If you own a Garmin GTN 650/750 or GNC 255A, there is a new mandatory service bulletin that must be accomplished (if your unit is within certain serial number ranges).
PURPOSE
An issue has been identified where the affected units may present incorrect VOR or Localizer deviation information. This may be indicated by an unsteady (wagging) CDI and can result in a steady incorrect offset for up to 30 seconds.
COMPLIANCE
Mandatory for affected GTN 650, GTN 750, and GNC 255A/255B units to be accomplished by July 31st, 2014
The SB contains the list of affected serial numbers. The unit must be sent back to Garmin for installation of the modification by July 31st 2014 or this modification will not be covered under warranty.
there is a new mandatory service bulletin that must be accomplished
Only if you want a warranty.
Only if you want a warranty.
Which I mention 5 lines further down and which everybody with these units will want because you certainly do not want to have a “wagging” CDI. In the typical corporate euphemist terms this probably means that the CDI is completely off driving you into a mountain.
I did not comment on whether it did make sense or not.
It’s just that whenever I read
there is a new mandatory service bulletin that must be accomplished
that activates a certain sensor with me… 
I might scale down my search for an illicitly sourced unused GTN750, for a few months
Presumably the SB is a software upload and is FOC?
If it was a software update, it would not have to be returned to Garmin.
If it was a software update, it would not have to be returned to Garmin
Of course you are right, that is obvious now I stop to think! But despite being wrong on that, I still think it will be FOC, due to the note about it needing to be done by July 2014 to qualify for warranty
They are trying to be quick to not get an AD slapped in their face.
There seem to be some good reasons as to why the 430/530 family is still very popular. ;-)
