The Roku Ultra 4800, 4801(LT), and 4802 are near identical devices. The 4801 is a Walmart exclusive brand that lacks a USB port. The 4800 and 4802 are identical units but comes equipped with different remotes. (4800 comes w/ Voice remote, 4802 comes w/Rechargeable remote). Any info you find for one of these devices can be used for configuration with any in this particular line.
Disregard any letters after the model number. These just indicate place of purchase. A 4802R is exactly the same as a 4802X and vice versa.
As to your questions regarding any manuals, there really is no troubleshooting manual. There are online Support Articles at https://support.roku.com/ that give basic troubleshooting and info about the device, including the setup manuals and videos. For detailed troubleshooting, short of actually contacting Roku Support at https://support.roku.com/contactus, most questions are addressed here in the forum by fellow users familiar with these devices.
How to set up your Roku® Ultra - https://support.roku.com/article/223372368
Getting to know your Roku® Ultra - https://support.roku.com/article/360053315174
From the above link, their is a link to the Roku 4802 Quick Start Quide manual that came with the device at https://image.roku.com/c3VwcG9ydC1B/Ultra-4802-QSG-US.pdf
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