Dell 2355 Mono Laser User Manual page 250

With a dry and lint-free cloth, wipe away any dust and spilled toner from the toner
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cartridge area and the toner cartridge cavity.
CAUTION:
Do not touch the transfer roller inside the printer. Oil from your fingers may cause
print quality problems.
Locate the long strip of glass Laser Scanning Unit (LSU) inside the top of the cartridge
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compartment, and gently swab the glass to see if dirt turns the white cotton black.
transfer roller
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