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posted: June 8, 2024
tl;dr: The reasons that some products just cannot be repaired, no matter what...
I am suffering through a months-long process to attempt to repair the six year-old Samsung RS25J500DSR refrigerator in the house I am renting. Seven attempts (repair visits) have been made so far, all resulting in failure. What started out as one symptom, a failure of the chiller compartment to reach a properly cool temperature range, has expanded into three more problems: a malfunctioning control panel, an ice maker that does not make ice, and a water dispenser that does not dispense water. The chiller’s temperature sensor has been replaced twice, the fan that blows cold air from the freezer compartment to the chiller has been replaced, the main motherboard/controller has been replaced, and a new control panel was installed, which worked for less than a day. Things are getting worse, not better.
This is not a surprise to me, as an engineer who worked for several companies that had manufacturing facilities that built physical products with electronics in them. I’ve been on assembly lines, designed products that were built in factories, and I’ve debugged manufacturing issues. Yet apparently it is a surprise to the repair service, the insurance company that wrote the policy covering the repair work on the refrigerator, and the owner of the refrigerator. Most people think that, in general, anything can be repaired: you just find the faulty part or subsystem, replace it with a good one, and the product will work again, right? Unfortunately it is not that simple, so I’m taking this opportunity to document why some physical products just cannot be repaired.
Lack of modularity
Some products, in this age of electronics, are little more than a box that contains one large circuit board, along with a few input and output devices, such as a screen and buttons. This is the way that most smartphones are constructed. If the screen or the buttons go bad they might be able to be replaced, but if something goes wrong on the circuit board, which is most of the cost of the device, you’ll probably have to buy a new smartphone.
Tiny parts
It used to be that the parts on electronic circuit boards were placed there by human beings on the assembly line. Nowadays this is all done by robotic pick-and-place machines, which can handle much smaller parts than can human fingers. Manufacturers have taken advantage of this to shrink all the part sizes, which shrinks the size of the final product. Yet it can make it impossible in the field for a bad part to be swapped out. Any attempt to do so may damage the circuit board or other nearby parts. So usually the entire circuit board is replaced, which may lead into the situation described just above of needing to buy a new product.
This Samsung refrigerator used to have one problem, and now after seven repair visits it has four problems
Poor tolerances
This is likely the issue that has doomed my Samsung refrigerator, and is one of the key differences between cheap products and more expensive products. Cheap products will be designed and built with components that have looser tolerances. In the factory, if the loose tolerances cause the product not to work after it is built, some other parts can be swapped in until the product functions. Yet once the product gets out into the field, it is much harder to do this, as the replacement part may not work in the overall system.
Every part is built to specifications, and those specifications have a range or tolerance associated with them. A 100 ohm resistor will not always measure exactly 100.0000 ohms. If the tolerance is +/- 1%, it will range from 99 ohms to 101 ohms and still be called a 100 ohm resistor. At +/- 5% it can range from 95 ohms to 105 ohms, and at +/- 10% it can range from 90 ohms to 110 ohms. It’s more expensive to buy parts with tighter tolerances, so cheaper products will typically have looser tolerances.
To make this easier to visualize, consider a door frame and a door. Nominally the door frame is 100cm wide and the door is 99cm wide so that it fits inside the door frame. But in actuality there will be variability in both the size of the door frame and the door. If both parts have a tolerance of +/- 1cm, often the door will fit inside the door frame but sometimes it won’t. The door frame might be on the small side, at 99cm, and the door might be on the large side, at 100cm. In the factory, when this happens, what they do is search for a door that’s also on the small side, at 98cm, to fit inside the 99cm door frame. But out in the field, if the door goes bad and needs to be replaced, the replacement door might be the nominal size of 99cm or even 100cm, and it won’t fit. You might have to go through many replacement doors before you finally find one that’s also on the small side and fits.
This is a mechanical example, which hopefully most people can understand, but the same concept applies in electronics.
Factory tuning required
One way of dealing with the tolerance issue is to add something to the circuitry that can be tuned or adjusted in the factory until the product works. This actually introduces some final variability which can be controlled. Back to the door frame example: imagine a door frame that has an edge that can be adjusted by turning a screw to make it move in or out by 1cm. If a 100cm door shows up, the screw is turned to move the edge out so that the door frame is 101cm wide, and everything works.
The same tuning concept applies in electronics circuits, but often the tuning requires specialized equipment or access to the circuitry which can only take place in the factory. The field technician may not even be told about the tuning steps because they cannot be done in the field. If a replacement part or subsystem requires tuning to work, the tuning can’t be done and the product continues to fail.
Drift
Parts and subsystems typically do not keep their same specifications over time. They drift, due to a variety of factors: age, repeated heating and cooling cycles, wear and tear, even the weather (think of a door in humid weather that causes it to expand). Entropy happens. Replacement parts may not work because the parts they connect to have drifted too far.
Part discontinuance and changes
Manufacturers are constantly changing and tweaking the parts over the lifetime of making a product, in the spirit of continuous improvement. Sometimes the newer versions of the same part have slightly different specifications that work fine in newly manufactured products on the factory floor, which have been tweaked to accept them, but don’t work as replacements for products built in the past. Sometimes parts get discontinued and there either is no replacement, or the substitute part does not work in all the products in the field.
Economics
Sometimes it's just plain cheaper to buy a new unit than repair a failed one. Field repair technicians are typically more skilled, and make more money, than assembly line workers because they have to be able to troubleshoot all sorts of problems. They spend time and money driving to and from the failed unit, and parts needed to be shipped to them, instead of just pulling new ones out of a bin on the assembly line. This all adds up such that repairing a unit, especially when seven attempts are made to do so, is much more expensive than buying a new one.
Finally, my advice:
As a general rule, more expensive products are more likely to be able to be repaired than cheaper ones. This is why you see so many decades-old Harley-Davidsons on the road, and many fewer decades-old, less expensive motorcycles. Harleys are more expensive to buy up front, but they are much more able to be repaired than other motorcycles, especially here in the United States.
If you ever purchase an insurance policy to cover the repairs on a product, pay attention to what the policy says will happen if the product cannot be repaired. You may end up in a dispute with the insurance company as the repair process drags on. Hopefully there’s a way to declare a product dead and get some money to put towards a new one.
Related post: Why your refrigerator won’t tell you the temperature