I used a Concentration Diagram to solve my first problem for Red X certification. The die casting department had a big reject problem due to porosity. The castings had to be 100% visually inspected or else assemblies downstream would fail leak test and result in more expensive scrap. As I recall, this problem was costing them $75K/month. The engineers had spent weeks studying scrap parts, trying different settings, all in an attempt to minimize porosity voids. The voids which intersect the center bore were the biggest concern.
The Quality Engineer from the die cast department and I went through the scrap pile with a piece of graph paper, and in 10 minutes, we had prepared Diagram A on the left (I no longer have the original, so this is a re-creation). I remember our conversation, "It looks pretty random to me." Then, in a flash of genius, I suggested we turn the picture 90°. He measured the depth of the porosity voids with a ruler and a flashlight, and in 10 minutes I had prepared Diagram B. My friend looked at the picture and said "Oh my gosh, do you know what that means?" I said I could see it was not random, but I didn't know what it meant. He said the problem was the bung. I said I don't know what a bung is. He said the bung is the slug which forms where the two halves of the die cast mold come together. All the porosity was at the dividing line between the mold halves. The solution was to re-make the mold cavity and move the bung an inch higher. That way, any porosity which formed was in a non-critical area.
The morale of the story, the concentration diagram alone was not enough to see the answer, the quality engineer's knowledge of casting was not enough to solve the problem, but put those two together and we solved a $75K problem in 20 minutes. Turning a random problem on its side for a new perspective was also key to this success. I often say, "random" is more a statement of our ignorance than any useful description of the problem. I also say, if your quality people can solve a $75K problem in 20 minutes with proper tools, why would you have them do anything else?