They need to put an oscilloscope on the connection between the voltage regulator and the field winding. Without that, they haven't got a hope.
If that is clean, they need to apply a smooth voltage to the G1000's bus voltage logging input and do a short recording...
Do you have any other instrument which might be logging (or displaying) the bus voltage?
But in any case it's trivial to do a ground run, or even a flight, with an oscilloscope on the 28V bus. The one in the first picture here is all you need.
they serviced the connector (whatever that means)
You could try that as a novel chat-up line next time you go clubbing in Prague 
Yes, they used an oscilloscope! Since my electrical qualification is only high enough to change light bulbs i can't tell you more :-)
And my clubbing is limited to the hotel restaurant in Rakovnik (and an occasional Blues concert at Lucerna Bar in Prague) :-)
WIth my PA28T I have had the last few months "current" problems. I now know that the voltage regulator (12V) very very possible is the culprite. The" best self finder" of the problem I found, is to buy a small meter which you stick in the cigaret lighter which gives directly the full bus power. The meter tells in two digits what the voltage is on the bus and it tells if your voltage regulator gives you what you want** all the time during the flight.** So no workshop figures and advises on the ground. For me minimum 13.5 - 14.00 volt. Further it also quite nicely indicates if there is a charge from the alternator with a small bar which has an arrow if it is unloading. Watch out.. cost $ I4, I payed triple that for immediate shipping through Amazon. Equus 3721 Battery and Charging System Monitor Sold by Amazon.com $14.09
Also as mentioned in this thread,it is very important to keep an eye on the voltage of your battery when on the ground. If it is low...below maybe in the 12 volt range, you still start without problems, so you notice not much but the alternator can not do its work with a low battery, specially if you have a sick voltage regulator, hence no proper battery loading. So just check with a E10 car test equipment the status of your battery off line and additionally with a running engine These automotive testers are quite sophisticated today and do more than advising the voltage.
Diamond with G1000 also has jumping voltage as seen on the MFD… backside of composite aircraft (varying ground potentials).
Lots of busses, lots of consumers, and the strobe doesnt do any good to keep the voltage steady.
/Sam
