a bit frustrated with avionics upgrade

[beechcraft flyer]

Good day pilots. i upgraded my avionics to a gtn 750 and two g5's from having no gps and just the standard six pack. it has been a struggle to get the stec 60-2 to cooperate with the g5 hsi/heading bug. first was a resistor change and a new turn coordinator , stec 60-2's apparently use the turn coordinator for the roll function. Upon test flight all went well and then the stec head unit was sent of for tune up including burnt out bulbs and being stuck in soft mode and new buttons , and when flown again it would bank hard left when nav selected. The roll computer is now being bench checked for voltage issues at stec. Is this a common issue when adding upgrades etc to a non garmin auto pilot ? been a frustrating 10 weeks and i want to fly. Thanks in advance my plane is a 1966 debonair

 

[MooneyDriver78]

I had similar problems with stec 50, the G5 emulates a certain type of HSI which I can’t remember now, but that’s why the resistor change. Then it needed to be sent back for repairs, it worked ok afterwards.
Old avionics are fragile I guess, I also had a master switch break. Another time I found the shop attaching a 24v power supply to my 14v airplane so I wonder how many times these are shop induced failures?