I Have Xerox 5821 Star Copier and it got U6 error. Help me out

Try this link:

Error Codes and Support

U6-1 The main PWB failed checking the ROM.

Shut down and restart the copier. If it appears again U6-1, replace the main PWB.

U6-2 The main PWB failed checking the RAM.

Shut down and restart the copier. If it appears again U6-2, replace the main PWB.

U6-3 and U6-4 The main PWB failed to check the battery MNV (U6-3). Or the main PWB does not properly initialize the NVM (U6-4).

Follow the procedure in the development of memory to initialize the NVM, code 20-96. Shut down and restart the copier.

Try this link:
Xerox WorkCentre M118 Service Manual

Hello, Assuming this error is persistent and a simple reboot will not clear it. This error means that there is an Memory Error. This might be caused by an improper grounding (earthing) of the machine.
To fix this error, in case the problem is not grounding, parts need to be replaced. So I would advise you to book a visit.

A U-6 means the memory on the main board failed.
If the machine is old, the battery on the board is old and not holding the values in the machine.
Replace the main board will correct the problem.
Since it is in the middle deep in the machine you might need to have Xerox repair it for you if they still provide service to this model.
Good luck.

u6 is probably a cover is open or broken check all the covers and doors and make sure they are closed

it need to replace the connector in the toner cartridge

Hi,

The most common explanation for the error 'U4-2' in all the 'Xerox' machines is "Fuser warm up failure occurred". I am very sorry that such a problem has occured for you. It cannot be solved by you, if you are not a qualified technician and without proper tools.

Please do call the nearest service centre for a visit and they will probably solve it in a day. Remember, they need the service manual procedures for solving it properly.

Don't worry, it is a very common problem. But only authorised service people can help you in a good way.

Bye

:)

Have a nice time.

Hi
you havenot installed drum cartridge properly inside the machine or you have installed the drum cartridge of Xerox 5816/5821.
Hope you will do it.

Seems to be something to do with the Ram.

More help HERE