Power at Work: Have you read your shop manual lately?

Wednesday, November 4, 2009

With this in your hand, you should be able to do repairs yourself or at least narrow down the potential fault locations for a service rep

by RALPH WINFIELD

Most of us are inundated with operator's manuals for everything from the bench grinder to the combine. In many cases, these manuals tell us how to start and stop the equipment, when to service it and the importance of operating the equipment safely. That is all good and useful information, but why should it stop there?

In the days when tractors were much simpler, the electrical wiring and hydraulic systems were much simpler as well. For example, in earlier years, each electrical circuit or wire on a tractor could literally be viewed from end to end in a matter of seconds. If that tractor didn't start because of an electrical problem, the possible causes could be analyzed quickly with a voltage probe or jumper wire by anyone with a basic knowledge of electrical circuitry.

Fortunately or unfortunately, technology has progressed in the last 40 years. We have demanded tractors and combines with cabs, air conditioning, and many toggle (temporary contact) switch controls. These functions certainly make for greater operator comfort, convenience and efficiency.

But these more sophisticated machines do tend to age and many of us cannot afford to upgrade to new units every two or three years. Thus, aging starts to take its toll on electrical devices and connectors (connections) as fatigue and corrosion become more aggressive. What commonly happens is that we begin to see transient electrical faults occurring. By transient, I mean those "come and go" faults that are often the most difficult to locate and correct.

That's where a good shop manual becomes invaluable. The schematic of a typical engine start relay, for example, shows the four wiring connector points. Two of them will be shown as the pull-in coil, which for example would be energized by the key in the start position to close the relay so power is supplied to the starter motor. That would be a normally open (NO) relay.

However, other devices would also appear in that start relay circuit. One would be a neutral start switch (or clutch down switch) that would keep the circuit open if that switch is not closed by one of the gear shift levers being in the neutral position or the clutch being in the fully down position.

By contrast, the electrical relay or solenoid switch on or next to most newer diesel injection pumps (those that do not have the old mechanical shut off) are of the normally closed (NC) type. When the key is in the start or run position, the solenoid (relay) coil will be energized so diesel fuel can flow to the injection pump.

A list of symbols and descriptions should always accompany an electrical schematic drawing to assist in locating the device.

If a device (relay, solenoid or switch) is not faulty, then the continuity problem in the electrical circuit is often a corroded or loose connection.

Replacing most complete wiring harnesses to correct a corroded pin in a multi-pin connector is a very expensive solution that can and, I am sure, does occur.

Individual pin connectors in multi-pin connectors can be replaced if, and only if, the corroded pin can be identified. In most cases, this will require the removal and installation of both parts of a connector, one in each side of a multi-pin connector.

By using a good set of electrical schematics, a complete current path can be identified. When it is established, often a jumper wire can be a much faster and cheaper solution. Please note the words "complete current path." It is absolutely essential that safety switches and fuses (breakers) not be bypassed with those jumper wires.
Some points to remember:

•     When replacing connector pins or putting ends on jumper wires, do get out your soldering unit and make good connections that are not as likely to corrode as the straight crimped fitting.
•     Good grounds are absolutely essential to ensure full voltage to all components, but especially with the newer electronic components, such as dashes or GPS units. A high-resistance ground connection can be a significant cause of transient or complete system malfunction.
•     Please make sure all ground connections are clean and then coated with dielectric compound, which should be in every farm shop. Also use it on both battery terminals of every battery you own.

Most larger farm operations should have at least one team member who looks after the machinery. That person is likely to have a good voltmeter (multimeter) and a good understanding of electrical circuitry.

Now, if we can just get a good set of electrical schematics for each tractor and combine in that team member's hands, he or she would be able to do most electrical system troubleshooting and repair or be able to at least narrow down the potential fault locations for a dealership service person. BF

Agricultural engineer Ralph Winfield farms at Belmont in Elgin County.