# Completed demonstration example — beacon with two faults

This is one fictional nine-volt beacon throughout the attempt. Its published case card allows multiple simultaneous open faults. The assigned browser and campus lab instead introduce exactly one fault at a time.

## Initial evidence and first diagnosis
With power on, source / fuse output / cable output / lamp supply read **9 / 9 / 0 / 0 V** relative to the common return. The lamp was dark. The first missing supply supported an open cable. The unpowered lamp's own condition remained unresolved; the readings did not prove it healthy.

## First repair and failed whole-system check
I isolated the source and replaced the cable only. After restoring power, the trace became **9 / 9 / 9 / 9 V**, but the **same beacon stayed dark**. The repair successfully restored supply without resolving the original symptom. I preserved both statements instead of calling the cable diagnosis wrong or declaring the job complete.

## Second diagnosis and repair
With healthy supply and a dark load, I isolated power and tested lamp continuity. The result was **open**. I replaced that confirmed open lamp while isolated, then restored power. The supply remained **9 / 9 / 9 / 9 V** and the lamp lit.

## Preserved diagnostic chain

| Stage | Supported finding | Action | Verification |
| --- | --- | --- | --- |
| Initial trace | Open cable; lamp condition unknown | Isolated cable replacement | Supply restored, light still absent |
| Same beacon after first repair | Healthy lamp supply, dark output | Isolated lamp continuity test | Open load confirmed |
| Confirmed second fault | Open lamp as well as the earlier cable break | Isolated lamp replacement | 9 V supply and visible light |

## Reflection
My first diagnosis was useful but incomplete. Assuming it explained the entire symptom would have stopped the investigation too early. The failed output check changed what I needed to test, without erasing the evidence that justified the cable replacement. In a new case I would read whether its rules permit multiple faults, diagnose from its own trace and check the original symptom after every repair. This example does not establish that the assigned one-fault circuit has two defects.

## Limits
These are idealised authored model readings, not measurements from constructed hardware. A continuity check is performed only in the model's isolated state. The record establishes this fictional apparatus's behaviour and does not certify work on an arbitrary physical circuit.

Named output: circuit-diagnosis. Assistance: complete narrated worked example.


## Method to carry forward

Repair only what the evidence supports, then test the original symptom again.

This example has two simultaneous faults; the assigned model has one. Use its observed trace, not this cable-and-lamp answer.

The complete example explains one defensible approach. In your own challenge, select observations and tests from the supplied rules, keep your prediction separate from the result, and justify both the checks you perform and those you omit.