Casio CZ/ VZ/ FZ - Pro Series

I committed a cardinal sin and let my batteries rot inside the backup compartment of my CZ-3000. I couldn't see any damage as it is pretty isolated in there but now having replaced with fresh batteries I can't write to user tone area. It always says the "Protect switch is on" (which it isn't). If I do a system initialization by holding down the power it does write that area with presets. If I take out the batteries again the memory is wiped as it should be. Has anyone seen this before? My CZ-3000 is precious. Can't believe I've been so mean to it.
Its got me thinking about my CZ-1. It doesn't have any battery compartment but presumably that has a battery backup internally that could rot?

Some corrosive gunk will have leaked onto the board and rotted one of the
tracks.  It's no biggie, just find it and link across the affected bit with
some thin wire.

For more information about this sort of thing, search for Korg Polysix
battery repairs - the nicads they used are hellish for it.

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Gordonjcp MM0YEQ