Tools

What You'll Build

A diagnostic bench for a machine the dealer can't figure out.

A laptop listens to the machine's computers. A scope watches the wires.

The agent reads both at once and flags where they disagree.

Then you swap parts and compare against a machine that runs fine. Until the difference goes away.

The Story

A farmer's John Deere combine had electrical trouble for several days.

They paid a Deere mechanic to come out. They'd done that about twice in ten years. He couldn't find it.

I worked with Hermes running Astra, we build a test suite for CanBUS that used a PCan USB adapter to read CanBUS messages and a Rigol 4-channel oscilloscope that I barely know how to run but has a network adapter on it.

The test suite ran while they talked to the agent on a laptop.

it seemed to be able to figure out the CanBUS messages and would also compare the electronic traces it pulled from the scope against what it was seeing for messages.

They worked it the way a good mechanic would. Talk through the procedure. Pull a controller. Test again.

The key move was the second combine.

We would discuss the diagnostic procedure and pull controllers and compare results against traces that I'd pulled from another working combine I have.

Two bad controllers turned up. Each tool caught one.

one that was pulling the CanH line low randomly (the Rigol caught that) and one that would hold the bus hostage and messages would drop off a cliff (the Pcan found that).

In plain terms: one part was randomly shorting a signal wire. The other was hogging the line so nothing else could talk.

Their scoreboard:

JD:0 Hermes:1

The Manuals Were the Other Half

In the comments, the farmer pushed back on the easy story.

They said the "you can't fix your tractor" line doesn't match their experience. They fix pretty much everything themselves. The few times they've called the local Deere mechanics, it either didn't get fixed or they were just too busy to do it themselves.

What they do need help with is the paperwork.

pretty much anything else I've been able to do via the 10k page diagnostic and repair manuals they sell you for $50. Now I do actually need AI for those because they're ridiculously complex to use.

I fed them into a RAG system Hermes build and I just ask questions now. It's 10X more useful that way.

A RAG system is a searchable library the AI reads from before it answers. So the answer comes straight out of the manual.

That part needs no scope and no adapter. Just the manuals you already bought.

The Business Angle

The service call is the expensive part of a breakdown. The downtime is worse.

A mechanic who drives out and leaves without an answer costs you both.

This owner already had the skills. The agent gave them two things they didn't have. A reader for 10,000 pages of manual. And a partner that could watch two instruments at once and say what changed.

It doesn't stop at the repair.

They're now pulling data off the combine to build their own yield monitor. Yield from the CAN bus, position from their RTK GPS module and base station.

something I've wanted for years but didn't want to pay $20k to put in.

The combines are 20 years old. They can already read engine speed, coolant and ground speed. Next is a camera on the cab displays, so the video lines up with the machine data.

Who Should Steal This Idea

Farmers running older equipment they already maintain themselves.

Fleet and construction owners with a yard full of machines and a dealer who is always booked.

Repair shops that own the service manuals and lose hours paging through them.

Anyone with two of the same machine, where one works. That second machine is your answer key.

How Hard Is It

Hard. Be honest with yourself here.

This owner fixes their own equipment and already knew what a controller was and where to pull one. The agent made them faster. The skill was already theirs.

The manuals part is different. Loading the repair manuals into an agent you can question is the step most owners can do. Start there.

Cost: not stated. The manuals were $50. The adapter and scope prices were not given. Someone in the thread asked what the service call and the AI usage cost. No answer was posted.

Gotchas and Tips

Get a working reference first. The whole diagnosis rested on comparing against a good combine. Without one, you're guessing at what normal looks like.

Two tools caught two faults. The scope found the wire problem. The bus reader found the traffic problem. Either one alone would have missed half.

Older machines are easier. A commenter noted that on Deere equipment you can read the industry-standard messages, but past that "JD has it locked down pretty good." The owner's take: these combines are 20 years old, and they doubt Deere was doing much more than obfuscation back then. Newer machines may not open up like this.

You still make the call. The agent read the signals and suggested what to test. The farmer pulled the parts and decided.

Don't reflash anything on a guess. The owner said they haven't tried replacing the software on an engine controller. Know where your own line is.

Got a machine that's been down for days and a manual nobody can read? Which one do you start with?

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