Amiga 2000 mouse problem

[JimS]

Do the buttons on the mouse work?
The mouse gets 5v power from the center two pins on the bottom row of the connector. There's a fuse in the rev 6 motherboard that protects the port. If that blows, the mouse movement won't work, but the buttons will, since they are just switches.  On older motherboards, it usually fries a trace.

[JimS]

It should be repairable.. the burned power traces (if that's what it is) can be patched with wire. But it sounds like a different problem, since you say the mouse buttons don't work either. Those go thru Paula.

The motion signals go thru U202 (a chip) before they get to the 8520s. I've seen that chip fail. It's not socketed, so you're talking serious business there. :-)

I've also seen the screw that holds the motherboard to the frame right at the mouse port short something out if it's too tight on at least 2 different machines...

Oh yeah, for just about any problem, it doesn't hurt to give all the socketed chips a thumb-press to make sure they're all seated properly.

[JimS]

It's called a "pico fuse". My schematics don't have the rating, but I believe it was 4A

[JimS]

Well, if it's too high, you'd be risking your protection, and probably damage a trace on the motherboard. That's what the pre rev 6 motherboards did. Personally, I was kinda surprised the fuse was that large... I couldn't imagine drawing 4 amps through the joystick port... but it's for short circuit protection, if something gets plugged in wrong.

We're only talking 5v here... The rated voltage is what's not going to arc across the gap if the fuse opens. You don't want to get too extreme, but 120v fuses should be OK. Those fuses from ebay should work. Of course you could always wire in a stock fuse to the stubs of the blown one, MacGuyver style. ;-)

[JimS]

I did some more looking around. The 3000 service manual lists the fuse at 3A..  The 2000 manual just says "fuse".  
It has the same Commodore part number as the 2000 fuse, so it must be the same thing. I'm sure Radio Shack doesn't stock the pico fuses... but they can surprise you sometimes. ;-) I once bought a PLCC chip puller from them.
I think we ordered ours from Digikey, back when I was a service guy.

[JimS]

Can't hurt to have spares around, but I'd stick with the 3A.

[JimS]

Great! glad to be of help