Circuit Breaker Failure
I discovered something last night that I hadn't seen before and thought I would share it here in hopes it will open our eyes to other possibilities as we are troubleshooting faults in our airplanes.
The aircraft owner reported his COMM 2 had failed. It was a King radio that emitted a very nasty odour of burnt electronic components. With this being the case, before installing a new radio I opted to perform a basic power & ground check on the radio's connector. All was well there the first time I measured it, getting nearly 24V as expected.
After installing the new radio it failed to power up. Hmmm... that doesn't look right! Another power/ground check revealed 21V on the power pins. As I watched the meter I saw the voltage dropping rapidly and switched off the master as it went through 19V. Fearing we had some other massive load draining the battery, I worked with the owner to ensure this wasn't the case.
Then it dawned on me... If the aircraft battery was providing a stable voltage, verified with the landing light turned on to ensure the battery actually had good capacity, then perhaps the problem was unique to just that one radio's power circuit.
Sure enough, that was the problem. It took only another minute or two to confirm the circuit breaker, a 10 amp thermal breaker, was flaky.
After removing the old CB I was able to measure its internal resistance which was in the mega-ohm range, varying wildly with even the slightest pressure on the plunger.
I've seen CBs go bad before but hadn't seen one showing that much resistance across its contacts. Needless to say, there's a high probability this faulty CB played a role in the demise of the Comm 2 radio.
Again, just a heads-up. There can be strange things happening in our electrical system, some of them not-so-obvious. It pays to keep our eyes and our minds open as we troubleshoot!
Last edited by Canadian_JOY : 04-16-2015 at 11:07 AM.
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