Distinguishing SDI Carrier Detection from Reclocker Lock

An SDI status pin can indicate that energy is present on a cable without proving that valid video is being recovered. Equalizer detection, reclocker lock, and downstream payload validity describe different stages. Keep those observations separate when a receiver intermittently loses picture or reports a cable connection that does not produce usable data.

Decode the actual status configuration

The TI LMH1219 data sheet describes configurable status outputs and separate indications associated with signal detection and reclocker operation. Some status behavior depends on configuration and read or clear semantics.

Record the register settings behind each observed pin. A net named LOCK on the schematic does not establish what the device currently drives there. Check whether firmware changes that function during initialization.

Build a stage-by-stage observation

Capture input presence, equalizer state, reclocker lock, selected data rate, and downstream error information where available. Timestamp changes so a brief lock loss can be related to a visible video disturbance.

Distinguish a persistent state from a latched historical event. Reading a clear-on-read indication can alter later observations, so define the polling and logging method before comparing repeated trials.

Control the physical channel

Use a known source and documented cable type, length, and connector arrangement. Check the intended impedance environment and remove unnecessary adapters for the initial test. Cable length alone does not completely describe loss or connector quality.

For example, compare a short known cable with the installed path while keeping the source rate and pattern fixed. If carrier detection remains stable but reclocker lock changes, preserve that difference rather than collapsing both results into a single cable-present flag.

Follow the first failing stage

If input detection disappears, investigate source output, cable continuity, connections, and input configuration. If detection remains but lock drops, examine supported rate selection, input quality, and clock recovery conditions.

If lock remains stable while the downstream receiver reports errors, investigate payload interpretation and the path after the reclocker as well. A recovered clock does not validate every subsequent data-processing step.

Repeat relevant source changes, reconnects, and temperature conditions. Record whether automatic rate detection or forced-rate settings are active. A forced setting that works for one format can fail when the source changes format.

Save the status-function map, channel description, time-aligned events, and downstream validation results. The completed diagnosis should identify the earliest stage whose behavior becomes inconsistent with the expected signal. That evidence provides a clear next action and prevents a convenient status pin from being mistaken for proof that the complete video connection is healthy.