The Rational Art of Troubleshooting

This email from one of my Live Help disciples is a great illustration of the kind of attention to detail and concentration you need to have while troubleshooting. I like to call troubleshooting the “rational art.” Yes, there are techniques and cause-and-effect relationships that you need to know but, as illustrated in this repair story, there’s also something more, something supra-rational that isn’t learned in text books; this is the Edge of the troubleshooting katana.

In this repair story, my apprentice, Chris, is struggling with a GE wall oven that kept throwing an F3 code while in use. Typical of most F-codes, the manual simply says to check the sensor and its connector. Chris did this and found nothing unusual. The sensor resistance at room temp was normal. We talked about it on the phone and I recommended that he get another sensor resistance reading at a higher temp to rule out the possibility of a non-linear response from the sensor. This is where the story picks up.

Samurai Appliance Repair Man

Sent from my iPhone

Begin forwarded message:

From: Chris H.
Date: September 13, 2007 6:18:20 PM EDT
To: Samurai Appliance Repair Man
Subject: success!


FYI I did test the oven sensor. It was perfect at boiling water. So I set it in a pan of cooking oil and used my turkey fryer thermometer, cranked the oil up to 500 degrees with the sensor in it, hooked to my multimeter.

Its supposed to do ~2 ohms for every degree F above room temp. So at 212 in water it drew almost exactly 1380 OHMS, could even watch it go up with the heat. Same with the oil at 400 degress it was supposed to draw 1756 ohms and at first it was perfect at about 1790 OHMS. I was bummed at first and gave up but after a few more minutes, actually as I turned it off it jumped to 2400 ohms around 440 degrees! This is incorrect, it should be 1836ohms at 440. As it cooled, the ohms stayed in the 2400 range until around 300, then jumped back down to 1550 or so. Interesting. Not sure what went wrong in the sensor to be so erratic. Its 11 years old and get heavy use.

A new sensor has been placed and all is functioning well. The new one did come with ceramic wire nuts BTW.

another samurai success story.



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