I have a Epson V37 scanner and just noticed it makes a vertical rainbow. Is it broken?

http://www.mediafire.com/view/vy5xlgj2xfi4rvj/epson_v37_rainbow.png

it could be a smudge in that section, if you see it is a vertical, it means the smudge is on that part of the sensor. The sensor run vertically, hence, you see a vertical line.

Smudge means water, or something that break lights into 7 color, making a rainbow effect.

It exists on the entire image...

http://www.mediafire.com/view/5kb1sv8bmzsdp07/epson_v37_rainbow2.png

in that case, then it could be your sensor is having problem, or the connection between your sensor and the printer has problem. The line shows either seems to be noise. Noise means something isn't right with the image sensor

Nothing you can do about it. Feel free to take it a part and try to clean it as the last resort.

Don't worry about it, I doubt you ever notice the rainbow on normal adjustment settings. It's simply a part of many low end scanners.

I got a Brother MFC 6920DW scanner/printer. The scanner is large format 11x17 or A3. Great for anything past A4/Letter size. $229 USD, so quite the bargain. The other nice part, it's wifi and I don't need cables. Vuescan Pro communicates smoothly with it and Photoshop.

There a section of it in the first top four inches that lays a horizontal streak across the scan. It's under warranty, so if I get time, I'll take it to a nearby service center.
I can avoid it for now.

I'm going to post something from Masamune Shirow's Pieces 9, so everyone has an idea what it does.

Are there other A3/11 x 17s below $300 that do a good job?

The Epson GT-15000 and similar like the Epson 1640XL are over a grand retail price, but can be found used on ebay for $200-300 if you watch for them enough.