How Do You Repair a Board?

Circuit boards are just as vulnerable as any part of an HVAC system. They can fail for any number of reasons over time. Everything dies eventually. Now, the question is, you can repair just about anything with enough work. You can remake the windings in a shorted motor or alternator with enough patience. If we throw money, time, and talent at a circuit board, how do we repair it?   The contents of this post are for informational purposes only. We want to highlight the work that goes into repair. Have a professional repair your circuit boards. We are not responsible for any consequences of you doing your own repairs.   Some Basic Concepts All the parts on a circuit board are interconnected in a very specific way. Connecting them any other well will make them short out and do nothing useful. For example, imagine we have a little computer chip. It has 8 little legs, called Pins. The first pin on this chip will turn a screen on and off. The next leg will control a relay for the furnace. The next two are for a button. There’s two more for a temperature sensor. Lastly, two pins are for power and ground. We need to wire this chip into all these components somehow. On the one hand, we could plug in wires or solder wires between everything, but that will quickly become a rat’s nest of chaos. Just soldering […]

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Why Do Electronics Fail?

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 […]

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Why Isn’t There a Relay in This?

Relays are known for the bigger switching jobs, but they’re not the only game in town. There is a middle-ground where your five volt control board would fry and where a relay would be overkill or too slow to do the job. We turn to another special component for these “higher” but not necessarily “high” voltage jobs.   The Relay’s Weaknesses There are jobs where a relay just isn’t the answer. Relays come with two pretty big weaknesses: they’re mechanical and they’re slow. If we were to take apart pretty much any relay, we’d find perhaps some springs, an electro-magnetic coil, and some contacts. Whenever we actuate that relay, parts inside of it move. Moving parts are bad for speed and reliability. Eventually, the switching mechanism, contacts, or actuator inside that relay will degrade and fail. At the same time, we can only force that relay to move so fast. If the contacts inside are a half-inch apart, then we need to cover that half-inch before power will pass through. It’s a small distance, but consider that standard AC power in the US runs at 60hz. If we wanted to change the relay position based on the electrical frequency, it would need to move in 1/60th of a second. We need to accelerate to 2 mph and stop within 16 milliseconds, and that still costs us an entire 1hz cycle. Even then, chances are it will take longer to de-actuate. […]

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High Voltage in AC

Your air conditioner (and whole HVAC system) are a strange mix of parts. On the one side, we have low voltage, DC electronics that couldn’t tickle a fly. On the other, we have high voltage, AC equipment that could turn an ill-prepared reptile or rodent into a charred chunk of bones. How exactly do we mate these two, different systems together safely?   The Safety Issue In all electronics, we strive to separate high voltage and low voltage. We don’t want them to touch each other. In some systems, you have no choice but to put high and low voltage equipment on the same board, in other cases you try to keep them on separate boards altogether. If there’s any sort of electrical short between high voltage and low voltage, the low side is going to get destroyed. That’s your best case scenario. 240 volts or 440 volts blasting into some tiny microprocessors and capacitors, which then explode in a terrifying, but mostly harmless show of pyrotechnics. If the board is really well built, a diode will take the brunt of the failure before anything scary does. Sometimes though, these shorts don’t go like that. Some older equipment or equipment which never passed any reviews like Underwriters’ Laboratories can send high voltage straight to frame components, a button, or other areas where a user could come in contact with it. 220 Volts is not a pleasant experience, let me tell […]

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What is a Microcontroller?

PLC’s are not the only solution to automation. They go up against devices called Micro Controllers, which are often far cheaper, but yet essentially the same. Let’s get under the hood with what exactly a micro controller is.   A Barebones Device Microcontrollers are designed almost like computers from the 80s. They’re barebones devices, sometimes with processors running at megahertz and less speeds and just kilobytes to a few megabytes of ram. These are numbers more comparable to an old Gameboy than a computer or even your cell phone. This sounds really useless, doesn’t it? How do you use something so ‘primitive’? Simplicity is the key here. On a desktop computer, there’s millions of lines of code running. It can take multiple chunks of a millisecond to process and so something. It takes hundreds of watts in a day, just to sit there idling. A regular computer is incredibly powerful, but it gets in its own way when it comes to processing interactions. The complexity and speed ironically slow it down. In order for you desktop to respond to a keypress, the keyboard input has to be sent, decoded by hardware, passed to a driver, interpreted in the kernel, handed off to a program in the user end of the operating system, calculations performed, and then work sent back to the kernel, to the hardware, to encode instructions, to actually do something. For a microcontroller, an input comes in, is […]

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