The DIY Auto Mechanic and the Digital Storage Oscilloscope (DSO)

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The days when the serious diy mechanic, then known affectionately as a “shade tree mechanic,” could get away with a few simple test instrument like a tach/dwell meter, a vacuum gage, compression tester, timing light, exhaust gas analyzer, Multimeter, etc. are gone forever. Today’s cars with all their onboard computers require many specialized test instruments with Scan tools, digital Multimeter and digital storage oscilloscopes right at the top of the list. In this factoid I will introduce you to the DSO, also known as a Dual-Trace Oscilloscope. Next to a scan tool a DSO is one of the most important tools a mechanic can own and you should be thinking about purchasing one. Add one to your online wish lists and maybe someone will surprise you with one for your birthday or some other special occasion.

First of all let me explain that a scope is not a substitute for a scan tool, digital Multimeter, breakout box, engine analyzer, exhaust analyzer or any other test instrument but works in conjunction with those instruments to speed up the troubleshooting procedure and helps isolate the cause of the problem to a specific component. The DSO allows you to see visually what is really going on inside all the onboard electronics. Many DSOs also allow you to print out a permanent record of your observations much like an EKG machine prints out a hard copy of your heart beat pattern for the cardiologist.

Scan tools display all kind of fault codes, voltage readings and other numbers but these numbers alone don’t give you a complete picture of what’s going on with the onboard computers and sensors. Some problems don’t even produce a fault code yet effect the performance of your vehicle. Intermittent problems are the worse kind of problem any mechanic can face because they have a habit of coming and going so fast that normal test instruments are no help at all and that where the DSO really shines because no matter how fast an intermittent happens the DSO will capture and store all the critical reading at that instant in time for you to study and analyze even after the intermittent condition has past. Let’s say your car hesitates on acceleration and you suspect the TPS (Throttle Position Sensor) to be the cause of the problem. The numerical reading given by your scan tool tells you that the TPI is functioning properly, but is it really functioning properly? Hesitation usually occurs between idle and part throttle and is caused by a dead spot on TPI that is too small to show up with a scan tool but will show up on the visual wave form produced by the DSO.

Learning how to set up and use a DSO, learning how to interpret the wave forms it displays isn’t something you are going to master in a few hours or over night, it will take time and practice. Fortunately most DSOs come with very detailed operating manuals. DSOs are also very expensive and can cost thousands of dollar but an excellent one for the auto mechanic can be had for under $300 from Vetco Electronics online http://shop.vetcosurplus.com/catalog/product_info.php?cPath=36_41&products_id=1579.  The Velleman Personal Scope 10/ms is all the DSO that you will ever need for service cars, trucks, SUVs, ATVs, etc. You can download a PDF manual for this DSO here http://www.vellemanusa.com/downloads/0/manual_hps40_10-uk.pdf. This DSO can also be used to service other electrical and electronic equipment beside those found on motor vehicles which makes it an excellent invest ment.

Unlike a scan tool that you set up by entering your vehicles VIN, you set up a DSO by telling it how you want it to display the data i.e. the voltage scale, time base, trigger point, display orientation, etc. Most DSOs, the Velleman 10/ms included, are menu driven so making these setup adjustments are relatively easy.

The DSO, unlike any other test instrument gives you a complete snapshot view of all the electronics and shows how they are functioning one to another. You name it, TPI, ABS, O2 sensors, fuel injectors, spark timing, etc. the DSO will show you graphically exactly how these devices are functioning.

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