Will.iam Posted July 28, 2021 Report Posted July 28, 2021 Well as we were climbing out of oshkosh on the VFR departure my garmin 530w, kfc-150 stormscope, kx165, pcd7100 went off then came back on like an electrical short or someone turning of the master switch then turning it back on except i did not lose my garmin 345 or clock or tachometer or fuelflow meter. I thought it was a short but did not smell anything and no circuit breakers popped. Thought maybe with all the rain that night maybe some got where it should not have but maybe the rough grass/ground we had to taxi over could have wiggled a wire lose or worn through some old insulation. I started turning things off to see if helped or not. Since it was intermittent, that was hard to verify. I do know the glitch would also happen when i had the storm scope off kx165 and circuit breaker pulled on autopilot. I then turned on autopilot and kx-165 and turned off the garmin 530w and the glitch happened again. So that was turned back on. I turned off the pcd7100 and didn’t have a glitch for over an hour so thought that was it but when i turned it back on we didn’t get another glitch for over an hour. I remember soneone talking about their push to talk switch/wiring giving them electrical trouble so i tried wiggling all the wires under the yoke but i could not get the glitch to repeat. I dropped off my nephew and his son in OK and flew another hour on home and that taxi takeoff and flight with everything on i had zero issues like any other flight before. Anybody have a suggestion or prior experience with systems shutting off and then back on? hopefully the mooney hive can point me in a direction to try and narrow this down as paying and A&P to find an intermittent problem gets really expensive. As a side note, a weird systems issue i did not know was that when i pulled just the circuit breaker for the autopilot, my altitude selector also goes out. Also i get a nav flag in my HSI for the GPS even though the needle still moves and gives course correction indications so it’s working correctly but has the flag. Seems the autopilot CB is tied to alot more than just the autopilot. Quote
Vance Harral Posted July 29, 2021 Report Posted July 29, 2021 If multiple avionics devices on multiple different circuits are all glitching at the same time, with no breakers popping, that sounds like a problem with the avionics bus voltage, not a problem with any individual device or circuit breaker affecting others. First order of business is to determine whether the affected devices are all on the avionics bus (do they all turn off when you turn off the avionics master?) If so, it's likely something is drawing a heavy load on the avionics bus, and yes it could be a short directly on that bus due to water or a loose wire. If not, then it's likely still the same sort of issue, except it's affecting the main bus (which drives the avionics bus when the avionics master is on). These busses are physically implemented by bus bars behind the circuit breaker panel, so I'd look back there for moisture or loose wires. As for why some devices shut down and others didn't, most modern electronics will automatically shut down if their input voltage falls below a certain threshold, but that threshold varies from device to device. A "lightweight" intermittent short on a main bus can therefore glitch some devices and not others that are all on the same bus. Quote
EricJ Posted July 29, 2021 Report Posted July 29, 2021 A loose ground or bus supply wire may be getting looser. If it was a short there's likely be a breaker or multiple breakers popping, whereas a loose feed or ground just shuts off the load and won't pop a breaker. 1 Quote
MikeOH Posted July 29, 2021 Report Posted July 29, 2021 Finding intermittent electrical issues is my worst nightmare even as a EE. Standard troubleshooting methods just don't apply. My best advice is based on EricJ's very sound starting assumption of a loose ground or feed wire. Turn on the systems that were affected, then crawl under the panel and, working systematically, carefully 'wiggle' wires looking to cause the problem. Obviously, if you can ID the wires specific to the affected equipment that would be ideal. I don't know about yours, but the underside of my panel is nearly all bundled WHITE wires. Good luck! Quote
carusoam Posted July 29, 2021 Report Posted July 29, 2021 See if we can straighten out what we know from the OP’s description… 1) A short, or short circuit… is power escaping to ground… usually a destructive event… often thwarted by a breaker switch opening… no breakers were tripped, no smoke released, things came back on… So… probably not a short. 2) A loss of power has things turning off and coming back on when the power comes back… more on this later… 3) A loss of ground… if a ground was lost, power couldn’t flow through the device properly…. So many devices are grounded individually a major loss of ground for our planes is kind of unlikely… but check those ground straps to be sure… especially the one for the instrument panel… 4) If you have an avionics Bus… their relay system is designed to always supply voltage to the bus… even if the relay fails…. Do you take this bus? 4.5) The European Mooney community has found a specific relay failure that isn’t covered by the fail-safe system we have… so they have an additional method to supply power that needs to be installed after a plane gets to the EU… 5) Did everything that went off get wired to the same bus… find this answer, you have found where to look for the problem… 6) switches and relays can get old and start to malfunction… expect the avionics bus relay is worth checking the health for…. See if it and it’s switch is working properly… A big guess… the relay supplying power to the avionics decided to go AWOL… or got loose wires/bad connections… See what all the failed devices have in common for a power supply from the ship’s wiring diagram…. This probably gets you to the probable cause within minutes… Remember… there is a difference between a short, and power not getting to the devices… Will, see the avionics switch next to the master… That is a good place to start… if you have this switch, you have an avionics bus… find the relay that is attached to this switch… probably in the tail, next to the battery… check to see if you hear a nice thunk when you turn the switch on… you will get two… Master On, the avionics relay thunks once… Avionics On, the avionics relay thunks again… Relays get dirty and fail to thunk properly… PP thoughts only, all stuff I learned getting my PPL… Best regards, -a- Quote
Will.iam Posted July 29, 2021 Author Report Posted July 29, 2021 Thanks for all the tips and suggestions. Will try to work on it later in the week but this texas heat is brutal this time of year. My annual is due in aug so hopefully i can find a way to repeat the short consistently so as to help find it in the annual when they have to open her up for inspection anyways. I do agree it seems like more of power interuptiin than a short. Thought i heard a clicking in the tail section on one of the glitches. There isn’t a circuit breaker type relay in the tail section near the battery is there? 1 Quote
carusoam Posted July 29, 2021 Report Posted July 29, 2021 Be on the look out for the avionics master in the tail next to the battery(s)… But don’t confuse the click of the master with the avionics relay… The master switch sometimes clicks the avionics relay… All covered in my post above… Probably takes having a friend to push the switch while you identify the click… The avionics bus has a bit of knowledge with how it works… if you want to learn this stuff… it is really helpful… Best regards, -a- Quote
Will.iam Posted December 7, 2021 Author Report Posted December 7, 2021 Just an update to this problem that was finally solved. It was the avionics relay that was going. Mooney doesn’t offer the original relay, only a bigger modified one but problem is the bigger one will not fit in the same location behind the instrument panel. So instead the A/P offered to change my avionics switch to a switch/circuit breaker switch this way when that switch goes bad it will be much easier to replace than where the location of the relay was before. Once he took out the relay and put the switch in it’s place i have not had the glitch again so i consider this matter solved and closed. 1 1 Quote
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