Silver-Conductor Corrosion Can Open a Resistor while Other Visible Corrosion Is Non-Causal

What the evidence preview establishes

Both resistors failed because sulfur corrosion consumed the silver conductor near the termination edges, interrupting the connection to the thick-film resistor element. Separate corrosion of the board-side tin-lead material did not explain the electrical opens.

Why this case matters

Correlate corrosion with the electrical path. An open resistor can result from a narrow silver connection being consumed at a termination edge even when more conspicuous corrosion elsewhere is unrelated; combine surface chemistry with sections that show the conductor discontinuity.