My parents gave me their remote that wasn’t working after the grandkids dropped it on the hardwood floor. Taking it apart and checking for broken connections, everything was intact. A little research online indicated the 455khz ceramic resonators used for timing are susceptible to shock and was a likely culprit for drop damage. I checked the local electronics stores but they didn’t carry the part so I ordered 5 pieces on ebay from Asia for $1 (includes shipping). Getting impatient, I then decided to head to the recycling center and ended up finding an older but brand new remote for a camcorder that I was able to salvage the resonator from. The replaced resonator fixed the remote and the resonators I ordered eventually did arrived 8 weeks later.
A good way to help debug problems with remotes is to use a digital camera (smartphone or tablet works as well) to view the pulses coming from the IR LED to confirm your remote is working. Another technique is to use an analog multimeter to see the pulses while probing the voltage at the LED if you don’t have an oscilloscope.
For maintenance, I regularly take remotes apart to clean them since they collect a lot of gunk from sticky fingers. The circuit board gets cleaned with rubbing alcohol while the the plastic case and rubber keypad gets a bath is hot soapy water. Dry it completely before reassembling. Don’t wash the circuit board!!