Many thanks for the dump, highly appreciated indeed !
I flashed it on my dual banked FX model and it seems to work just fine.
It doesn't crash like the previous bad dump we had when editing/deleting some cheat codes.
Get attached file and extract its content into your X-Killer folder:
"Xploder FX (Germany) r4.50 PRO 1999-10-25.exe"
This is your rom dump backup installer.
"Xplorer FX (England) r4.52 PRO 1999-11-22.exe"
This is the latest UK rom installer in case you want it (currently set to PAL).
"no$psx bios v2.0.exe"
This is Nocash BIOS Expansion ROM Installer
"xrun_1FF.bin"
This file is needed for X-Killer to upload exe on your cartridge.
If you want to flash your backup or the UK rom, do the following:
Run X-Killer as administrator then:
Tools -> Other -> Upload PSX-EXE -> Select your backup.exe or the UK rom.exe -> Open
Upload should start and when complete you should get Nocash's flasher to boot.
Follow on screen infos.
As long as you have either your rom dump or the UK rom flashed you can still use X-Killer to switch from one to the other.
If you want to flash Nocash's BIOS rom, do the following:
Run X-Killer as administrator then:
Tools -> Other -> Upload PSX-EXE -> Select "no$psx bios v2.0.exe" -> Open
Upload should start and when complete you should get Nocash's flasher to boot.
Follow on screen infos.
WARNING
Once you have Nocash Bios rom flashed you won't be able to use X-Killer anymore to revert.
You'll be able to use
no$psx instead but it will require
you to first perform this simple 1 wire mod to your cartridge.
Just follow Shadow's pictures to get the solder points (the switch is optional).
Usage:
no$psx-> "Utility" -> "Upload to PSX" to send the provided executable(s).
This should cover all your needs.

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