Brother HL-4200CN Service Manual page 353

1.1.1 When Controller Board (ESS) is replaced
Take the EEPROM (U8) out of the Controller Board, then put it in the new U8
on Controller Board.
Take out the NIC EXCORD ASSY, then put it on the new Controller Board.
1.1.2 When MCU PWBA is replaced
When you replace MCU PWBA, you must temporary save NV-RAM data in EEPROM of
Controller Board.
1. Turn the power on while pressing the [↑] and [↓] buttons together.
2. Enter the password.
(Password; Press the [ ↓ ] button twice and Form Feed/Set button).
3. Select [CE Maintenance / IOT Diag] with the [↑] and [↓] button, and press the [Set]
button.
4. Select [IOT Diag / Digital Input] with the [↑] or [↓] button and press the [Set] button.
5. Select [NVM Settings / NVM Save] and press the [Set] button.
6. Press the [Set] button to copy the MCU NV-RAM data to ESS NV-RAM.
7. Replace the MCU PWBA.
8. Turn the power on while pressing [↑] and [↓] buttons together.
9. Enter the password.
(Password; Press the [ ↓ ] button twice and the [Form Feed/Set] button).
10. Select [CE Maintenance / IOT Diag] with the [↑] or [↓] button, and press the [Set]
button.
11. Select [IOT Diag / Digital Input] with [↑] or [↓] button and press the [Set] button.
12. Select [NVM Settings / NVM Load] and press the [Set] button.
13. Press the [Set] button to copy the original MCU NV-RAM data to the new MCU
NV-RAM.