Why does every beginner think they can fix a power supply with just a multimeter?

I swear I see it at least twice a week where someone comes in with a blown power supply and they think poking around with a multimeter is all they need. I had a guy last Tuesday in my shop who spent two hours testing voltages on a dead SMPS and then got surprised when it still didn't work. Dude, you need an oscilloscope to catch that ripple noise and switching spikes, that's just basic stuff. I've been repairing these things for 12 years and half the time a cap looks fine but it's dried out inside causing all kinds of problems. A multimeter won't show you a failing cap under load, you need an ESR meter or a scope for that. Has anyone else seen this trend where people skip the proper gear and wonder why their repairs fail after a week?

3 comments

3 Comments

ryan7938d ago

Multimeter won't catch ripple, that's just facts.

karen_carter8d ago

So how do you even convince a guy who's been fixing stuff for years that his trusty Fluke just can't see that 50mV of noise? I swear some of them act like you insulted their mother when you tell them their meter isn't enough for switched mode supplies. Its not like they need to drop a grand on a fancy scope, even a cheap handheld or a USB scope from Amazon would show them the ripple they're missing. But they just keep measuring DC voltage and calling it good, then wonder why the replacement caps blow up again in a month. Do they think we're all just buying scopes for fun or to look cool on the bench?

jenny_lee8d ago

Just out of curiosity, how many of those guys actually come back a week later asking why their fix already died? I've had a few like that who swore the caps looked fine but two weeks later the same power supply was back on my bench. Did any of them ever admit they needed a scope or did they just blame the parts?