Horizontal colored lines through grayscale printed photos

First, are you running low on those ink colors? If not, possibly print cartridges need cleaning. If printer has separate print heads, they made need cleaning.
Lastly, print head(s) may need replacement.

The printhead has either become too clogged to flush out with with the internal cleaning operation (which uses a LOT of ink), OR, the nozzles are not firing. If after several cleaning operations there is still no significant improvement, you will need to replace the print head. I see this frequently with Canon and Epson, and Brother inkjet printers. Usually, it is due to leaving the printer idle for too long, or removing a cartridge and not replacing it right away. The air gets to the residual puddle of ink in the head and dries it.

You can find the replacement print head by Google searching "MP830 print head". Prices can vary from around $70 - $90. Changing it out is fairly simple. You only need to lift a lever that holds the head in place. Make certain that it is squarely seated, and then run a few pages of a color document, or do a couple of standard cleaning operations to "prime" the head.

Make sure the hed is NEW and not used or "refurbished". Here is one source on eBay that sells it for $78.00:

http://compare.ebay.com/like/330643273134?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar&_lwgsi=y

If cartridge is good, prime and allign, remove cartridge and clean copper contacts with contact cleaner, if all fails replace printer.

You need a new printhead,QY6-0049-000, around $50.00.

Selecting grayscale only will also make use of your color. when u select grayscale, look under the print options and select black cartridge only and for more economic printing, use fast draft or draft printing.

Are you sure your ink is not on the verge of finishing? Try changing the colour ink and print again. Sometimes I take the cartridge out, shake the ink down just in the same flashing motion as I do my pen, then replace it. You may try that.

Replacing the print head
The print head may need replacing if, after all print head and ink tank troubleshooting has been performed:

• The nozzle test appears broken or to have horizontal white streaks.
  
• One or more of the colors is missing from the Nozzle Test.
  
• The colors are incorrect on the Nozzle Test.
  
• A print head error is indicated on the unit.
  
• The printer powers off when the print head is installed.

I hope it helps!!!

remove the cartridges and the printhead
do a deep clean by pressing menu>clean printhead
see if it will make a difference then also check your ink levels..

Replace the print head, and all should be just fine.

it could be a faulty printer head in the printer or purged unit not work correctly to clean the heads. you need to do a deep head clean then try printer head tested again. may need to do this a couple of time. still have problems get a new printer head for the printer.