Resistances measurement indicator on PCB

I am a little confused with these methods.

I understand what is a Voltage drop, but nobody have teach me how to do it, or somebody show me an example, so i cannot do it.

Can you please help me ? The link you provide me did not help me to understand. I need to see somebody do it in action and simultaneously explanation of what he is doing and why.

I have in my mind three kind of these testings. I will describe them and please tell me where i am wrong.

1) With a multi-meter that is capable of measure in miliOhms, checking suspicious components and the one with the smallest value it is the one that have an inside short.

This can be done without a current apply in the PCB.

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2) Voltage drop with help of a Power Supply Unit. We inject appropriate Volts into the PCB, with the +(red probe) of the PSU connected to somewhere in the PCB where can accept Voltages, and the -(black prob) to the GND of the PCB. Then with the multi-meter in Volt range, we measure the Voltages across suspect components. Multi-meter must be capable for readings of milliVolts. The component with smallest value is the defective one.

But in my case, were i have a PCI with 58 (if i remember well) pins on side A and 58 on side B, which (pins) are very very small, how can i detach the probe of the PSU to the pin that is accepted for example the +12V (I know which pin is this because i have an explanation map of a PCI pins). The Ground area on the PCB is easy to attach something to it because it is a big one.But maybe i will work around with it and think of a way to do it.

3) Voltage drop with a multi-meter , only.

When you said to use the diode mode, do you mean the one that bleeps when touch the multi-meters prob together ?

Then connect the +(red) to the Ground and -(black) to the tested component. Which side ? And then we take the smallest reading as the indication of the faulty components.

Does with this method use the GND as the beginning of the current flow, and if the Voltage reading is small or big, this is an indication that we are close or far from the defective component ?

@dorosk yes, its a bit hard to explain. Basically, in diode mode your multimeter send some voltage across that circuit. If you have a short the voltage will be different than what it should b . A common good one would be 0.4 to 0.6 If you have a beeping diode mode, then touch the component contact that you want to test, with that. If it is a continuous beep, you have a short to ground.

I have not checked yet but I am certain there are plenty of Youtube videos out there, that will show you how and what to test.