# Question about measuring ESR of capacitors

#### UnnamedUser159

Joined May 3, 2016
501
I see that the element can be on the board but to be 100% sure what i am doing want to ask should the board be powered with its adapter.

I am asking in this case for notebook motherboard

Joined Mar 10, 2018
4,057

#### UnnamedUser159

Joined May 3, 2016
501
I want measure esr. I don't think I have manual. It's cheap esr with lcd from eBay. I will tell model when I am at service

#### Papabravo

Joined Feb 24, 2006
14,693
I want measure esr. I don't think I have manual. It's cheap esr with lcd from eBay. I will tell model when I am at service
Without the manual, how do you know the "cheap esr with lcd from ebay", which tells us essentially nothing, can make the measurement you require? Testing the AC charateristics of a component is not the province of cheap testers.

#### rsjsouza

Joined Apr 21, 2014
263

#### wayneh

Joined Sep 9, 2010
16,401
...should the board be powered with its adapter.
No, not normally. You might get away with it but it would likely interfere with the measurement. The presence of a DC voltage on the cap is allowed for (or certainly should be) but having an AC component there would mix with the applied test signal.

#### UnnamedUser159

Joined May 3, 2016
501
I am still not reading all of your answers but maybe i have more important question :

They are powering the notebook board with its adapter. The questions are:
are they using analogue meter?
What range they use?
What they expect to see to tell "this capacitor is for replacement"

#### wayneh

Joined Sep 9, 2010
16,401
I am still not reading all of your answers but maybe i have more important question :

View attachment 158078

They are powering the notebook board with its adapter. The questions are:
are they using analogue meter?
What range they use?
What they expect to see to tell "this capacitor is for replacement"

In my opinion they are just looking for DC voltage (probably less than 20V) to identify where the power is no longer seen. No sign of ESR testing unless that is written somewhere else.

#### UnnamedUser159

Joined May 3, 2016
501
wayneh thanks.

There are 3 things in this pdf about testing capacitor - one said that esr meters can measure esr without desolding caps, some words about measuring with C-Meter and that with picture was the third one.

The topic was began with questions about esr meter but this with picture was like question 2

#### Mr. Multimeter

Joined Sep 17, 2018
63
Generally speaking, you shouldn't have a "live" power source while measuring those caps.
If you are trying to determine whether the cap is good or bad by it's ESR simply testing in circuit (without power) should suffice if the meter has the capability.