fuse identification

[gbrower]

Could anyone tell me what amperage and slow/fast blow a F4L250V glass fuse is? Or where I can find the info? Can't seem to get the internet info anywhere.<p>thanks

[philba]

Do you know who makes it? its not a LittleFuse or bussmann number. Just a guess but: 250 V 4A fast blow? What is the voltage and amp rating of the device it's fusing?

[gbrower]

It's fusing a power supply in a home theatre made by Koss Dav2503. I guessed it to be what you said but it blows as soon as power is applied. Something must be wrong with the power supply I guess.

[Dean Huster]

Yes, that a 4A, 250V fuse. With a fuse blower, never blame "weak" fuses. It's always a problem in the circuitry. You're most likely suspects will be output amplifier, rectifier or filter caps, an output amp being most likely.<p>Dean

[jollyrgr]

Check power supply rectifier diodes (bridge rectifier, if present or the four descrete diodes). In some cases there may be a couple different supplies with their own bridge rectifiers.<p>Not finding shorts there, start isolating the power input pins to the power amp ICs. Since you mention that it is a home theater system is it "modular" inside? In other words is the power supply separate from the amp and control circuits? If so, disconnect all sub circuits from the power supply. To save on fuses put a normal 50 watt lightbulb in series with the AC line. If the bulb glows brightly (i.e. normal brightness), the short is still present. You can reconnect the sub circuits one at a time and re-apply power. When the bulb glows brightly, you've found the offending circuit. If the bulb glows without anything connected to the power supply output, the problem is within the supply itself.

[Enzo]

When an audio amplifier blows fuses, it is usually shorted output devices. In your case probably one of those "hockey puck" amplifier chips. After that, shorted rectifiers come up. Everything else is WAAAY down the list.<p>F4A means Fast 4 amps. The alternative is T4A meaning Timed 4 amps. Timed means Slow Blow. 250v means it is suitable for use in the mains fusing. Some fuses are rated for 32v and would not be suited to mains use.