Need help with Moog Source power regulated sound changed

Hello everybody
I’m a new proud owner of a Moog Source I had shipped from someone in Japan.
I used a step converter to make it fit the right voltage, The synth sounded very clean and nice specialty after I calibrated the tuning pots it is stable quite good tuning actually.
The label in the back says
120v/60hz
100v/50hz
30watts

So recently I decided to get the synth power supply modded to my countries voltage which is
220v/50hz

The Tech did it very quick after looking in the service manual. He joined a couple of wires and it turned on with no visible problem.

I came home and played the synth but now it sounds a little deferent.. The tuning is fine and stable
but The sound is not as clean as it sounded before, it’s similar but with some extra side effect..
I would describe it as a little dirty and fuzzy undernith, with some very low background kind of ring modulation effect. It’s Like some lfo action going on in the background but with a light effect on sound
Very hard to describe but call me crazy it’s not the same as it was when I used the step converter pre modding..
I tweeked the sound to calibration test mode ( saw tooth with nothing on it) and checked all the buttons.. Then I noticed when pressing any button on the synths panel there is this very low little noise of static electricity..
Does anybody have an idea what went wrong and what can I do about it?
I am worried something is wrong and want my synth to sound clean as before
I would like to try checking it DIY as it’s complicated for me to reach the tech..
I will apretiate any suggestion

Thanks

OL.

You have a fault that’s has appeared… probably something disturbed whilst it was opened up…?
Just rewiring the mains transformer to a different primary winding configuration wouldn’t have any effect on the sound…!
You should take it back to the tech…

Cheers,
Tom

Hi Tom
Thanks for your advice,
The sound change is barley noticeable, I would think most people wouldn’t hear it but I do hear something deferent.. Maybe the electricity in my room is unstable , might have unstable current..
I assume the tech will tell me he can’t find enything wrong..
How can I test to see if the moog is working correctly?
What is the test procedure and what tools do I need?

Thanks
OL