduct, hadn't seen the pico fuse version where it's just intermittent. Also interesting, to me at least, the bias circuit and low voltage supply share a winding and a fuse. Think I might move the fuse so it bypasses the bias supply...

[maxkracht]

Cut it open, I think the lead came loose from the metal cap causing the end to heat up. The fuse wire was completely intact. Guessing this was a manufacturing error.

[TUBEDUDE]

It might be a public service to identify the manufacturer that fuses the bias voltage.

[xtian]

It might be a public service to identify the manufacturer that fuses the bias voltage.

That looks like the heater circuit to me...

[maxkracht]

Yes, this was the heater fuse that failed. Fusing a bias circuit seems like an odd choice to me, but maybe i'm missing something. Fusing the low voltage supply for the opamps and dsp seems entirely rational, just not together with the bias circuit. I'm replacing all the pico fuses for good measure and moving them to the top of the board so it doesn't take an hour to replace in the future if there's another nuisance fuse failure.

[TUBEDUDE]

Yes, this was the heater fuse that failed. Fusing a bias circuit seems like an odd choice to me, but maybe i'm missing something. Fusing the low voltage supply for the opamps and dsp seems entirely rational, just not together with the bias circuit. I'm replacing all the pico fuses for good measure and moving them to the top of the board so it doesn't take an hour to replace in the future if there's another nuisance fuse failure.

Oops, I was focused on the image and failed to notice the schematic labelling the mfgr.