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SL30 Remote Nav List error

BMcCand - N248CT

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The SL30 Nav-Com receives remote frequency lists from the GPS396 via HS34 interface in my plane. After about 30min

of operation, the Nav selection list becomes incorrect. The listed frequencies are for COM, not Nav.

The big knob does nothing, the small knob cycles through App, Twr, Atis, Gnd for a nearby field.

This all works correctly @ pre-flight and the first 30 min or so.

I think this is a thermal problem. I'll be stopping by Garmin in Salem to examine it.

I power-cycled the radio to see if a memory failure would be noted at startup, no problem.

I have not yet pushed ENT to see what the Nav logic does with a Com frequency value.


Manually setting standby Nav frequency continues to work. Sending a standby Nav from Gps Vor page works.

I checked the GTX327 setup pages after landing once, got a Unit temp = 100, LCD temp = 98

but I don't know the units of measurement. This occurred in both cool and warm flight

conditions, I don't think cabin heat is contributing, but will examine hoses behind panel.


I don't have a laptop in the plane nor a handy flight engineer to send queries to the SL30 ADC while flying.


Has anyone else seen a problem like this? (the radio problem, not the lack of an engineer !)

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  • 3 weeks later...

I did more tests per request. The flip-flop <-> button will put a COM frequency

into the NAV display; it then flags. Pushing ENT will put a COM frequency

into NAV standby, but then turning a knob will jump the frequency back into

the legal Nav range.


I was on the west coast, so took the radio to Garmin at Salem. They said they never

saw this problem before. After 4 days of heating/cooling the radio and shaking it,

and not duplicating my problem, I decided to pay for a new circuit board.

I haven't flown with the radio yet, so I don't know if the problem is solved.

If not, I'll add an RS232 out fixture and write some logging software to capture the

GPS396 data fed into the radio through the HS34.


This is one of these "interesting problems." I'll call Dynon to see if the HS34

does anything more than echoing serial input messages to the SL30 and D100.

If the GPS396 has failed, I'll probably ignore the failure for a while, then

get a GPS496 as the 396 has been declared obsolete. But I have 11 months more of data

for the 396.

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