How to merge firmware from an HP printer, fix a few bits and upload it back?

Question

Do it yourself

Good afternoon everyone.
I have an old HP PSC 2353 printer.
After an unsuccessful download of the firmware update, a part of the serial number was rubbed off by the official firmware, more precisely, the serial number became several bytes longer.
Because of this, I sometimes catch lulz.
How I found out: through the service menu I printed out the contents of the memory (nvm) of the device, after that everything became obvious :)
The problem is that the service menu does not allow you to remove characters from the serial number, you can change it or add missing numbers.
Thanks in advance!

Answer 1

1) I hope you tried to reload the firmware?
2) I don’t know much about hardware, but I can advise you this algorithm: find out (on your own or google it) what chip the printer uses and what connectors are on the board with it (JTag for example) and already dance from it.
3) And if it's not a secret, why do you need it? Critical? Or for yourself?

Answer 2

nvm is not a firmware. This is the zone of the eeprom chip area (if the printer is old enough), or several flash pages with an anti-abrasion algorithm. Most of the pieces of iron do not touch the nvm zone when updating the firmware, which is why the problems begin. The new firmware version may not work with the old nvm.