Z80 Code Debugging for Custom Hardware

I'm looking for an experienced Z80 programmer to help me make some minor fixes running on my custom Z80 hardware - which is performing measurement PAV functions like Vrms, Vpk, Vin-phase ratios, fundamental etc. The first task is to resurrect our assembler-complier and create a hex file - identical to the version already have, if these stars align, then its a good start. Next task is to ensure the interface switch (menu item), can be fixed so Serial USB (Max232 driver UM232) or GPIB IEEE.488 can be selected. There is a menu option, presently it does not change the selected interface work (but it did work!).

Key Requirements:
- Extensive experience with Z80 assembly language
- Organised approach
- Prior work with debugging embedded systems
- Ability to understand and interpret detailed technical documentation and schematics

I can provide comprehensive documentation about the hardware and the software. Please include your experience with Z80 and embedded systems in your bid.