Real Quality Design

When I worked in medical devices, I was regularly struck by the fact that my previous employer, QSC Audio Products, was more concerned with reliability and quality control than either of the two pacemaker/ICD manufacturers" for whom I worked for 10 years after I’d left QSC. I wasn’t shy about expressing that opinion to the people in charge of caring about those two qualities, either. I made that statement to VP’s of Regulatory and Legal and R&D and reliability assurance. I said those words to middle managers, engineers, other reliability engineers and managers, and on occasion to doctors. You’d think that would have terrified, irritated, embarrassed, or pissed-off someone in the grossly over-priced, self-absorbed, and mindlessly corrupt medical industry; but you’d be wrong and disappointed. I don’t think anyone to whom I made that claim even bothered to take it seriously enough to consider the insult and outrage I intended. Usually, the statement just got a laugh. It was, however, a fact and an outrage.

This past evening I repaired an electric bass amp that’s been lying around in my shop for several years. The positive impression I had of the amp’s manufacturer from the availability of service information on their products vanished when I opened the case and saw the probable cause of the amp’s failure before I’d applied a single piece of troubleshooting test equipment: lots of failed solder connections and terrible mechanical design that put almost ever electronic component in either incredible mechanical stress or at the far end of a diving board that would toss the components until they broke or flew off of the circuit board. When I did use some test equipment I discovered the amp’s output and driver transistors were fried on the negative side of the AB₁ output and the bias and driver transistors were fried on the positive side. Probably all of that damage was likely caused by the heatsink vibrating all of the output transistor leads free from the circuit board.

At QSC, we used an assortment of moderately sophisticated and primitive vibration, shock, and thermal tests that sometimes demonstrated what was mechanically weak in a design in a few minutes. There were very few components that didn’t receive a stress-relief bend (or two). Components with substantial mass received two different securing methods (screws and glue, glue and silicone rubber, or strap and glue). We tested-in over-voltage and power safety margins; sometimes with batch testing and sometimes with individual transistor tests. We had controls that tracked component lots so, if problems arose in production or in use, we knew where those components ended up: product and location. When our customers sent in their postage-paid warranty registration information, we even knew which customers had the products with the problem components. There was a lot of thought, expense, and care that went into making our power amplifiers (all we made back then) the toughest the industry had ever seen. (This really sounds like a commercial, doesn’t it? It isn’t, since I don’t know anything about QSC products produced since about 1993. The last generation of QSC amps I worked on was the EX stuff.)

This bass amp that I just repaired was closer to medical device equipment than QSC’s best stuff from the 1980’s . About half of the weight of the circuit board was supported by the leads of 8 power transistors. The leads were cut straight, which guaranteed that the weak link in that chain would break under vibration conditions. The weak link would always be the solder connections, especially because the circuit board pads were all too small to provide a strong connection. The design abused the strength of several other components and demonstrated a scary lack of mechanical design skills.

I fixed a few of the design’s problems in the repair, but the worst faults are simply too built-in to the design to resolve in a reasonable amount of time. So, it’s back-to-life, but for how long? Some things really aren’t worth repairing let alone improving. The experience reminded me of how lucky I was to have worked for a company that was focused on providing value to its customers and doing the job as well as possible under the constraints of economics and customer expectations. That was a rare opportunity.