Troubleshooting techniques (part 2)

by admin on December 14, 2017


From the generalist to the specialist

(Remember from part one that my mechanic had figured out nothing that I hadn’t already  figured out and had sent me to a automotive electric specialist. ) On one hand I was elated that I was as smart as the guys in the shop on the other hand I was bummed that I still didn’t know what was wrong, the car wasn’t working right and I’d spent 4 hours in the shop with my car.  On getting to the automotive electric shop I strolled in and asked for Dan.  The guy said “That’s OK, describe your problem and we’ll see if we need to get him involved.”  I relented and described the problem it in gory detail.  He turned to one of the other guys, Tim I think, and rattled off some commands about checking the voltage regulator and the ground.  I assured him the voltage regulator appeared to be functioning properly.  He smiled and motioned me towards Tim.  Tim was under the hood for all of about 90 seconds before coming out. 

Going over to the shelves, he came back with a shiny piece of copper braid about as long as a dollar bill.  He attached it from the back of the engine block to the firewall right next to the voltage regulator.  Turning the engine back on, he checked some readings and said I was good to go.  Total time less than 10 minutes cost was less than $10 including parts.  They never explained what was wrong; as they often say in high school and college “the proof is left to the student.”  They sent me on my way with the car working as it should.

What did I do?  Took it home and had to figure it out.  I checked the operation of the voltage regulator and it was the same.  So I unhooked the copper strap and could see the voltage regulator go to the limit and within a few seconds could see bubbles in some of the battery cells.  I reconnected the copper braid and the voltage regulator output reduced and the bubbles ceased within a minute or so.  I turned off the engine and said to myself: WHY? I looked and looked and finally I realized what was happening.  The alternator negative lead was connected  to the engine block.  The engine was mounted by hard rubber mounts to minimize the vibration and noise into the car.  The voltage regulator was mounted and grounded to the chassis of the car.  The strap is what made sure that the two (chassis and engine block) were at the same potential.  Without the strap, the voltage regulator couldn’t “see” the voltage so it commanded max output.

When I checked the operation of the voltage regulator and simulated the inputs, I connected the multimeter to the chassis, just like the voltage regulator.  So of course it worked properly.  The very important detail I overlooked was the ground.  Without the strap connecting the engine block to the chassis, the two were at different potentials and neither one “knew” what the other was doing.

What’s the point?  I later found out that the guy I spoke to was, in fact, Dan.  He had been doing this for so long, he was able to diagnose the most likely ailments very quickly.  He had “practiced perfectly” for decades.  I had done the right troubleshooting, but was unable to draw the right conclusions, and didn’t quite go far enough.  None of the books specifically mentioned verifying that the voltage regulator and alternator had the same ground references.

Does Practice really make Perfect?

Which takes us back to our saying: “Practice makes perfect.”   This really isn’t completely true as my driver education teacher taught me more than 30 years ago.  The expression that he preferred and used was: “Perfect practice makes perfect.” His explanation was simple “If you practice making a mistake in the car with me sitting next to you, you’ll do the same when I’m not sitting here.”  I can, to this day, remember the grin on his face as I tried to pull away from a stop sign and the engine merely revved and we went nowhere.  It seems I had tried to do a “California stop” even though I was in beautiful eastern Pennsylvania.  For the uninitiated, a California Stop is where you slow the car way down, but never completely stop.  Remember the sign does say “STOP” it doesn’t say “stop only if”, or “roll”.  It says stop.  When my oldest child approached driving age, I reassessed my driving habits and made some adjustments.  I realize that they learn a lot from example, so I wanted to be sure to be doing the right things.  Here I am again, four years later with number two teenager.  Time to re-evaluate my driving, again.

What does any of this have to do with running an electronics repair shop?

Although I’ve never owned an electronics repair shop, I have fixed televisons, computers and all sorts of electrical and electronic equipment.  I’ve worked on some very complex military electronics systems including an inertial navigators, radar, time standard, radios etc.  [to be continued...]

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