G1000 - "Ghost" NAV radio volume level decrease

[MatthiasArnold]

Dear MS brain,

On yesterday's flight, while trying to monitor an ATIS message that is only broadcasted via VOR, I observed a strange problem:
Whenever I tried to increase the NAV audio volume by turning the VOL/ID knob clockwise, the audio volume automatically dropped to 0% within some seconds once I stopped turning the knob. Like a little "ghost" sitting inside the G1000, permanently turning the knob counter-clockwise..
I tried it with PFD & MFD NAV VOL/ID knobs - same behavior.
So I ended up fighting the "ghost" by permanently turning the knob CW while monitoring the ATIS message (resulting app 20-30% audio volume as long as I did not stop turning). Since I was flying in hard IMC, I didn't dig deeper, but was happy once I copied the complete ATIS. 

Any ideas/thoughts on the root cause of this strange behavior and how to fix it?

Best,
Matthias
 

 

[Will.iam]

Don’t know if knob is digital or mechanical, but if mechanical deoxit will clean up the contacts. 

[LANCECASPER]

On 9/10/2022 at 11:25 AM, MatthiasArnold said:

Dear MS brain,

On yesterday's flight, while trying to monitor an ATIS message that is only broadcasted via VOR, I observed a strange problem:
Whenever I tried to increase the NAV audio volume by turning the VOL/ID knob clockwise, the audio volume automatically dropped to 0% within some seconds once I stopped turning the knob. Like a little "ghost" sitting inside the G1000, permanently turning the knob counter-clockwise..
I tried it with PFD & MFD NAV VOL/ID knobs - same behavior.
So I ended up fighting the "ghost" by permanently turning the knob CW while monitoring the ATIS message (resulting app 20-30% audio volume as long as I did not stop turning). Since I was flying in hard IMC, I didn't dig deeper, but was happy once I copied the complete ATIS. 

Any ideas/thoughts on the root cause of this strange behavior and how to fix it?

Best,
Matthias
 

 

Depending on the age your knobs may be cracked and need replacing. Sarasota Avionics sells individual knobs or the set. (https://sarasotaavionics.com/avionics/g1000-knob-replacement-kit)

[MatthiasArnold]

Resolved (root cause detected)
Thank you all for your replies.

• Good to know where to purchase replacement knobs once they are brocken or get sticky by age.
• Although I utilize contact cleaner for things like microswitches and connectors, I'm a litte reluctant to apply it directly to the GDU, at least for the time being  

Meanwhile I had the chance to investigate the behavior on ground.

General 
Per my understanding of the G1000 system architecture, the actuation of the VOL/ID knobs/encoders in the GDUs are processed by the respective GDU electronics/firmware and the result (increase/decrease level) is then forwarded to the GMA which does the internal audio processing for the G1000 system (mostly digitally). By whatever means (e.g. digitally) the resulting audio level setting (in percent) is somewhat synced between the GMA and the GDUs, otherwise the other GDUs in the system would not be aware it.

Behavior (isolated operation of PFD/MFD)

• The NAV VOL/ID knob at the PFD behaves erratically. When turning in CW, almost any incremental click is followed by a decrement. Depending on the position it even may result in decrements.
• The NAV VOL/ID operates as expected

Behavior (parallel operation of PFD/MFD)
When the NAV VOL/ID knob on the PFD stays in a static position the volume can be easily set via the knob on the MFD (as long as the knob on the PFD is not touched). With the right hand it is easier to operate the knob on the MFD anyways.

Hypothesis

The encoder (and/or electronics) of the PFD's NAV VOL/ID knob is malfunctioning.
Typically when actuated an encoder creates two phase-shifted rectangular output signals per click (phase shift (maybe its should be named angular shift) utilized for detecting  direction of turn). I deigned in and interfaced encoders in the past - the observed behavior can be caused if one one of the two output signals is degraded and as such the direction of turn detection goes havoc.

So - no "ghost" - probably only a worn encoder..

Best, 
Matthias