I’ve chased seemingly random canbus issues for most of the last year in my G3X system. One has been an intermittent AP disconnect at random times. Never have found the root cause of that. There’s still a case open with G3Xpert on this. There have been intermittent cases of the GMU 11 (can termination point in tail) going offline & showing 100% network error rate in config mode.
After recently having my shop add the GHA 15 to my system while in for a CI, the GMU 11 failure became constant, from the moment I picked it up. (Long story as to why my schedule didn’t allow me to leave it with them then, which would have been the sensible thing to do.) The main symptom is GMU offline, 100% error rate in config mode, with some transient blips in error rates on some of the other devices.
I’ve spent two entire weekends checking connections, voltages, resistance, etc at various points on the bus, and have found nothing. I redid the connections between the Stein-assembled GHA pigtail & the rest of the harness, taking about 12-13 feet of excess length out of the can bus, thinking that maybe the extra length pushed the bus over a tipping point. This didn’t fix the problem.
I went back to square one today, connected to ground power, pulled every breaker in the panel (except PDF), went into config & starting turning breakers on while watching canbus error rates, primarily on the GMU once it was turned on. Long sequence of events (documented ad nauseam in a note on my phone for future reference) led to a smoking gun - I can now reliably reproduce the error. With every single device other than the GAD 27 turned on, there are no canbus errors. As soon as the GAD 27 is turned on, the GMU error rate pegs to 100%.
However, if I go back to only PFD, AHRS2/GMU, AP servos/GMC, and GHA on, and then turn on the GAD 27, there are no canbus errors.
My conclusion so far is that the GAD 27 is producing the errors, but only if the canbus is “fully populated” above some threshold. Does that make any sense?
I’m open to anyone’s suggestions on how to proceed to fix this. I’m tired of troubleshooting & want to get back to flying.
TIA for any help.
After recently having my shop add the GHA 15 to my system while in for a CI, the GMU 11 failure became constant, from the moment I picked it up. (Long story as to why my schedule didn’t allow me to leave it with them then, which would have been the sensible thing to do.) The main symptom is GMU offline, 100% error rate in config mode, with some transient blips in error rates on some of the other devices.
I’ve spent two entire weekends checking connections, voltages, resistance, etc at various points on the bus, and have found nothing. I redid the connections between the Stein-assembled GHA pigtail & the rest of the harness, taking about 12-13 feet of excess length out of the can bus, thinking that maybe the extra length pushed the bus over a tipping point. This didn’t fix the problem.
I went back to square one today, connected to ground power, pulled every breaker in the panel (except PDF), went into config & starting turning breakers on while watching canbus error rates, primarily on the GMU once it was turned on. Long sequence of events (documented ad nauseam in a note on my phone for future reference) led to a smoking gun - I can now reliably reproduce the error. With every single device other than the GAD 27 turned on, there are no canbus errors. As soon as the GAD 27 is turned on, the GMU error rate pegs to 100%.
However, if I go back to only PFD, AHRS2/GMU, AP servos/GMC, and GHA on, and then turn on the GAD 27, there are no canbus errors.
My conclusion so far is that the GAD 27 is producing the errors, but only if the canbus is “fully populated” above some threshold. Does that make any sense?
I’m open to anyone’s suggestions on how to proceed to fix this. I’m tired of troubleshooting & want to get back to flying.
TIA for any help.
