black page

Looking for some toner cart construction secrets that could explain this behavior. This concerns a problem with a Canon PC330 portable copier. The old cart was beginning to produce lighter copies, so I ordered an "equivalent" E1 replacement but the new cart produces a totally black output...

Hoping someone can diagnose my problem. Just bought a "new" used HP laserjet pro m402n. Everything setup perfectly and it is on the most current firmware. It is configured to print through a network connection and I've purchased two refurbished toner cartridges. When I print a document it...