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Instruction Manual 5.0 SERVICE 5.1 Enclosure Replacement The Model 20X enclosure should be replaced if the lid threads or conduit threads have been damaged, or if the enclosure has corroded sufficiently that it no longer meets the required NEMA classification. To replace the enclosure follow the electronics board and sensor removal instructions, remove the dam- aged enclosure from its conduit or wall mounting, install a new enclosure and continue the electronics board and sensor assembly replacement instruc- tions. 5.2 Electronics Board Replacement The electronics assembly should be replaced when it is determined that it is unreliable, noisy or cannot be adjusted for calibration. This may occur due to age, corrosion or failed components. To replace the electronics assembly in the Model 20X Series: 1. Confirm that the system power has been removed. 2. Remove the lid of the main enclosure. 3. Disconnect the sensor from the plug on the lower right hand corner of the board. 4. Disconnect power and signal wires from terminal strip TB1 and the wires at T62. 5. Press closed the two plastic holders retaining the electronics board and remove the board. 6. Reverse the preceding steps to install the new electronics board. 7. Restore power and allow a minimum of 30-60 minutes for stabilization before recalibration if the unit was off power for less than 60 minutes. To replace the electronics assembly in the Model 20OX Series: 1. Confirm that the system power has been re- moved. 0 2. Remove unit from mounting surface. 3. Remove the cover of the main enclosure by removing the two small screws on the top and bottom of the enclosure. 4. Disconnect power and signal wires from termi- nal strip T131 and the wires from T132. 5. Remove the two screws retaining the electron- ics board from the back of the enclosure. 6. If you are not replacing the sensor, unplug it from the electronics board. 7. Reverse the preceding steps to install the new electronics board. 8. Restore power and allow a minimum of 30-60 minutes for stabilization before recalibration if the unit was off power for less than 60 minutes. 5.3 Sensor Replacement The gas sensor needs replacement when: - It is no longer possible to obtain correct calibration - The failed sensor alarm (oscillating red/green LED) is on - The sensor output signal is noisy, causing incorrect gas alarms. To replace the sensor on the Model 20X series: 1. Confirm that the system power has been removed. 2. Remove the cover from the main enclosure. 3. Unplug the sensor connector on the lower right hand corner of the electronics board. 4. Unscrew the sensor assembly from the end of the enclosure. 5. Reverse the preceding steps to install the new sensor assembly. 6. Restore power and allow a minimum of 24 hours for stabilization before recalibration. The cali- bration should be re -verified after 6 days of con- tinuous operation. Page: 7 20X/20OX Gas Sensor Modules (08/04)