exxos's Atari, Amiga & retro forum

Hello, sorry to drop with a help request as my first post, but I'm an the end of my knowledge with this.

I've got a standard official mouse a problem, left and right both produce a left movement, and up and down only produces an up movement.

I've reflowed the port, and checked that I have continuity on each pin, went from the next nearest points on the pcb to be sure.

I'm new to the ST, so I dont have much in the way of alternative parts, but I do have a beaten up joystick that I was able to see down and right movement from when in the mouse port.

Replaced both the caps in the mouse, and gave it an ipa bath, as well as scrubbed the rollers and blown all the dust out of the optic wheels. It's barely been used in its life, so didnt seem worth risking breaking the ball housing trying to remove the wheels as it was pretty clean to start with.

I've got a multimeter, a basic knowledge, and a will to learn :) would anybody be able to help with where to look next please?

It may be that the optical sensors are slightly out of line, so try adjusting them, ie bending a little one way or the other.

Bad mouse cable ? Pretty common fault..

Here is a page that might help you.


One of your Xs and Ys is not working. You can test if voltage is arriving from the mouse port to the connector in the mouse. SL1 to SL3 are three different connection variations that you might have. The cable is also sometimes soldered in without a connector. Ignore what it says about Laser and Bluetooth on the document, it is irrelevant.

Have you checked the cable continuity? The cables do often fail because the wires work harden and break due to the mouse movement. This can also cause intermittent operation but as you have a multimeter you can easily test with that in continuity mode. When testing you should wiggle the cable to try and force the fault.

Oh wow, loads of suggestions!

Yes, I do seem to have continuity, and I sensors seem well seated although there is a small amount of vertical movement in each wheel, maybe 0.2mm, which I'll fiddle with shortly to see if it's pushing it out of alignment, and that diagram is super useful, if wiggling the wheels doesn't help I'll check the voltages on the pins.

curlypaul wrote: 11 Apr 2021 10:32 Oh wow, loads of suggestions!

That's what we're here for :)

Hmmm, got +5v on all the pins, now I know which is which I've also traced them back and checked the joints further along and given the cables and optics a good wiggle. No dice.

I think I need to dismantle the keyboard again and take a look at that chip next to the ports.

What's the chip on the mouse board? A hex converter? Any way that I can check that's working?

if you had, or could obtain, a known working 2nd mouse, it would go a long
ways towards ruling things out... Just sayin'... :)

Darklord wrote: 11 Apr 2021 15:44 if you had, or could obtain, a known working 2nd mouse, it would go a long
ways towards ruling things out... Just sayin'... :)

Ye, I could do with a a supply of parts and accessories, bit spent out atm with the STE itself and a pile of floppy drives. End of month I'll get a cap kit and probably another mouse if I've not figured it out by then.