Part Failure Vertification: A-B-A Swap Method


Sometimes, a board will suffer from a sudden failure in operation, like no power output, no motor rotation, etc. It can then take quite some time to verify which components are causing this failure if you start testing at random.

Here’s a simple method that can help us verify where the failure is occurring in our system - the A-B-A Swap method.

The A-B-A Swap Method is a simple cross check test, which can confirm the observed issue is not systemic.

  • A-B-A Swap Method
    (1) Remove the suspected component (A) from the original failing board.
    (2) Replace the suspected component (A) with a known good component (B) and check if the original board now works properly.
    (3) Mount the suspected component (A) to a known good board and see if the same faliure occurs on the good board.

Step 3 is important because it helps us to exclude any possibility that the issue is caused by a systemic issue or the interaction of multiple slightly bad components on a good board.