The iconic image of the American farmer is the man or woman who works the land, milks cows and is self-reliant enough to fix the tractor. But like a lot of mechanical items, tractors are increasingly run by computer software. Now, farmers are hitting up against an obscure provision of copyright law that makes it illegal to repair machinery run by software.

Take Dave Alford. He fits that image of the iconic farmer.

"I do farming on the family ranch," says Alford, standing on a piece of grassy earth with a white barn behind him. "I've been farming for the past 30 years and obviously my family much before that."

Alford wears a blue baseball cap with a farm supply company logo across the top, a plaid shirt, bluejeans and work boots. As Alford and I walk over to see one of his newer tractors we pass what looks like a graveyard of rusty old ones.

Alford says he keeps the old ones around, "Just because I'm a farmer. You keep thinking, well, maybe I'll make this one work someday."

Alford considers himself a small farmer — he's got 1,000 acres in San Luis Obispo along the central coast of California where he grows snow peas, garbanzo beans, hay and seed crops. But he jokes that he tells his friends he's a mechanic.

"You spend so much of your time in agriculture fixing things," Alford says. "I'm of a size that it's more economically beneficial to me to fix as much stuff as I can myself."

But that's been getting a lot harder to do.

Alford and I sit in the air conditioned enclosed cabin of his John Deere 8520T tractor. In the cabin are little computer screens that monitor the engine.

"So I can monitor, for example, what my hydraulics are doing that's running the implement behind me," Alford says. "I can monitor the regular standard things in an engine."

And the little computer screen lets him know when something is wrong. Unfortunately, Alford isn't allowed to fix it. John Deere has a digital lock on the software that runs his tractor. And it won't give him the key.

If something goes wrong with one of his tractors Alford has to take it to an authorized John Deere dealer — the closest one is about 40 miles away — or a John Deere rep has to come visit him. Alford had an issue about a year ago; the tractor belts were loose. He waited a day for the John Deere rep.

"The tech came out and it took him a couple hours to diagnose that there was one small sensor out. And that one small sensor, I think it was a $120 part."

The problem with this setup is that in farming timing is everything. When the soil is soft enough to till you have to go; when the crop is ripe you have to pick it.

"So if you have a small problem that does not allow your tractor to operate and you have downtime it's costing you money and a lot of stress," he says.

You may wonder why Alford doesn't just break that digital lock and get into the software and fix the problems himself. He could, but he'd be breaking the law. It's called the Digital Millennium Copyright Act of 1998, or DMCA. It was written because movie studios were worried that people would break the digital locks on DVDs, make copies and pirate them.

"And now we have this situation where there's digital locks on all kinds of things," says Kyle Wiens, co-founder of iFixit, which helps people repair their own technology. "There's digital locks on your garage door opener and if you want to circumvent that, if you want to use an aftermarket garage door opener that wasn't made by your garage door manufacturer, you might be violating copyright law."