Probing Auto Electronics

Help your neighbor identify his car s problem and be an electronics hero!

Hugh Wells W6WTU 1411 18th Street Manhattan Beach CA 90266-4025

Being a ham, you're expected to know everything about electronics regardless of the application. So have you ever had some neighbors drop over and indicate thai they needed your help with their car? Chances are, they've indicated thai it won't start or runs poorly, or that the battery is dead.

in most eases, the symptoms described seldom lit the actual situation. Bui because you're a hum, you re looked upon to he "the neighborhood electronics resource/ So how do \ou approach the problem?

L)o >oli agree to lake a look? Or do sou shine them on and suggest that they go see the local mechanic? I el s assume that voir re at least willing to take it look at the problem to help sort out the details, which may lead to a solution if the problem is electrical. And if iTs mechanical, sou may have to suggest the mechanic after all.

Electrical problems and solutions in older ears were usually easy to sort out. but the computers used in modern cars make the problems more difficult for a ham to diagnose. In fact, the

•v things that one might he able to do are limited to only a few things, but those

10 73 Amateur Radto Today * December 19

could ha\e an identifiable solution w ithin your grasp.

Three situations are discussed here that can help solve man) aggravating problems that cars experience and are not under computer control These situations involve the spark plugs and HV wiring, alternator and battery, and current leakage paths that run a battery down unexpectedly. The test (equipment for troubleshooting these three situations is typically available on a ham's workbench; oscilloscope: digital voltmeter/ ammeter; and #1157 (or #1034> tail fight bulb. So there is \crv little financial in-\estmeni required, beyond what a ham normally has available.

Most hams have had some exposure to Ohm's law problems as part of their electronics training. The logic and circuitry involved in Ohm's law problems is exactly the same as thai required for solving electrical problems in a car s electrical system. Troubleshooting then becomes a matter of developing a plan or procedure to follow in sorting out the various measurements and symptoms.

Spark plugs

Being able to diagnose a problem in an automobile's high voltage ignition system is hoih interesting and satisfying. Because of the pulse nature of the system, it can he analyzed dynamically. I sing an oscilloscope provides a means of" looking at the HV pulses for one or all of the cylinders. Observed m-

conditions can be related to inequality of spark, weak spark, shorted spark plug, defective plug wiring, or intermittent plug firing.

In the case of a standard ignition system (points and capacitor), the point's dwell time can also be observed to determine if coil saturation is being achieved. Dwell time is not a factor in electronic ignition systems. The oscilloscope display can be focused for detailed analysis on one or all of the spark plugs lo help sort out differences between themT

To make up an engine analyzer using an oscilloseopc. it will be necessary to make up a couple of interface boards lo be used as scope probes as shown in Figs. I and 2. Sync for the horizontal of the scope obtained from the high voltage using ihe circuit shown in Fig-1. A wire cuff or broadfaced spring clip is used to provide a capacitive coupling to the HV wire, as a direct connection is not desirable. The circuit integrates the HV pulse to create a single coil-


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