I use this circuit when I troubleshoot electronics products for many years now and I think it is a good idea to share it with you. The original author could be found at the link bellow:
Things you need to make the circuit:
8 pcs diodes : 1N4007 (choose any diode depending on your requirements)
2 LED (different colors)
2 Resistors (100K and 100 ohm)
probes (2 pcs with different colors)
Isolation tape or you might build it in another way.
No matter, which polarity you connect the probes. It will works. The different LED color will indicate the direction of the current. Download the LTSpice file to see how the circuit works.
1- I am not responsible for any damage, or bad usage of the circuit. You should know what you are doing before building this circuit. You need to be a professional electronic technician to build this circuit. Capacitors could save a large amount of energy and a high voltage as 1000 V!!!
2-I am not the author of this circuit. I am not the designer of the circuit. I found the circuit to be useful and I made it for myself.
3-I wrote the LTspice circuit to analyses the circuit. That part is mine and you can download the file free of charge.
Step 1: Build the Circuit
1) First build your circuit. You don't really need any kind of PCB. You can
solder the diodes together and isolate them using what ever you have (plastic pipe, Plastic Heat Shrink pipes ..etc) and cover all parts so you don't touch the components in any way.
Step 2: Make the Probs
2)Make two probes and solder them to the components as in the circuit shown. The probes could be a
CROCODILE CLIP-INSULATED or what ever you choose. It is good to have one side a CROCODILE CLIP-INSULATED, which will make it easy for you to connect the discharger to the capacitor, when you probe around different capacitor to discharge them.
Step 3: Usage
Connect the capacitor to the probes. If it is holding charges, one of the LED will lights up. Depending on the direction, the color of the LED will be different. Wait tills the LED will turn off totally.
At this time, the capacitor is discharged totally and should be safe to deal with.
Read the datasheet for the diode to know how much voltage the diode could deal with in both directions.
Please don't hesitate to put questions if you have any.
Thanks for watching.
Note about the LTSpice file:
You need to use my (standard.dio) which has the diode definition. Make a backup for your original (standard.dio) file and then replace it with my file. There are several other diodes were defined in this file.
You find the file in your LTSpice file under "/cmp" folder.