Recovery Guide for Casio FX-5800P Calculator

In rare cases, the FX-5800P calculator may experience firmware corruption, displaying ROM!!!!! on startup. Here's a comprehensive guide to recover your calculator:

1. Remove all batteries from the calculator
2. Leave the calculator without batteries for at least 1 hour (some users report success with this simple step)
3. Reinstall the batteries and turn on the calculator
4. If the calculator still displays ROM!!!!!, proceed to the firmware recovery method.

Firmware Recovery Process

You'll need:

• Another properly functioning FX-5800P calculator
• A 3-pin data cable to connect both calculators

WARNING: The malfunctioning calculator must ALWAYS be set to OS UP Recv and the working calculator to OS UP Send. Reversing these roles will damage your working calculator.

WARNING: This will erase all data in the WORKING calculator, so back up any important information before proceeding.

On the Working FX-5800P (SENDER):

1. Simultaneously press AC/ON + MODE + 7 keys.
   The screen will display DIAGNOSTIC MODE, Factory use only.
2. Press the ← key, then press 9.
   
3. Press 2 to select OS UP Send.

On the Malfunctioning FX-5800P (RECEIVER):

1. Press the FILE key.

2. Select OS UP Recv.

After the transfer completes, the malfunctioning calculator should be working fine again.