Do-it-yourself GPS Fixes

February 8, 2011 05:36 AM
Do-it-yourself GPS Fixes

Your automated steering system starts to veer off path. The swath control system on your planter stops recording passes through the field. The yield monitor on your combine suddenly is nothing more than a blank video screen.

When computerized systems go down, it can be unsettling. It’s easy to diagnose a smoking drive belt or a hydraulic hose that’s spewing oil, but the intricacies of diagnosing problems in high-tech computerized systems leave many farmers in a cold sweat.

Experts familiar with GPS, auto-steer and swath control systems say many problems related to those systems are easily diagnosed with common sense or a few basic tricks common to most computerized systems.

All computerized control systems on modern farm equipment have extensive built-in self-diagnostic capabilities. In many cases, a warning or fault code appears on the display screen when a system malfunctions.

"Warning codes alert the operator that something is wrong, but it’s not something that’s critical or bad enough to require stopping," says Erik Ehn, product manager, Trimble Agriculture Division. "Fault codes indicate something is not operating correctly and may require stopping the machine."

Check the owner’s manual or on-screen diagnostics page to identify the warning or fault code’s origin.

"Most systems record all the codes as they occur, and operators can look at them on the diagnostics page," says Brian Davis, Ag Management Solutions consultant for Schilling Brothers Inc., a John Deere dealer in Mattoon, Ill.

"The codes will tell them [the source of] the problem. Maybe they lost their GPS signal, or the steering sensor isn’t sending a signal. Or it could be something really simple like the steering wheel got bumped and that caused the auto-steer to disengage. The diagnostics page tells you where the system thinks it has a problem," he adds.

All sensors and components in auto-steer, swath control and yield monitoring systems constantly
report their status to the diagnostics page. Most diagnostics pages not only display current conditions of various components (voltage, ohms, on/off) but also list acceptable operating ranges so operators can quickly determine if components are operating within design parameters.

Puzzling, intermittent problems can sometimes be solved by monitoring the diagnostics page as the machine moves across the field to identify momentary voltage drops, blips or brief failures.
Beyond using the self-diagnostics functions to pinpoint problems, here is a list of simple problems and fixes related to GPS, auto-steer and swath control and yield monitor systems:

"S-ing" or "weaving:" Weaving on either side of the designated auto-steer line is often related to programming that affects sensitivity and reaction to computerized auto-steer inputs. But it can also be a simple mechanical problem.

"Worn mechanical steering components can cause weaving," Ehn says. "Tie-rod ends or linkages get loose and cause the auto-steer system to constantly overcorrect to compensate."
To check for worn linkages, turn the steering wheel with the machine sitting still and note if the steering tires react quickly. Replace worn ball joints or steering components. On articulated four-wheel-drive tractors, be aware that worn, loose frame pivots can contribute "slop" to steering movements and make auto-steer inaccurate.

Hydraulic leaks: If hydraulic steering cylinders or auto-steer hydraulic control valves have oil leaks, the auto-steer system may overcompensate and cause steering inaccuracy. Any oil leak on any component related to auto-steer can contribute to steering inaccuracy.

Low voltage: Display screens that go blank or display strange "hieroglyphics" hint at low system voltage. If possible, check system voltage on the diagnostics page. If the screen is inoperable, probe for voltage on the main (red) power wire in the back of the display, always using the system ground wire (black) to complete the circuit.

"The system should have at least 12 volts but not more than 14 volts from the power supply," Ehn says. "If you see less than 12, be suspicious of corrosion at the battery terminals or damage to the main power wire."

If a low-voltage problem is intermittent, consider whether other electrical components on the machine are temporarily overloading the electrical system. Auxiliary lights or extra electric controls for spray valves or row shutoffs can overtax alternators and starve voltage-sensitive components.

Wiring damage:
If computerized systems behave badly the first day after coming out of off-season storage, be suspicious of gnawed wires.

"If you don’t have any power to the system, or you’ve got sensors that don’t show up on the diagnostics page, I’d trace the wires and look for rodent damage," Ehn says, "especially on harvest equipment where crop debris attracts mice and rats."

Altering wheel spacing can cause major—or subtle—damage to electrical harnesses and connectors.

"When you move wheels out, it can stretch wiring harnesses so wires either get torn apart or stretched just enough that the wires inside the rubber insulation break but the insulation stretches and you can’t see the broken wire," Ehn says. "Another problem is that stretching the harnesses pulls apart or stretches the electrical connectors so the pins don’t make contact. Unplug the connectors and make sure all the pins and sockets are firmly seated to the same depth in all the connectors."

External interference: Business-band radios, walkie-talkies and high-intensity discharge (HID) or xenon auxiliary lights—anything that creates an electrical or magnetic field—can disrupt radio signals from orbiting satellites that guide GPS-based systems.

"I’ve seen problems with business-band radios that, when they keyed the mike, it caused them to lose their GPS signal and kicked off their auto-steer," says Davis of Schilling Brothers. "Hand-held walkie-talkie radios can do the same thing."

Keep accessory lights and antennas for business-band radios as far from GPS receivers as possible. Davis says some customers install in-line filters, purchased from their radio supplier, in their business-band radio coaxial cables to cure interference problems.

Kill to cure:
Just as many home computer problems are cured with the treasured Ctrl+Alt+Delete rebooting procedure, killing power to display consoles and processors often fixes screen freezes in ag equipment.

"If a [display] screen freezes or won’t respond to commands, the quick, easy fix is often to turn the ignition switch off, wait a minute until all the lights on the console go off and then turn the key back on," Davis says. "Rebooting fixes a lot of problems."

A "deeper" style of rebooting—the "cold boot"—is sometimes necessary because computerized systems have a constant-power circuit that bypasses the ignition switch to power the computer’s onboard memory systems when the ignition switch is off.

"To do a cold boot, unplug the wiring connector for the display screen with the key switch off," Davis says. "That removes all battery power and forces a different kind of boot-up."

Reboots and cold boots may not cure problems with GPS, auto-steer, swath control and yield monitors based in controllers (computers) external to the actual display console in the cab.

The ultimate cold boot—an extreme measure that may result in loss of programmed data—is to disconnect the machine’s batteries for a minute or two. This forces all systems to reboot and might correct problems related to freezes, lock-ups and erratic behavior.

Removing power to all electrical systems may erase programmed data, such as farm and field names, seed varieties, auto-steer tracks and even the basic physical measurements of the machine necessary for auto-steer, swath control and other GPS calculations.

That’s why it’s always a good idea to occasionally stop on an end row while the machine is operating properly and back up data to a data card or write basic programming information in a notebook for future reference.

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