Detailed Answer
Troubleshooting: 1. dead/reversed battery (most common); 2. oxidized battery contacts (clean them); 3. key switch not turned on; 4. battery compartment cover not closed properly (poor contact); 5. internal circuit fault (return to factory). LDER LD series indicator meanings: green = normal, red flashing = low battery, both flashing = pairing mode. Replace the battery first, then check the contacts.
| Battery | Try a new one |
| Contacts | Clean |
| Fault | Return to factory |
Note:Indicator states match the manual for quick fault diagnosis.