In the interest of increasing the knowledge base, I'll share a recent problem and solution.
I have a CNX-80 (GNS-480), but it seems possible other GPS's might be subject to the same thing. Some time ago I started getting messages saying "Warning, Loss of Integrity, Cross Check NAV". In the beginning they were intermittent- every few flights it would happen, and the GPS would "recover" quickly. As time went on the warnings became more frequent (most every flight) and the loss lasted longer. Eventually I started getting "insufficient satellites" warnings, where I could bring up the status page and it would be totally blank. In these cases it would sometimes take 20+ minutes to reacquire sufficient satellites. Not good.
Skip to the solution. After a couple of months (VFR...) of head scratching and testing everything I could think of, replacing the antenna cable, and making numerous calls to Apollo support, Stark, and Stein, I started getting low voltage alarms on the EIS. Turned out to be a bad rectifier on the alternator. Maybe others smarter than I could have thought of that, but without the low voltage alarms I'd probably still be scratching my head. It's now been more than 35 flight hours since replacing the alternator, including a trip to OSH and back, with no warnings. I'm pretty confident that the bad rectifier was the cause of my GPS problem.
GPS antennas are powered, in my case by something like 5 volts sent from the CNX-80 through the coax. My guess that the alternator was sending out spikes of AC that were strong enough to knock the GPS antenna off line, breaking the satellite lock and requiring reacquisition.
An additional note- soon after I started getting low voltage alarms (after checking belt tension, wiring, etc) I took the alternator to Autozone for testing ("it's from a 1989 Samurai, sir"
). I had it tested a total of 3 times at 2 stores, each time it tested GOOD. Fortunately someone had a spare that I was able to bolt up for a ground test (sometimes you just gotta love KCNO!)- that was all I needed.
My hope in sharing is that I might save someone else from the kind of frustration I went through on this!
I have a CNX-80 (GNS-480), but it seems possible other GPS's might be subject to the same thing. Some time ago I started getting messages saying "Warning, Loss of Integrity, Cross Check NAV". In the beginning they were intermittent- every few flights it would happen, and the GPS would "recover" quickly. As time went on the warnings became more frequent (most every flight) and the loss lasted longer. Eventually I started getting "insufficient satellites" warnings, where I could bring up the status page and it would be totally blank. In these cases it would sometimes take 20+ minutes to reacquire sufficient satellites. Not good.
Skip to the solution. After a couple of months (VFR...) of head scratching and testing everything I could think of, replacing the antenna cable, and making numerous calls to Apollo support, Stark, and Stein, I started getting low voltage alarms on the EIS. Turned out to be a bad rectifier on the alternator. Maybe others smarter than I could have thought of that, but without the low voltage alarms I'd probably still be scratching my head. It's now been more than 35 flight hours since replacing the alternator, including a trip to OSH and back, with no warnings. I'm pretty confident that the bad rectifier was the cause of my GPS problem.
GPS antennas are powered, in my case by something like 5 volts sent from the CNX-80 through the coax. My guess that the alternator was sending out spikes of AC that were strong enough to knock the GPS antenna off line, breaking the satellite lock and requiring reacquisition.
An additional note- soon after I started getting low voltage alarms (after checking belt tension, wiring, etc) I took the alternator to Autozone for testing ("it's from a 1989 Samurai, sir"
). I had it tested a total of 3 times at 2 stores, each time it tested GOOD. Fortunately someone had a spare that I was able to bolt up for a ground test (sometimes you just gotta love KCNO!)- that was all I needed.My hope in sharing is that I might save someone else from the kind of frustration I went through on this!
