try the old firmware, and tell if it works.
(Old firmware does not work with all types of mouse, and does not support kvm Switch)
Maybe its a combatible issue. Did you try to reset the contoller and reload driver after boot ?
Did you try a different MAX232 Chip ? Did you check Voltages of the Charge Pump ?
Under Windows 7 you need to manually install the serial logitech mouse driver to get it working.
When the Firmware detects the Mouse the Controller works.
How did you wire to the RS232 Port ? The rx/tx and other signals are crossed in the Schematic,
like a nullmodem wire.
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I'm currently put a list of potential buyer together.
Cost will around 10€ +/- and shipping to your country (Location is Germany).