Hi,
thanks for your answers.
I read many articles about in-circuit testing. The most important one is the following by Teradyne:
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Here are some important points:
1) It is impossible to distinguish 2 capacitors in parallel: the test will measure the sum of the two.
2) In-circuit tests are carried out on UNPOWERED targets. In words, ATE systems DON'T power up the boards during the test.
3) Probe signals have an amplitude of 0.2 Volt, in order not to power the IC's that are loaded on the board.
4) Some components can be tested by DC signals, others require AC signals (a sine wave at a certain frequency).
5) The polarity of Electrolytic Filter Capacitor is an issue. I'll post a thread as soon as discover how to test it
6) A good ATE system may cost from 30.000 to 50.000 USD
ciao, Enrico