Epson EcoTank Pro ET-5150 Wireless All-in-One Supertank Printer - Manual (Page 289)

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5. Using the flashlight, check the translucent film shown here for ink smears.
1 Translucent film
2 Print head rail
Caution: Do not touch the print head rail or wipe the grease off of it. You may not be able to print. Do
not touch the white flat cable or ink tubes.