Plantower laser counters may need replacing for various reasons including age, contamination inside the device or simply failing after a long time in service.
Here you can purchase replacement particle detectors. They come in pairs for the PA-II series devices with a plastic component to aid in locating supporting parts.
All Plantower laser counters have been pre-tested in PurpleAir test chambers.
NOTE: Please be sure to select the correct set for your device. - Each type has different connectors or mounting methods. - The images can help identify what you have.