CAPA Corner: The Case of the Defunct TV
Several years ago after a long Monday on the road traveling to a client, I called my lovely bride to see how her day was going. Unfortunately it was not going well as I was greeted with the news that our television was not working! Now this television was only a month old. We had gone out one beautiful spring morning to purchase it and I had spent that gorgeous afternoon inside the house installing it in the entertainment center. I could feel the anger swelling inside me as I thought about the expense and the afternoon I had devoted to setting it up.
Step 1: Define the performance problem
Then I thought, “Wait a minute, you do this every day!” I reached down into my computer bag and pulled out the trusty, laminated Investigation Roadmap. “OK,” I thought, “I need to understand the problem.”
At this point I nearly made the lethal error of asking my beloved, “What specific object has the defect?” Sanity, however, miraculously intervened and I instead proceeded to ask the what questions in a much more conversational tone.
She repeated that the TV was not working. When I inquired about describing that in more detail (the defect characteristics) I learned that when the TV was powered up, the screen remained blank and there was no sound. In my mind I starting constructing the IS / IS NOT Diagram.
| WHAT | IS | IS NOT |
| Defective object: television | Any other appliance | |
| Defect: Nothing happens when powering up the TV | Fire, explosion, smoke, etc. | |
| Characteristics: blank screen, no sound |
Distorted picture, unintelligible sound
|
| WHEN | IS | IS NOT |
|
Defect 1st seen: about 5:30 PM (half an hour ago when she had turned the TV on for the first time that day) |
The evening before (the last time the TV had been used) |
Step 2: Collect data
- Television programming from a cable box; and
- Recorded programming from the DVD player.
I decided to experiment to better understand the defect itself. I asked my bride to play a DVD on the DVD player. “Tom, it works! There is both a picture and sound!”
This was revealing. First, I now knew the TV worked. The signal from the DVD player provided both a vibrant picture and clear sound. Second, I recognized that there was nothing wrong with the DVD input. The second experiment followed as I asked her to switch to the television programming.
“Tom, it’s back to a blank screen and no sound!”
As I explained earlier I had spent a gorgeous spring afternoon inside the house installing the TV. The TV had a great picture and sound when operating in the DVD mode. I was still searching for a change, but the change was not in the TV or the DVD player. Both those devices were eliminated from the investigation. And since the TV worked fine, there was no issue with the power connection. The search area had become quite small. The investigation had quickly focused on the cable box.
“Toni, is there power to the cable box?”
“Yes, the display is lit up and shows the time.”
I now knew the change. If the power to the cable box is turned off, the display indicates the time. If the power is on, the display indicates the channel. “Toni, push the power button on the cable box.”
“Tom, we have television reception! We have both a picture and sound!”
Step 5
The technical route cause was obvious. When the TV had been turned off the night before, someone must have pushed the power button on the cable box and turned the power off. My wife and I never did that. We simply powered off the TV itself. However, one of our sons had spent the weekend with us and had been watching the TV when we had gone to bed. Bingo! He had powered off the cable box. That was the change I had been searching for.
Technical Root Cause: Son had powered off the cable box.
This was a simple investigation. I had not needed to do Step 3: Identify Possible Causes or Step 4: Test Possible Causes.
This is how he always turns off a TV.
Because we didn’t tell him to do it our way.
Why didn’t we tell him to power off the TV the way we do?
Because we didn’t think of it.
Why didn’t we think of it?
???
Systemic Root Cause (system failure): We (Mom and Dad) hadn’t thought to explain to our son how we shut down the TV.
Second, was there a detection failure? Why hadn’t we discovered that the TV did not work? Actually, we did discover the problem the next time the TV was powered up!
Systemic Root Cause (detection failure): There was none. We had discovered the problem at the earliest opportunity.
Step 6: Determine Corrective / Preventive Action
Step 7: Verify Corrective / Preventive Action
| Type of Root Cause | Root Cause | Corrective Action | Risk Mitigation | Control Plan | Acceptance Criteria | Actual Measures |
| Technical | Son had powered off the cable box |
Pushed the power button on the cable box |
Insignificant. Accept Risk. |
If problem recurs, power up the cable box. |
TV receives both picture and sound |
TV did receive both picture and sound |
| Systemic | We hadn’t explained how to power off the TV |
In the future we would need to explain to guests how to power off the TV. |
Insignificant. Accept Risk. |
If problem recurs, power up the cable box. |
Problem does not recur |
Problem has not recurred several years later |
Conclusion
As I said at the beginning, a root cause investigation may be formal or informal. Things happen at work, at home, anywhere. The investigation methodology remains the same. Only the level of documentation changes to fit the situation. In this very informal situation there was no tangible documentation. I simply made mental notes in my head. However, the investigation methodology had once again been reinforced, building confidence and honing my skill sets.
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