Try to find a Mr Backup z64 with HW2 or HW3 both versions support 256m type roms,unfortunately HW1 only supports 128m type memory.
When a z64 is first powered up it will go through a boot up sequence ...
I have tried to explain the fault briefly without upsetting the person who sold me the ram.
The ram was exchanged from a guy who is well known in the UK for selling retro copier/consol ...
The opriginal DPF 24m ram boards had a 50 Pins type connector,and
there was 6 ICs labelled NEC Japan 424800-70
The guy that I swapped was convinced it would work as mine worked in hi ...