How to check SMD capacitor for being shorted, without disconnecting it from the electric board

This YouTube video shows that you can check SMD capacitors for being shorted using buzzer mode, by touching the ground of the electric board with the negative terminal while touching each side of the SMD capacitors with the positive terminal, the one that has both of its sides making a buzz is identified as shorted.

"SMD bad capacitor test / laptop - desktop computer & electronics troubleshooting"

My problem is that I couldn't identify the "ground" on my electric board.

It's a 2 circuits (AC & DC) board.

P.S: The 2 golden squares near the microprocessor don't exist on my board, the rest is identical to mine.

Also when I checked some of my SMD capacitors using resistance mode, I got the following values:

• 11K Ohms
• 12.4K Ohms
• 11.6M Ohms
• 11.3M Ohms
• 0.L Ohms (after moving upwards to reach 40MOhms, the maximum of my DMM)

What ohm value should be used to consider an SMD capacitor good or bad?

• What makes you think that any of the caps might be shorted? – brhans Apr 30 at 12:40
• Long story short, the exact same error in the washing machine I'm fixing is being fixed by an online video where the problem was in a shorted SMD cap. So I have to start somewhere, right. – Ashraf Alshahawy Apr 30 at 12:46
• Just touch your probes one to each side of the capacitor. The results will be just as (un)reliable as the results in the youtube video. If you measure a short on the capacitor pins, the capacitor might be shorted. It could also be that some component in parallel with the capacitor is shorted. – JRE Apr 30 at 12:47
• There is no appropriate resistance value for a capacitor on a PCB. A good capacitor should be an open circuit (your meter shows 0.L) when measured with an ohmmeter. It might start low and go up to 0.L. But, on a PCB you will be measuring the resistance of all the things connected to the capacitor so all measurements are wrong. – JRE Apr 30 at 12:51
• The only certain way is to remove it from the circuit. The video shows a different circuit than yours so you can't expect the same measurement results. – JRE Apr 30 at 14:18

Without a schematic, you will need to engage in some sleuthing to find the ground plane. A good place to start checking would be the negative (-) pins of the large electrolytic capacitors, which are clearly indicated on the plastic sleevings of the capacitors (the lighter-coloured section).

Using the plated-through-hole mounting pad may or may not work, because they are not always connected to ground. You can check this by measuring between the electrolytic capacitor negative pin and the mounting pad.

You can still take direct continuity measurements across the capacitors. A short is a short.

One final point to remember - these capacitors are almost always connected in parallel with other components in the circuit. A short indicates that one or more of the devices on the circuit have failed short - not necessarily the capacitor.

The most common failure mechanism for ceramic capacitors to fail short is mechanical stress causing the ceramic layers to crack and internally short out. Unless you dropped the assembly, I doubt the caps are bad. If they were exposed to excessive electrical or thermal stress, you would see burning, discoloration, etc.

The measurements you took already - all with some resistance or beyond the DMM measurement capability - imply that none of the circuits connected to the capacitors you checked are shorted. Your problem is likely elsewhere, or different in nature (i.e. not a short).

Where I would start is putting your DMM in DC voltage mode, plug the AC power in and check for DC on the logic board by carefully measuring voltages across the ceramic caps and e-caps on the logic board. DO NOT PROBE THE POWER SUPPLY. If you touch the wrong area you could get electrocuted. Also be very careful to not short your probes together when measuring, or you may get a really big spark.

How to check SMD capacitor for being shorted, without disconnecting it from the electric board

Basically you can't because you are reliant on other components connected to it being non-zero (or even close to zero) impedance and this won't always be the case. And then, what if your buzzer tells you unambiguously that a certain SMD capacitor is short - these capacitors have no marking on them so what do you do next?

I also note that the video you linked has a title with these words: -

SMD bad capacitor test


• Snork. Upvoted for the "bad test." – JRE Apr 30 at 12:52
• Comment vote for using the word "snork". – Andy aka Apr 30 at 12:54
• Next I'm gonna remove it and replace it, or in case of this video that has the same problem as mine, he just removed the shorted capacitor and the washing machine can finally start youtube.com/watch?v=52NltT5C8Es&t=250s In this video he used the diode mode, which begs the question, is this test unreliable too? – Ashraf Alshahawy Apr 30 at 13:41
• @AshrafAlshahawy Any in-circuit test is prone to being affected by other components partially shorting out the component you want to test. – Andy aka Apr 30 at 14:09

Power the board and check the power rails. If one of them is way too low then a short could be the cause. If there is indeed a short, it could be a capacitor, or other component like a chip or transistor. This short circuit will usually not be a very good conductor, instead it will have enough resistance to heat up.

This means you can find it by looking for a hot component.

If there are dangerous voltages on the board (which may happen on a washing machine board as JRE noted in the comments) then you'll have to use an IR thermometer or a FLIR camera if you can get one.

You can make sure there are no dangerous voltages by disconnecting the power supply and powering the board from a bench supply. This will also allow you to measure current. Then perhaps you can simply use your finger to look for a hot component. You can also squirt some 95% isopropyl alcohol on the board, and look where it evaporates fastest.

• It's a washing machine, so stands a very good chance of having any and all parts of the circuit near line voltage. Please do not use fingers. – JRE Apr 30 at 12:58
• @JRE whoops, corrected, thanks – peufeu Apr 30 at 17:32