MB-02+ modification - 28C256
This is modification of MB-02+ to use 28c256 instead of EPROM. It will allow you to flash bootloader anytime you want, directly in your MB-02+.
You will need 28c256, some wires, standard tools, flash utility and bootloader binary.
Here is the guide:
1. copy the flash utility and bootloader binary onto diskette, disassembly MB-02+, take out battery and SRAM
2. cut the track inside SRAM socket, it's A15 heading to EPROM socket, it's no longer needed (photo 1)
3. cut the track between EPROM and SRAM sockets, it's A14 and it heads to EPROM socket, we have to reroute it (photo 2)
4. connect wires underside, /WE from SRAM to pin 27 of EPROM socket, A14 from SRAM to pin 1 of EPROM socket (photo 3)
5. put the SRAM & battery back, connect MB-02+ to Speccy and let BSDOS boot from FDD
6. turn off Speccy and MB-02+, remove EPROM
7. move two switches near EPROM and SRAM sockets to other position (photo 4)
8. put the 28c256 to EPROM socket
9. turn on MB-02+ and Speccy (it won't boot), press NMI, press E, load and run flash utility and flash bootloader
10. if all went ok, you can reset your Speccy and test the new EEPROM.
You can use LMN's flash utility for 29c256, it's compatible with most 28c256's. I made new slower flash utility as alternative, if LMN's utility is not working with your 28c256.
Files: Flash Utility by LMN (with standard bootloader), Flash Utility by me (just utility, without any bootloader).
/WE to pin 27, A14 to pin 1.