I have a printer thats printing on one side only. how can i fix this

Unfortunately, 2-sided printing is only available for the Epson L20 when used with the Windows OS. See page 22 of the user guide available here: https://www.epson.com.ph/Ink-Tank-Printers/L-Series/Epson-L120/s/SPT_C11CD76401?review-filter=Mac+OS+X+10.11.x#manuals . The current link to the manual is http://support2.epson.net/manuals/english/ij/l120/pdf/npd4965-00.pdf . You might be able to use the Duplex feature if you install BootCamp and an licensed version of Windows (XP up to WIndows 10). Neither BootCamp or licensed copies of Windows are free.

I wish that I had better news for you.

Cindy Wells

Brother printer not printing double sided correctly
If the Paper Adjustment Lever for 2-sided(Duplex) Printing is not correctly set for the paper size, paper jams may occur and the print will be out of position on the paper. Open the Properties dialog box in the printer driver. ... The printer will print on both sides of the paper automatically.Sep. 2, 2016

Print on both sides of the paper(2-sided/Duplex Printing ...

https://www.google.com/search?q=Brother+Printer+Duplex+Not+Working

The R300 is not capable of double sided printing, it has no duplexer

1. Right side not printing. Rotate round green knob (possible black center) found on right side of printhead assembly clockwise (or if necessary, through entire range) printing at each stop to check, until printing is satisfactory. If not fixed, next step is to do "Burnline Adjustment" as described in Operator's Manual.
2. Left side not printing. Make sure that large green plastic printhead latch on right is pushed firmly toward back of printer while printhead is pressed down, to make positive lockdown of printhead. Try rotating round green knob described in (1) above through entire range, printing at each stop to check. If not fixed, next step is to do "Burnline Adjustment" as described in Operator's Manual.

What you want to do is set the printing properties to duplex printing. To do this, go to Start>Devices and Printers. Select your default printer and right click on it. Click on "Printing Preferences". Place a check in the box that says"Duplex Printing." Click "Apply" then "OK." The printer should now print on both sides of the paper. Please comment if you need additional assistance. Thanks for using Fix Ya.

goto printer property and select 2 side printing .

First check to see if there is anything inside the printer that isn't suppose to be there. Such as coins, buttons, pens ect.

The duplex unit is an OPTIONAL component on that printer.

The only reference to a "two-sided printing module" I could find in relation to an Officejet is on the following web page at HP.com:

Two-sided Printing Overview

Unfortunately, I couldn't find anything specific to Windows Vista that talks about two-sided printing, but my guess is that Vista has yet to support this function for the Officejet 5610. If XP performed two-sided printing without this physical module being installed, it may be that Vista requires it.

The only Vista related web page I found on the 5610's site at HP has to do with downloading a diagnotic software utility:

HP Printing Diagnostic Utility

If all else fails, I'd try downloading and running the utility to see if it'll fix the issue with Vista. Post back your results here. Good luck.

Normally to fix a printer that is printing gibberish, uninstalling and reinstalling the print drivers will fix this issue. Another thing that can contribute to gibberish print is using a USB cable that is too long.

With this particular problem (prints Zen), one solve is to uninstall any Dell toner management software. This is particularly true if you are running Vista and hooked up by USB. To uninstall the toner management software (Vista OS), go to control panel>programs>programs and feature>uninstall a program. From this list choose Dell software, choose a customized uninstall, and then choose anything that has to do with Dell toner management.