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Microsoft Mouse repair! Need some help!

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First post, by Hezus

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I've been using a Microsoft Serial 2.1A mouse and a PS2 Microsoft Intelli Mouse for a long time with my retro PCs. I find them nice to use and fit the 90's vibe very pleasing. I'd like to use them for the years to come but both mice seem to run into the same issue.

One one axis (the serial one is left to right, the ps2 does it for up/down) it's getting hard to move the mouse pointer carefully without it stuttering or not registering movement. Internally, the mouse movement is tracked with a wheel and a sensor. The sensor detects whenever there's a gap in the wheel and then sends the data accordingly. I suspect that the sensors are starting to wear out and thus create these stutterings.

Here's a pic of the disassembled mouse. The sensor setup is the black block with green/blue dot on top and the plastic block on the opposite side.

cDrFgym.jpg

Does anyone know which type of sensor this is? Is my assesment correct and does it need to be replaced or is something else going on?

Thanks for any help! 😀

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Reply 1 of 3, by wbahnassi

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It could be dirt, or I also suspect something similar to this is happening:

https://m.youtube.com/watch?v=dJgMCd25guY

I fixed an old mouse this way. Kept playing with resistor values until I found the magical one that made the mouse smooth again.

Reply 2 of 3, by Hezus

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wbahnassi wrote on 2023-07-19, 19:20:

It could be dirt, or I also suspect something similar to this is happening:

https://m.youtube.com/watch?v=dJgMCd25guY

I fixed an old mouse this way. Kept playing with resistor values until I found the magical one that made the mouse smooth again.

That's a good reference! It might be related to the resistor values. It's funny how similar the build of this mouse is to the old Commodore mouse. Don't fix what ain't broken, I guess?

quSDH1I.jpg
kUqEtNo.jpg

I've managed to find the datasheet for that chip. Here's the block diagram & pinout:

QLjI6hb.png
pGVHaJV.png

I think there might be some differences in the way the serial port works on a PC as opposed to the Commodore. iirc the signal in the PC's serial varies from -3v to +3v, correct?

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Reply 3 of 3, by Hezus

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Comparing the schematics of the Commodore mouse and the Microsoft board, there seems to be a difference in how the resistors are handled. In the Commodore schematics each direction seems to have its own resistor, so 4 in total. I've tried to map out the routes on the Microsoft PCB:

9ggFJNe.png

So, the large R1 resistor is the same, but it only has one resistor per axis (R10) and (R4). Pins 4-7 are there for the quasi interrupt detection. One axis goes to pin 4-5 and the other to 6-7. Pin 5 and 6 are connected through a resistor to pin 16 and 17. This is where the serial data goes.

The issue with the mouse are careful movements towards the left, but going right is just fine (up and down is fine too). I wonder how this is can be a resistor issue if the same resistor is used for both directions and one of those directions is just fine. Anyone got any other ideas?

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