How do you position the test instruments into the circuit ensuring the correct polarity and without damaging the circuit components?

Answer 1

That's a short question with a long answer.

For example, when observing waveforms in a printed circuit card with a 'scope, I like to use a 10X probe with a sharp needle tip. The 10X probe presents about 10 megohms to the circuit under test, so that it doesn't load it, and the sharp needle tip penetrates conformal coatings.

For example, when measuring voltages, use a 'scope set to DC coupling if accuracy is not critical. If accuracy is critical, I use a FET meter or a differential voltmeter, with a sharp needle probe.

When using a spectrum analyzer, various probe schemes can be used. One of my favorites is a sniffer probe consisting of six turns of #30 wire wound round a 50 ohm quarter watt resistor, on the end of a piece of thin 50 ohm co-ax.

For injecting a signal into a receiver, apply the signal across one of the input decoupling capacitors. The capacitor has enough impedance to allow the signal to be seen.

Each case is different, and it up to the technician to know enough about the situation to create a strategy.