dtoelke Posted April 4, 2015 Report Posted April 4, 2015 This is nothing major but it's an annoying quirk on my plane that I'd like to correct if possible. To turn on the avionics, the avionics master switch has to be thrown down instead of up like the master and the fuel pumps next door. It's not a backwards switch because the throw itself indicates that "up" should be the correct direction and the text is right side up. Could this be an issue with the relay wiring (such that it is on with an open switch circuit and off when the circuit is closed). Any other thoughts? Quote
laytonl Posted April 4, 2015 Report Posted April 4, 2015 A couple of ideas. The switch may have three connection points, a center lug, a top lug and a bottom lug. In this case, the wires should be connected to the center and bottom lugs. Another possibility is that the switch is installed upside down even though the switch plate is installed correctly. Lee Quote
Guest Posted April 4, 2015 Report Posted April 4, 2015 If it has the removable clipped on cover perhaps it was installed upside down, hence the switch is backward. Clarence Quote
dtoelke Posted April 5, 2015 Author Report Posted April 5, 2015 I checked the switch today and it is installed correctly. It's a two lead style, and flipping the switch up closes the circuit, yet shuts the power off. I would think the relay must wired incorrectly (thoughts?). Does anybody happen to know where the relay is located and/or how to get to it? Thanks guys. Quote
DonMuncy Posted April 5, 2015 Report Posted April 5, 2015 I hate to poke my nose in where I am ignorant, but I think I remember seeing where someone said that this relay is designed to fail in the "avionics on" mode. As a safety factor so that in the event of failure, you still have avionics. You might consider this possibility as you work through the diagnosis. Quote
jetdriven Posted April 5, 2015 Report Posted April 5, 2015 The avionics master closes the circuit and powers the relay to the open position. Pulling the avionics master c/b actually restores avionics power since the relay rises in the closed position. It's a fail safe idea like Don said. For example, a 1979 Piper Arrow actually relies on avionics power to be supplied through a single switch. Quote
N231BN Posted April 5, 2015 Report Posted April 5, 2015 Technically, the avionics relay is a normally closed relay. When you turn on the master it powers the relay open so the radios don't come on. When you turn on the avionics switch it kills the power to the relay and it closes, turning on the radios. That way if the spring contacts break inside the avionics switch, the radios stay on. Is this a new-to-you airplane or did you recently have the relay replaced? Or perhaps the switch? Quote
Yetti Posted April 5, 2015 Report Posted April 5, 2015 The avionics relay in a 75 F is on the starboard bulkhead about 4 inches behind the panel about 6 inches up. Best viewed when on your back laying on the floor. Looked through the S&M Manual for some information. Have not found it. Quote
Marauder Posted April 5, 2015 Report Posted April 5, 2015 The avionics relay in a 75 F is on the starboard bulkhead about 4 inches behind the panel about 6 inches up. Best viewed when on your back laying on the floor. Looked through the S&M Manual for some information. Have not found it. When I bought my 75F in 1991, it did not have an avionics master switch, only the electrical master. I stuck the avionics master in. Quote
dtoelke Posted April 6, 2015 Author Report Posted April 6, 2015 Technically, the avionics relay is a normally closed relay. When you turn on the master it powers the relay open so the radios don't come on. When you turn on the avionics switch it kills the power to the relay and it closes, turning on the radios. That way if the spring contacts break inside the avionics switch, the radios stay on. Is this a new-to-you airplane or did you recently have the relay replaced? Or perhaps the switch? Ok that makes sense. So if that's the case then all I need to do is flip the switch upside down and hopefully the cover plate can also be flipped. Quote
bradp Posted December 4, 2017 Report Posted December 4, 2017 These threads will help. What you are experiencing is the normal failure mode of the relay. Interestingly enough, there are two sets of contacts in the relay itself and it may be that the relay functions fine but the contacts don't.... you could always have your A&P take apart the relay to see if it's something as simple as cleaning up the contacts with some emery paper. The "OEM" source for the relays is also hidden in each of those threads. You don't need to go through Mooney to buy them at a 5000% markup. Quote
ArtVandelay Posted December 4, 2017 Report Posted December 4, 2017 FFR, where is the avionics relay on a J? Quote
bradp Posted December 5, 2017 Report Posted December 5, 2017 Behind the round engine gauges on the far right Quote
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