Scanning, Faxing & Copying

When scanning a document with grayscale graphics or color photos, or when copying such items, I get strange wavy streaks on the image. When printing from a computer, these streaks do not appear.

It appears to be electrical related, because the streaks are wavy like there is some kind of interference in the signal.

I purchased the printer from Amazon, and they sent me a replacement but it's also doing the same thing.

Steps I have tried to fix it:

1. Unplugged it from surge protector and plugged it directly into the electrical outlet on the wall.

2. Updated the firmware.

3. Reset the printer by unplugging, holding the power button for 60 seconds, and plugging it back in.

4. Worked on scan settings on the computer (but the problem is with copying too).

5. The problem is not caused by dirt on the scanner, because the lines are not necessarily vertical.

Any ideas? Do the other Officejet Pro models have better scanning and printing quality? Our old 8620 that we used the last 3 years was much better quality with both scanning and printing. Are the new ones just that much worse, or are these flukes? Can anyone that has an 8720 (or any 8700 series) comment on their quality with copying and printing?

Here are a couple examples:

This should be a smooth gradient from medium blue to light blue in the background.The wavy streaked part here should be medium gray.