Homebrew PCBs

On Thu, 03 Mar 2005 16:53:28 +0000, Lez <lez.briddon@...> wrote:

>
> Am I missing something here, does it measure it resistance when in
> circuit and running?
> Do you the plug/connect the cap into the box and it 'performs a test' on
> it and tells you its resistance? if so do you need to remove one side of
> it from the circuit its in?


in circuit, you don't need to desolder anything.

You should power off the unit, because AC signals on the cap can influence  
the result, but you don't need to discharge the cap, the DC does no harm.

Of course if there are low resistance parts parallel you measure them too,  
but so far that never happened to me.
(the only situation to desolder i can imagine is when you want to find a  
faulty cap in a series of several parallel ones.)

The meter works by applying a small AC voltage of 50kHz across the cap and  
measuring the resistance for this AC current. The voltage is small enough  
not to trigger diodes.
I use the meter to check all caps in a faulty circuit, which takes maybe  
one minute and you needn't replace old electrolytics "upon sight" as many  
suggest. You can also use old stock with less risk if you test them before.


What i found most amazing is that the meter i linked to uses 3V single  
supply voltage with a LM324 and actually works. (I use 2 nicad cells)

ST