Mouse Problems

[AMC258]

Never messed with an A4000 but I know on other big box Amigas, if you unplug peripherals with the power on, you blow fuses.  The mouse port is especially susceptible to this.  Don't complain, it's a great feature.  It really does protect the motherboard.  You'll have to check schematics to find the fuse, or, put a shunt across the fuses one at a time until your mouse starts working.  Be careful though!  And, you could check the fuses with a multimeter but DON'T.  Not unless you have already desoldered them from the motherboard.

Okay, sorry, I didn't read all the way.  If you can right click, the fuse is good.  Then I'd assume you have a bad cable.

[AMC258]

Why not? I've never had a problem testing them with a VMM/DMM.

If the fuse is open, you are not measuring the fuse anymore, you're measuring some part of the motherboard.  This may give a false reading.  Also, then you are forcing whatever current from your multimeter through some part of the motherboard, which in most cases you can get away with, but it's bad practice.

[AMC258]

Sorry for the late reply, I totally missed this way back then.  I only found this accidentally in a search engine!

Here's the best solution:  Power up, and measure *voltage* across the fuse.  If you have 0V, the fuse is good.  If you have >0V, the fuse is no good.  That is the safest possible way to check the fuse in circuit.

Also, if you have an ammeter, you can measure the current in the circuit, across an open fuse.  If you measure more current than the fuse rating, IMMEDIATELY remove the ammeter from the circuit, or remove the power from the system.  At this point, you know that the fuse blew for a reason and you get to search out the fault.  If nothing else it saves you blowing another fuse for nothing.  Just don't leave the ammeter in the circuit like that for too long or you will fry whatever it was the fuse was supposed to be protecting.