Yamaha PSR-4500 / X4500 keyboard memory pack? (+ROM dump)

[shakalnokturn]

After catching this early '90s synth in the dumpster, spending many hours cleaning all key contacts, washing the sediments of what looked like a layer of barn dust, cobwebs and animal fur with a high pressure cleaner I have a working keyboard.

The upper keys panel with all the synthesiser adjustments is badly warped and some of the screw posts beneath are breaking due to the PCB's pushing them sideways but I can't see what can be done about that.

Anyway attached a dump of the ROM in case it's of use to anyone.

I would be interested in a service manual and any technical information on the cartridges that fit the "PACK" expansion slot.