Fault Diagnosis

Fault diagnosis in horology is a process of elimination that moves from the least invasive checks to the most invasive, and from the most statistically common causes to the rarer ones — much like diagnostic reasoning in any mechanical or medical field. The first questions are always about power and history: was the watch fully wound? When was it last serviced? Has it been dropped, exposed to moisture, or worked on before? Most stoppages in mechanical watches trace back to a small number of causes: a run-down or broken mainspring, gummed or dried lubricant, a bent hairspring, a foreign object jamming the train, or magnetism.

Magnetism deserves particular mention because it produces a very specific symptom — a watch that runs, but noticeably fast, sometimes dramatically so — caused by hairspring coils clinging together magnetically and effectively shortening the spring's active length. It is diagnosed with a simple compass test or a dedicated demagnetising check, and corrected (if that is the sole fault) by demagnetising the movement, making it one of the few faults a watchmaker can sometimes resolve without disassembly at all.

A timing machine — a microphone-based device that listens to the escapement's ticks and displays them as a trace — is central to modern diagnosis because it turns the sound of the escapement into readable numbers: rate (fast or slow, in seconds per day), amplitude, and beat error. A trace with low amplitude but correct beat error usually points toward a power or lubrication problem; a trace with high beat error but reasonable amplitude points more toward a hairspring-stud or roller-jewel position issue; an erratic, unstable trace often indicates something intermittently obstructing the train or escapement, such as a hair or a displaced part.

Symptom and cause do not always map one-to-one, which is why diagnosis is a skill rather than a lookup table: a watch that stops intermittently could be a nearly-broken mainspring, a loose cannon pinion catching the hands, an unclean escapement, or a hairspring coil occasionally touching the balance cock — and distinguishing between them typically requires observing the watch running, under magnification, sometimes over multiple winding cycles, alongside the timing-machine trace.

As with the other Intermediate lessons, the purpose here is to make an owner a better-informed party to a service conversation — able to describe symptoms precisely, understand what a timing-machine printout means, and ask an informed question about what a watchmaker found — rather than to enable self-diagnosis that ends in unnecessary disassembly of a watch that might have had a simple, non-invasive fix like demagnetising.