The 650/750 have two power inputs that are not internally connected. One is for the "GPS" and one is for the radio. I'm trying to understand the behavior if only the radio power input is connected. As I understand it, the radio will work even without the other power input. But how do you control the radio? Can I assume the screen won't work with only the radio power input? Can you control (and use) the radio through the G3X Touch screen though with only the radio power input?
Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
GTN 650/750 Behavior w/ Partial Power
- Thread starter kirkbauer
- Start date
Hmm, not sure why I missed that. So I'll amend my question -- will the radio work if only the COM input has power, if GPS does not have power?
Secondly, does this mean you can wire redundant power into each of these three inputs? So there are a total of 6 power inputs? Are there diodes between each pair of inputs to keep the power sources isolated?
Secondly, does this mean you can wire redundant power into each of these three inputs? So there are a total of 6 power inputs? Are there diodes between each pair of inputs to keep the power sources isolated?
Carl Froehlich
Well Known Member
I think there is a misundertanding.
There are three antenna inputs: GPS, COMM, NAV/LOC/GS
There are two power inputs: COMM and NAV
Each power input is on two or more pins. This is done as those tiny micro pins cannot handle the current, so they put them in parallel. There are no isolation diodes inside the radio for power. No, you cannot run reductant power.
Next time I’m in the hangar I’ll pull the NAV breaker on the 650 and see if the radio still works. I suspect it will, but with no display.
I never use a G3X, so you are on your own about that aspect.
Carl
There are three antenna inputs: GPS, COMM, NAV/LOC/GS
There are two power inputs: COMM and NAV
Each power input is on two or more pins. This is done as those tiny micro pins cannot handle the current, so they put them in parallel. There are no isolation diodes inside the radio for power. No, you cannot run reductant power.
Next time I’m in the hangar I’ll pull the NAV breaker on the 650 and see if the radio still works. I suspect it will, but with no display.
I never use a G3X, so you are on your own about that aspect.
Carl
There are definitely theee separate power inputs; just wires the connectors for my 750. GPS, NAV and COM (6 pins total). I have the GPS and NAV wired to the same breaker per the manual, but they do have separate input pins.
I too am curious about the behavior of the Com if the GPS/NAV breaker were pulled. I ended up with them all on the same bus so probably doesn’t matter much. Haven’t fired it up yet so can’t test.
To answer your question, yes the COM will work if there is GPS does not have power but the screen will not come on and looking at the unit, there won't be any indication that it is powered on.
As for your second question, I don't believe there is a redundant power in 650 as it is for the GDU 465
I'm sorry, I should have been more clear -- if the GTN is only powered by the COM input, the screen won't work. In that case, can the G3X Touch still control it remotely? I can't find the manual for the GTN750, only the G3X Touch.
No, this will not work.
Not your exact question, but an interesting tidbit on “partial box” behavior. Louise has a 650 in the RV-6, and early in the trip, the screen went blank. She said that she kept hearing calls “on Guard” in the background all the way to Wisconsin, but didn’t have 121.5 tuned in on her #2 comm (which she was using, along with the native G3X for VFR navigation). She did have the Comm 1 monitor punched up on the audio panel. I asked the guys in the Garmin booth about this, and they said that the modular comm radio that is part of the 650 “block” will tune itself to 121.5 if it doesn’t have any input from the control head (which is provided by the rest of the 650, which wasn’t working in this case). So….if you lose the ability to control the comm radio, but it is still powered, it might be usable on guard. Good thing to know.
Yes, Paul is right - quoting from the GTN XI series pilot's guide:
In this context, "the system" is the GTN main board and display.
In this context, "the system" is the GTN main board and display.
