• Code: U4-2
• Description: Over Heat Temp Fail. A temperature of 250°C or higher was detected continuously for 480 ms.
• Remedy: When U4-2 occurs, [NVM 50-20 FSR Reset FuserOverTemp] becomes "1." Run [NVM 50-20 FSR Reset FuserOverTemp] using "0" to reset it. Check the resistance of the Thermistor. There is no open circuit between J601-1 ( P/J601) and J601-2, and the resistance is a minimum of 228k ohms (cold). Y↓N→Replace the Fuser (PL 5.1) . Check the wire between J408 ( P/J408) and P601 ( P/J601). The wire between J408 and P601 is not shorted or open. Y↓N→Repair the wire. Replace the Fuser (PL 5.1) , the LVPS (PL 8.1) , and the AIOC PWB (PL 8.1) in that order.

• Code: U4-3
• Description: FS1 Thermistor Defect. Thermistor FS1 cannot be monitored any more.
• Remedy: Check the condition of the Fuser. The Fuser is installed properly. Y↓N→Install the Fuser properly. Check the resistance of the Thermistor. There is no open circuit between J601-1 ( P/J601) and J601-2, and the resistance is a minimum of 228k ohms (cold). Y↓N→Replace the Fuser (PL 5.1) . Check the wire between J408 ( P/J408) and P601 ( P/J601). The wire is not shorted or open. Y↓N→Repair the wire. Replace the Fuser (PL 5.1) and the AIOC PWB (PL 8.1) in that order.

• Code: U4-9
• Description: Fuser Fan Defect. After the start of Fan Fail Signal monitoring, the signal level was Low not more than 30 times.
• Remedy: Turn the power ON. Visually check the NOHAD Fan (PL 9.2). The NOHAD Fan is rotating. Y↓N→Measure the voltage between the AIOC PWB P405-3 ( P/J405) (+) and GND (-). The voltage is approximately +24VDC. Y↓N→Replace the AIOC PWB (PL 8.1) . Replace the NOHAD Fan (PL 9.2) and the AIOC PWB (PL 8.1) in that order. Measure the voltage between the AIOC PWB P405-2 P/J405 (+) and GND (-). The voltage is 0. Y↓N→Replace the NOHAD Fan (PL 9.2) and the AIOC PWB (PL 8.1) in that order. Replace the AIOC PWB (PL 8.1) .

• Code: U6-2
• Description: RAM Read/Write Check Error. When the AIOC PWB checked RAM read/write at activation, a mismatch of read and write data was detected.
• Remedy: Check each AIOC PWB connector. Each connector is connected securely Y↓N→Connect each connector securely. Turn the power OFF and ON. U6-2 recurs. Y↓N→Completed Replace the AIOC PWB (PL 8.1) .

• Code: U6-3
• Description: NVM Data Defect. • NVM Header data and NVM 3 page data are mismatched. • Or, the NVM Write & Read area is not found. • Or, the NVM or Counter area is full.
• Remedy: Check each AIOC PWB connector. Each connector is connected securely. Y↓N→Connect each connector securely. Turn the power OFF and ON. U6-3 recurs. Y↓N→Completed Replace the AIOC PWB (PL 8.1) .

• Code: U6-4
• Description: NVM Read/Write Cannot Be Executed. • During NVM read/write, the NVM Ack NG state was detected. • Or, during NVM repairs, an NVM write error was detected five times.
• Remedy: Check each AIOC PWB connector. Each connector is connected securely. Y↓N→Connect each connector securely. Turn the power OFF and ON. U6-4 recurs. Y↓N→Completed Replace the AIOC PWB (PL 8.1) .

• Code: U6-5
• Description: CPU Power To Access NVM Is Not Enough. At NVM write, the NVM queue full state was detected.
• Remedy: Execute diagnostics [29-49] to check the ROM version. The ROM is the latest version. Y↓N→Upgrade the ROM to the latest version. Replace the AIOC PWB (PL 8.1) .

• Code: U7-0
• Description: UI Communication TimeOut. At Power ON, the AIOC PWB does not communicate with the User Interface PWB.
• Remedy: Measure each voltage between AIOC PWB J401-1 ( P/J401) (+), J401-2 (+), and GND (-). The voltages are approximately +5VDC. Y↓N→Replace the AIOC PWB (PL 8.1) . Check the wire between J401 ( P/J401) and J710 ( P/J710). The wire is neither shorted nor open. Y↓N→Repair the wire. Replace the User Interface PWB (PL 8.4) and the AIOC PWB (PL 8.1) in that order.