#90-340

Tech Tips:

Relays can be used for many different control applications, including controlling fans, blowers, other relays, or contactors, valves, dampers, pumps, and much more. A 90-340 is a very common, versatile relay that many techs have on their truck. So, we will use it as an example. A relay is just a remotely controlled switch that […]

Mike Stacey
#90-340 #electrical #relay

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In this short Q&A podcast episode, Bryan answers a listener-submitted question about circuit board troubleshooting: is there a quick way to learn how to check circuit boards, and if so, where are those resources?

A circuit board is a bunch of components put together on a printed circuit board (PCB). There isn’t a lot of helpful universal information about circuit boards available, as they vary quite a bit by model and manufacturer. However, many of the basic components will be the same across circuit boards: microprocessors, diodes, relays, capacitors, and transformers. If you understand what these are on their own, that will help you understand what they do in circuit boards.

You mostly need to know the inputs, outputs, and sequence of operation of a circuit board to diagnose it. The sequence of operation tells you when certain things are supposed to happen, such as in an integrated furnace control (IFC); the flame rectification process is a classic example. If the flame can be proven, the operation continues; if it can’t be proven, then that will cause a lockout (possibly due to improper grounding or poor placement and NOT necessarily because of the board).

A lot of issues with the board can be diagnosed if you understand the inputs and outputs (e.g., 24v signals) or observe it with your senses, such as bloated capacitors or ant nests. Becoming a master of the obvious and checking the manufacturer’s literature are the top two things you can do to diagnose circuit boards.

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