When a circuit stops working it can be hard to know where to start. Sometimes the problem is simple like a loose connection or a power supply issue.

I usually think it makes sense to check the basics first before replacing any parts.

What do you normally check first when troubleshooting a circuit? Do you start with the power supply and connections or use a multimeter to check the signals?

I’d be interested to hear what works best for others.

 

You don’t begin by replacing parts. You locate the problem first.
There is no single solution to cover all cases.

This is where you become a detective in solving a murder mystery.

You start with a conversation with the owner. Learn about the history of the appliance, age, usage, circumstances, for example, water damage. What were the conditions leading up to the failure.

Next comes a visual inspection, look, smell, touch (while unit is powered, or use a thermal imaging camera to locate hot spots, after you have done the first things below).

As you said, start with the simple things first, fuse, power cord, plugs, switches. A very common failure point is the power cord at the neck of the plug or socket.

The testmeter is used to check for AC voltage coming in and DC voltages at the power supply (assuming that it is DC powered).

 

When a circuit stops working it can be hard to know where to start. Sometimes the problem is simple like a loose connection or a power supply issue.

I generally start with the power supply following a good visual inspection. Obviously start with any fuses or disconnects like breakers. Really depends on what I am troubleshooting.

Just My Take....
Ron

 

an important step is getting familiar with the product. often no schematics is available so one is forced to make a substitute - either hand drawn circuit or mental image of what the circuit is and what it does - by identifying key components.
one does not go blindly and start probing things at random - first you try to understand the circuit, then make a prediction of what values are reasonable at certain points, then measure at those points and compare measurement with prediction.

say you are troubleshooting AC outlet that should measure some 120VAC. you expect 120VAC (that is prediction). then you measure and see 117V or 121V or similar. this is close enough to declare it ok.
but if you measure 69V or 237V, something is way off. one would not know if that is ok unless we had expectation (prediction) what the value is supposed to be.
everything that we measure is based on some prediction (knowledge/expectation or previous experience).
and it goes beyond that. before making measurement, one should be able to also make the next prediction - what could be wrong or what should be measured next if this measurement is not matching prediction.

for example you are about to measure voltage on that 120VAC outlet. you know what to expect (one prediction). but you should also be able to tell what the next step should be (before you measure) what the possibilities or options are if the measurement is too low, or too high.
if the voltage to be measured is too low, chances are that there is a loose connection somewhere causing voltage drop and low reading.
if the voltage to be measured is too high, something is injecting higher voltage into circuit. there must be source of higher voltage present and path for current to leak into whatever circuit you are testing.

this is how you build a path to be followed till root cause is uncovered.

 

Depends on the circuit.

First thing to check is if it's receiving power or not, then a visual inspection, as Ron has already suggested. Then check if it has warm spots. And then comes the interesting part, for instance if it's a digital circuit, is its oscillator doing its thing? ... if it's analog then an oscilloscope is an indispensable tool.

Diagnosing a circuit is more an art than a trade, IMHO

 

Fuse. IF blown - why? What caused it?
If not the fuse, power. Is there power?
Visual. Does there appear to be any visible damage? If so - don't just start replacing things. Something caused the problem which may have manifested itself as a blown component.
FULLY DIAGNOSE THE PROBLEM before you start throwing parts at it.
Once you have eliminated the fuse and power supply you start looking for places where an interrupt may have occurred. Check the solder for fractures or cold solder joints. Frequently enough the problem can be a bad solder joint. I was given a TV with a Horizontal Control issue. I reflowed all the solder joints having to do with HC and that solved the problem. There was nothing visual that lead me to that - other than the horizontal was restricted to 1/3 of the screen.
Beyond the basics what you do depends on the circumstances that has lead to the failure. Does it make a sound? Is there a light? From there it becomes far more focused on the type of circuit you're working on. Tracing down an audio problem in a stereo is different from fixing a kids toy, or a computer. But throwing parts at what you believe is the issue may be a result of a true fault, one you haven't detected yet. That's why you fully diagnose the problem before you start buying and replacing parts.

 

"Is is plugged in, is it turned on, is the brightness|volume|whatever control turned up?"

 

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