rebuilt mouse doesn't work properly

Hello,

I'm building a tachometer form my robot out of old PS/2 mouse. After burning the contacts on several of those I've decided to solder the components on a more durable pcb board.

http://mjolnir.lille.inria.fr/turbotouch/lagmeter/datasheet_ADNS2610.pdf

this is the link to the datasheet for the said mouse. soldering mine I've left out the buttons and encoder for the mouse wheel.

This datasheet shows the one transistor in it as PNP, however in the actual mouse there was a W06 transistor, which turned out to be a NPN one, so i also used a NPN transistor. These were all the deviations I've made from the original schematic.

I've used a code that I've got off the internet and I know that there's no problem with the code since it allready had my untampered mouse working exactly how I wanted it. It's supposed to show coordinates of the mouse relative to the starting point. However now it continuosly increases the value of both axis simultanuasly, as if it was moving in 45 degree angle, while actually standing still.

So I was hoping one you could tell me, what could be possible causes for this.

Please and Thank You.