Error Appeared Right After Servicing: Board Locked, Not Dead

An error appearing immediately after a service visit, on equipment that ran normally beforehand. Power was interrupted at the unit during the work. The system behaves normally in every respect apart from the displayed error.

A system behaving normally while showing a fault is the pattern that separates a record from a condition. If something were genuinely wrong, the behaviour would show it. What produces a display without a symptom is a latched state, and the commonest cause of one is an interruption at the wrong moment, which is exactly what a service visit provides. That makes the sequence of the visit more informative than any test.

Control boards latch certain states so a fault cannot be hidden by the system simply restarting. Cutting power at an unexpected moment can leave the board holding a state it was never told to release, and it keeps displaying that state indefinitely because nothing has instructed it otherwise. The equipment is entirely healthy underneath. The display is reporting a moment rather than a condition.

A full reset is carried out to the manufacturer's procedure, which clears the stored state and returns the display to normal. It is worth being clear about what this is and is not: a reset is a legitimate answer to a latched state and never a legitimate answer to a live fault. Anything that returns after a proper reset was a condition, and it needs finding rather than clearing again.