Here is the procedure from the notes I have. I have never used this before, but for my Meldas 50M a similar procedure worked when I had to restore it 7 or 8 years ago. Hope it helps you.
500 Series
When replacing a Main CPU (QX-611-1) board on an M520 controller you must replace the EEPROM on the new board with the one from the old board. Then, you must clear the RAM. The procedure for this is:
******** BEFORE YOU START, WRITE DOWN AND SAVE ALL COMMUNICATION PARAMETERS!!! FAILURE TO DO THIS WILL MAKE IT VERY DIFFICULT TO RELOAD THE CONTROLLER!!!****
ALSO IF YOU REPLACE THE BOARD, MAKE SURE YOU RECONNECT THE CSH21 CABLE.
OTHERWISE YOU WILL HAVE A Y03 AMP UNEQUIPPED ALARM.
This is the same procedure to initialize the memory.
1. Save all RAM data to an external device. (Programs,Tool,Parameters)
2. Turn the NC off.
3. Set SW1 and SW3 on. (Move to the right)
4. Turn the NC on.
5. Wait for the green LED on the CPU to turn on.
6. Turn the power off.
7. Place SW1 and SW3 in their normal position. (Off)
8. Format the control.
The procedure for formatting is:
1. Load the Machine Parameters
2. Press the ALARM/DIAGN button.
3. Press the PLC-I/F soft key.
4. At the DEVICE prompt type 758. At the MODE prompt type S.
5. Press the INPUT/CALC button. (The prompts will disappear.)
6. Go to the I/O page and load the Parameters.#(3) INPUT/CALC.
7. Cycle control power.
8. Access the Machine Parameters #(1001) ( ) (M) TOOL/PARAM
9. The BASE Parameters will be displayed.
10. Scroll to page 6/8.
11. Set #6 fix_P to 1.
12. Go to the Data I/O screen.
13. Select ERASE.
14. Move the cursor to the right once and type FORMAT.
15. Press the INPUT/CALC button.
16. FORMAT COMPLETED should be displayed.
17. Go to the Data Input screen and enter #4.
18. Press the INPUT/CALC button.
19. This should load all of the fixed (canned) cycles.
20. Re-Load all Parameters, Tool Data, and Programs.
21. Go to the Machine Parameters (BASE).
22. Go to page 7/8.
23. Set #32 e2rom to zero.
24. Press the INPUT/CALC button.
25. Writing is done when "EEPROM WRITING" goes off.