Amiga 2000 mouse problem

[drewz21]

I've got an A2000HD that I pulled out to clean up and the mouse ports don't seem to work.  The keyboard works fine and I can control the mouse with the keyboard but neither mouse/joystick port seems to do anything.

Any ideas on what I can try?

Floppy works, hard drive works, and everything else seems to work.

[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.

[drewz21]

Well crap.  It's got a ver4.4 systemboard in it.  No type of input from the mouse works.

Are we talking total board replacement or is it something that might be repairable?

Thanks in advance!

[Amiga4k]

Simple test for you. Swap the 8520 CIA chips. U301 has keyboard functions, and U300 has mouse functions. It's a cheap chip to replace, about $8-12 US.

[orange]

@Amiga4k
where can they be found?

[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.

[Amiga4k]

Just out of the depths -- did you plug the mouse in the left port or right. Left should be correct.

Orange,
   The 8520 is a socketed chip, and many places should have them. Here are a few, but can not guarantee in stock.

http://www.webworldinc.com       CIA 8520 Chip: $ 16.95

http://www.softhut.com/        CIA 8520 Chip       $9.95

If not, you know me. I do have a few.

[commodorejohn]

I recently acquired an Amiga 2000 and it's displaying similar symptoms; no mouse movement, but the buttons do work. After looking at this thread, I checked the fuse in question with a multimeter, and sure enough, no continuity. It looks like something I can replace myself, but what kind of fuse is it? (i.e. what would I ask for at my local electronics store?)

[JimS]

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

[commodorejohn]

Okay, none of the electronics stores in my area have anything like that, so it looks like I'll have to order online. Unfortunately, I'm not so familiar with low-level electrical stuff. If 4A turns out to be too low, I assume it'll just blow, but would I be risking anything if it turns out to be too high? Does it matter what voltage it's rated for? Are these about what I'd need?

[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. ;-)

[commodorejohn]

I'd considered doing just that, but Radio Shack said they "don't stock anything that small," and there don't seem to be any other electronics stores in my area that are more than generic consumer gadget wholesalers, even to the extent that Radio Shack is :/

[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.

[commodorejohn]

Hmm. Maybe I'll get a few of each, and if the 3A fuse doesn't work I can always replace it with a 4A fuse.

[JimS]

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