HP 3390 Service Manual - Page 261

2. Use a non-conductive probe to depress the engine-test switch. A single test page prints. CAUTION Use a non-conductive probe to depress the engine test switch. Inserting a conductive probe to depress the switch can damage the all-in-one. NOTE The formatter must be connected to the ECU in order to perform an engine test. Otherwise, the all-in-one does not print. Figure 6-46 Engine test switch Half self-test functional check The print process can be subdivided into the following stages: ● Image formation stage (charges the drum and writes a latent image to the drum with the laser) ● Development stage (forms a toner image on the drum) ● Transfer stage (transfers the image to the media) ● Cleaning stage (removes excess toner from the drum) ● Fusing stage (applies heat and pressure to the media to make the image permanent) To perform a half self-test check The purpose of the half self-test check is to determine which process is malfunctioning. 1. Print a configuration page. 2. Open the print cartridge access door after the paper advances halfway through the all-in-one (approximately five seconds after the motor begins rotating). The leading edge of the paper should have advanced past the print cartridge. 3. Remove the print cartridge. 4. Open the print cartridge drum shield to view the drum surface. If a dark and distinct toner image is present on the drum surface, assume that the first two functions of the electrophotographic process ENWW Functional checks 239