Why was the fault difficult to identify?
The two units arrived with different software versions and settings that pointed to different machine functions. A successful bench test therefore did not prove that the cluster would communicate correctly in the actual machine.
Comparative testing
After backing up the firmware and memory contents, I checked serial diagnostics, CAN electrical levels and start-up behaviour on both units under the same conditions.
- backing up flash and configuration contents;
- controlled firmware-version swaps;
- comparing CANH and CANL waveforms;
- cross-checking component and software documentation;
ConclusionThe replacement cluster was restored to the original software version intended for the Tier 2 machine family. The repaired memory contents of the original unit were preserved, while machine-type compatibility remained a separate issue to resolve.
Why this method matters
Because every state was backed up and changes were controlled, each step remained reversible. The information gained during the repair narrowed the fault domain instead of creating another uncertain state.