HP LaserJet M9040/M9050 Service Manual - Page 157

new, the DC controller sends the open signal to the drum motor. The drum motor rotates in reverse to roll up the toner seal, and then, after a short time, the DC controller turns off the open signal. The DC controller also monitors the presence of a print cartridge. When a print cartridge is inserted, the DC controller checks toner seal status as a signal that the print cartridge is present. Toner level detection The print cartridge includes a plate antenna and a flat antenna to enable the DC controller to detect toner-level. Whenever the power is turned on, a door cover is closed, or a print operation is performed, the DC controller sets the developing bias signal, and the developing AC bias circuit sends a signal to the toner level circuit 1 and to the developing cylinder. This causes the plate antenna to return the output value to the toner level circuit 1. The toner level circuit 1 compares the two signals and sends the results to the DC controller as the toner level detection signal. At the same time, the DC controller turns on the frequency output signal to output the reference frequency to the flat antenna. This causes the flat antenna to return the output value to the toner level circuit 2. The toner level circuit 2 compares the two signals and sends the results to the DC controller as a toner level percentage, which is accurate within 1%. The DC controller reports the result to the formatter. ENWW Image formation system 139