Question: How do you troubleshoot a switching-mode power supply?

Original Question: How do you troubleshoot and repair a switching-mode power supply?

Answer: Over the years I have had dozens of electronic technicians work for me. By far the best at troubleshooting switching-mode power supplies had a very simple approach. He looked at it. Under a magnifying stand with good light he examined the circuitry with infinite patience. What he was looking for were opens in the conductors, open fuses, shorts, bad solder joints, signs of overheating such as discolored components, circuit boards, melted solder joints, etc. Suspicious areas were checked with an ohm-meter or continuity checker. Before ever applying power to the circuitry, he found 80% of the problems.

"One of the most effective methods for troubleshooting electronics is unplugging power."

The most effective troubleshooting/repair tool available for computers or microprocessor-controlled systems is turning power off, waiting a period of time, and turning power back on.

Here’s why it works:

Computers and microprocessors are control systems which are generally not fully controllable. This means that either the hardware or software can put them into a state where normal control inputs have no effect on the system. This topic is called “Controllability” in formal Control Theory jargon.

"And if the power supply is not designed properly, it may well attract too much attention by not working." -- Ed Walker

"Power supply layout is as important as any other design consideration. The power supply engineer must be involved in parts placement and routing." -- Robert Kollman

What I said in How To Design a Power Supply applies to how to layout a power supply. There is an near infinite number of ways and if left to their own devices a new designer will usually do a poor job of it. For these designers, Papers like Topic 4, Constructing Your Power Supply - Layout Considerations, in the Texas Instruments 2004/05 Power Supply Design Seminar is highly useful.

My favorite quote from the author, Robert Kollman, is actually the summary at the end of the paper.

"Power supply layout is as important as any other design consideration. The power supply engineer must be involved in parts placement and routing. An understanding of AC and DC parasitics, grounding and cooling makes a successful design."