What type of programmers are you use to flash the chips?
Is it possible to program it with an Arduino or AVR JTAG USB emulator Debugger download AVR JTAG ICE Download Programmer atmega?
Do these chips have some JTAG headers on board which can be soldered in?
Is there any other way to program old firmware to this printer without disassembling it? Through USB or the SDcard slot?
Thanks