Cool! Yes, the transformer provides isolation from the line. Draw a little ground symbol on the long line at the bottom and that can be your reference for logic ground.
PS.
If the transformer puts out 40 volts RMS X 2 windings that will give ~ 112 volts when you filter it. A lot of "stuff" won't like that.

Great thanks that's awesome news for debugging that then I still haven't changed that transformer symbol sorry, it's not a centre tap for the 2x40v in series (even though that's what it shows lol ) but dual secondary's in parallel for more current.

 

Back in the 1970's we would float the scopes on the line for occasional tests, but that was in a lab with other people around who knew and understood the danger and could perform cadio-pulminary respiration (CPR), and standing on a rubber floor mat. These days I think it would be a pretty dumb thing to do since good isolation transformers are available that would allow one to ground the scope and many points in an AC operated circuit under test.

If you are going to be doing work on off-line power supplies or line powered circuits invest in a really good isolation transformer -one with very low leakage current and capacitance between the windings. It could easily save your life -what would that be worth to you and your family?

Thanks Yeah I won't float the scope, knowing my track record I would probably do it on a metal bench and bare footed or some equally silly thing . have been looking at the option of an isolation transformer but they are just so dam expensive

 

There is a good Youtube video on this subject titled appropriately "How Not to Blow Up Your Oscilloscope". It is worth watching and he explains in easy terms what is going on. Good luck, play safe.

Aye! That ("Bill Nye Wannabe"?) EEVblog presenter is more than I can stand! - Can we say pressure of speech!? --- For all that, he is a good resource for beginners though - if one can bear to attend his ravings!

Best regards
HP

Yeah! Granted! -- Nobody, but nobody, is as annoying as Bill Nye!

 

.............Yeah! Granted! -- Nobody, but nobody, is as annoying as Bill Nye!

Mr. Bean??

 

Mr. Bean??

Touché