Troubleshooting a RPM signal problem
Such problems started out with very evident and clear symptoms. For this vessel, it started out simply as well. RPM info was not displayed on one of the ECR console monitors. After some faultfinding carried out by the crew members, they suspected that one of the modules was the culprit.
So some workshop evaluation by us revealed that the suspected module might not have been the problem. Customer was informed accordingly. The instruction was to , nonetheless, recondition the module so that we patched up 1 more area of uncertainty.
So it turned out that the problem was indeed not the suspected module as the problem persisted. We boarded the ship to help troubleshoot the problem that was creating quite a bit of difficulty for the engine crew especially when they had to get accurate, real time info on the rpm of the main engine.
Our investigation revealed that the myriad of modules in the entire system did conceal some not-so-straightforward signal flow where tacho info was concerned. There were 2 sets of tacho sensors, sending info separately to different modules in the processing system, and subsequently to 2 different sets of display within the ECR. Easily summarized in this post, but the process of peeling the system layer by layer was anything but.
We managed to find the real defective module, bypassed it and reroute the source info signal from that defective module to another module, then calibrated the rerouted signal to give accurate rpm info. (You can see the potentiometer that was hanging out at the bottom of the picture. That was part of the workaround solution to overcome the defective module. No way to repair it onboard)
Problem was resolved.