Your HVAC system has countless little controller boards and electrical components driving it. There’s the boards in your thermostat, furnace, and in some cases even in your pumps, just to scratch the surface. These boards do all burn out eventually, but the weird thing is that, there are no moving parts in them TO burn out. What’s going on?
Anatomy of a Circuit Board
Let’s take apart one of these circuit boards and see what’s going on. The backbone of this whole thing is the PCB, Printed Circuit Board. This is that flat chunk of plastic that everything else sits on. It’s the thing you normally hold in your hands. These boards are basically copper and plastic, that act as wires, connecting multiple parts together. There’s traces of copper on the board that go from one item to the next to the next.
PCB’s are pretty long-lived, but they have their weaknesses: chemicals, voltage, and physical stresses. If there’s too much power going through one part of the board, such as from a power surge, it can blow out one of the traces. If there’s anything at all corrosive that leaks onto the board, it’ll eat the traces or even eat a component of the board itself. Sometimes, this even happens from components on the board themselves, capacitors and batteries can leak corrosive fluids that will cause complete failures. In retro electronics, it’s actually pretty common to “re-cap” a board to avoid such failures. Vibration and bending can also cause solder joints to fail and for components to come off the board or for traces to be broken. Once any of these things happen, power and data doesn’t flow from component to component like it should, the board can’t carry out it’s function.
On top of the circuit board go all the actual parts that do the work: diodes, resistors, capacitors, logic and memory chips, and everything else under the sun. Most of these are pretty long lived. Diodes, resistors, transformers, and other equipment are known to be sturdy and reliable. Capacitors… not so much, they’re known to leak or explode if there’s any defects in manufacturing.
The real trouble though, arises from the memory chips. These Integrated Circuits are in many ways like PCB’s inside, they have multiple components all wired directly together. The key difference is that these parts, processors, memory, etc, are made on nanometer-scale processes with silicon. They’re sensitive to heat, power, and even wear over time.
IC’s Can Wear?
In a matter of speaking, yes. The issues with integrated circuits all occur on the molecular level. We push electrons back and forth, triggering gates in transistors and memory storage circuits. Over time, electrons can get stuck in these logic units, causing microscopic switches to essentially become stuck in one state or another. We can push in more voltage to help drive the electrons around, but at some point, the charges become so built up, that we can no longer reliable measure or control them, in parts of a chip.
What this leaves us with is that even the most robust part of a circuit board, a part with no moving parts, actually does have some moving part inside it. It’s just a microscopic moving part. Over time, the changes in electrical charges will wear down these little chips. It’s not so visible in processors, but it’s impossible to miss in memory chips. Have you ever had a flash drive die? This is why. The storage parts of it just give out.
What Do You Do?
When one of these boards fails, there’s generally two options: replace the board or repair the board. In about 95% of cases, it’ll be better, cheaper, and faster to replace the entire board. There are however, exceptions to every rule. Some boards are particularly expensive or are rare as older parts go out of manufacture and then out of stock. The actual components on the boards themselves aren’t even all that expensive. Some parts literally sell for less than a penny.
Boards using stock, off the shelf components are the easiest thing to fix. A specialist can diagnose the board, locate a replacement component, desolder the old one, solder in a new one, and get things back on track for just a few hundred dollars. There are however, cases where a manufacturer will use custom parts, specialist, custom chips that cannot be ordered alone. In these cases, the only way to do a repair is to find another broken board and take donor parts off of it.
This is a lot of work, but as we said, when you’re looking at a possibly $3000 circuit board, it might pay to have a specialist repair it. When you’re looking at a $3000, out of manufacture and out of stock board, then it pays to have a specialist repair it, otherwise you could be staring down a complete system replacement.