The HP2500 cartridge uses a clear glass window and a LED emitter and receiver to check for toner. Maybe storage conditions or temperature may have affected it.

• 2500等机器的粉仓都有一个透明的小窗口，一个发光二级管的发射器和接受器，用于“监测”碳粉的存量。储存的方式和温度也会影响计数器的工作状态。