As of this year, California requires Enhanced Area Smog Test and Repair stations to have a digital storage oscilloscope (DSO) or graphing multimeter (in addition to a BAR 97 EIS) to continue to operate in the new program. Other states may follow suit. Ready or not, the lab scope is becoming a mainstream tool.

The third wave
Automotive technicians have been using DSOs since the early 1990s when the Fluke 97 and Tektronix 222a were introduced. A few technicians using CompuServe began posting waveforms online during 1992. At that time, lab scope usage was extremely rare. Around 1994-1995, a second wave arrived. Many more of us began using lab scopes. We were inspired from what we learned from the first-generation scope gurus online. The onset of the Internet and the World Wide Web explosion have been a boon for techs desiring to stay on the cutting edge. Using the Web's powerful communication features has enabled technicians the world over to learn and share much technical knowledge, including lab scope techniques and expertise. Finally, 1997-1998 marks the coming of the third wave lab scope user. Many more shops are moving into DSO use for the first time and they need a primer on how to get started and where to go for more information.

Why a lab scope?
Why have a lab scope anyway? A lab scope enables you to look inside electrical circuits and components. A DSO can give you a picture of an engine performance event that you can hold in the palm of your hand. These pictures are called waveforms. A waveform is a picture of voltage over time drawn across the screen of the DSO. The voltage scale is read from bottom to the top. Time is measured from left to right. It displays the electrical activity within the wire or component that you are testing. Figure 1 demonstrates how a waveform can show you how a circuit works.

It's visual
We technicians are visual thinkers. The old-timers and maybe even the younger techs remember how you ended up in this trade. It wasn't because you were good at math and other "pencil pushing" tasks. You rather gravitated toward this field because you were good with your hands and had a lot of physical energy. You enjoyed taking things apart and putting them back together. We get satisfaction in being able to see it, understand it and then fix it. Without a scope, electricity is not something you can see, therefore it is often misunderstood. Many mechanics just change parts when electrical problems come in. They don't understand how the systems work and don't take the time to read the manuals to learn how.

Mechanics are very skilled with their hands, but many of them are not readers. Technicians employ good reading and comprehension skills to get an overview of how the systems work, perusing technical information systems and studying wiring diagrams. However, even with a CD-ROM system, sometimes there just isn't enough information to explain how a particular system or component works. Even a good technician can get overwhelmed. Maybe he does not completely understand the wiring diagram, or maybe the diagram has errors in it or the wrong color codes.

The technician with a DSO at his disposal has the edge in solving tough diagnostic dilemmas because his scope and a wiring diagram will show him how the system works. Figure 3 gives valuable insight that is helpful in tracking down GM's infamous code 42.

The joy of learning
Before a lab scope and waveforms can become profitable to you, the basics must be learned. Ah, the basics. Isn't that the part that we want to just skip over so we can get to the good part? As Ralph Birnbaum said, "The basics are the good part!" When we master the basics, we can conquer the advanced stuff. Without having the basics down, all the trick advanced techniques will go right over your head - in fact, you'll be scratching it!

One must go through a learning cycle before the tool will help. Fortunately, the learning experience is a fascinating one. It reminds me of seventh grade science class. The wonder of viewing previously unseen objects under a microscope was like exploring a new world. Scoping a circuit to learn how it works is enjoyable, sort of like using a microscope. The lab scope is your viewfinder to the world of electronics. Understand electricity and you will understand any automotive control system that the engineers can design.

Learning to use a lab scope is less intimidating if you remember that it's actually just a visual high-tech voltmeter. Voltage is electricity, and electricity does not change - it follows natural laws.

Electronics will come alive to you when you finally see what's going on inside of common, everyday circuits.

Where to begin
To become skillful, you must be willing and able to learn new things. Do you love to learn? If so, the process will be exciting and never-ending. First, you must understand how to operate your instrument. That can be done by studying the manual that came with the scope. The operator's manual will acquaint you with which buttons to push. The automatic setups in today's scopes are just a starting point. You need to learn how to manually set up a scope to acquire useful waveforms on a consistent basis.

There is terminology that you need to become familiar with. Space does not permit a full glossary here. See the sidebar for where you can obtain a good scope terms glossary. Trigger, slope, timebase and coupling are terms used to describe how to set up the scope to capture waveforms. Terms like amplitude, frequency and signature describe waveform characteristics.

The big three
There are three basic waveform types or categories. Once you master these three, you will be on your way to deciphering any waveform. The waveform in Figure 1 is comprised of two of three types listed below. In fact, with practice, you will be able to look at a wiring diagram and see in your mind's eye what the waveform should look like. The three basic waveform types are: alternating current (AC); direct current (DC); and pulse trains.

AC signals generally alternate above and below the zero line. Examples include magnetic crank sensors, ABS wheel speed sensors and cam sensors. Figure 2 is an AC waveform.

DC signals are analog voltage signals. Examples are vane airflow meters, throttle position sensors and just plain battery voltage. Figure 4 is a DC signal.

Pulse trains are digital signals. They are always generated by a device that contains a transistor or Hall-effect switch. Digital signals are always on or off. Pulse trains come in three flavors: frequency modulated, pulse width modulated or serial data multiplexed.

Serial data is a pattern similar to Morse code. To interpret serial data, you need a scan tool or a computer that is programmed to read the data stream. However, looking at a serial data waveform can help you clinch a suspect power control module (PCM) diagnosis.

Figure 3 shows two pulse trains.

A foundation in electronics is very helpful in learning waveforms. To learn more about electronics, take a class or two at a local community college, or just read all you can. See the sidebar on page 14 for learning resources. You can learn more about lab scopes and waveforms with a home study course. With it you can work at your own pace. Excellent home study courses on DSOs are available from NAPA, Fluke and at least one software program, called Wavefile AutoPro.

After learning some basics, you'll be ready to use waveforms to actually fix cars. If you begin using waveforms before you have the basics out of the way, you won't get very far. You'll have more questions than answers. Nevertheless, a few waveforms are presented here to get you started.

A different approach to diagnosis
The examples given here are merely the tip of the iceberg. The waveforms that a DSO can capture, display, print and save give you a whole new approach to solving diagnostic dilemmas. You don't have to be constrained by the manual, or lack of one. No longer are you tethered like a ball and chain to semi-worthless flow charts.

Select the method you would rather use to diagnose a car: one, follow steps you don't fully understand as you follow a flow chart with your scan tool and DVOM like a rat in a maze; or two, use the manual as a reference as you methodically gather information that leads you to a confident diagnosis. The diagnosis can be proved with a waveform before the parts are ordered.

Scope in your toolbox?
OK, if you suddenly had a DSO in your toolbox, how would you begin to use it? Maybe you've had one for a while that's gathering more dust than use. Here's how you can gain expertise.

• Study the operator's manual.
• Use a simulator board.
• Start a home study course.
• Use a personal computer to access the International Automotive Technicians' Network (iATN) on the Web.
• Use iATN to learn from first and second wave lab scope gurus.

If you're serious, buy a PC lab scope program to save, analyze and catalog waveforms. It's a great way to learn waveforms and document your work. You will also be able to share waveforms with others and talk over case histories.

How to use a lab scope
Pin-point testing: When your scanner indicates a problem with a particular circuit, your DSO can quickly probe that circuit and its components, good or bad.

Quick checks: Take less than five minutes to perform quick checks. Figure 3 is a closed loop and O2 sensor quick check. As your skills increase, you will learn other quick checks for fuel pumps, ignition modules and coils.

A lab scope does not become obsolete. Will your DVOM ever become obsolete? Heavens no! Each tool has its purpose, strengths and weaknesses. A DSO works by the commands of a knowledgeable owner. The processor that drives this tool is more powerful than the fastest computer - it's your brain. If you use your brain to learn the use this tool, you will be equipped for challenges of today and tomorrow.

Henry Guzman is an ASE master tech with L1 certification. He has 20 years of professional experience.

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