Amiga tank mouse fix x-axis

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Repaired a broken Amiga tank mouse ( rev-D A0102200 ).

No X-axis movement. I compared the voltage levels of the IR-phototransistors with the levels of the Y-axis.
There is a difference between the working axis ( Y ) ~460mv and none working axis ( X ) ~240mv.

Voltage level on Y-axis, 460mV

Voltage level on X-axis, 240mV

Replacing IR-phototransistors


There are 2 phototransistors which register the movement of the mouse, a rotory encoder wheel passes the IR light from two IR-Transmitters to the phototransistors. I replaced both phototransistors, so the output voltages that are transmitted to the voltage comparator ( LM339N) will be the same.

Removed phototransistors
New LPT80A’s

After the replacement I measured the voltage levels again and they are significant higher then before.

Volt level on x-axis after replacement phototransistors, 740mV

For the replacement I used two OSRAM LPT80A phototransistors ( datasheet )

Testing time

Hooked the mouse to the Amiga, and it’s working again. So the repair is completed successfully.

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