Forgot to mark my three wires that attach to doorbell unit

[Reggi]

Hello,

I wonder how to test to see which wire of the three wires goes to transformer screw and which ones go to Front and Back. All the wires are red and then white wires are twisted together. I am replacing the unit and now not sure which wire is which. Thank you

[HayZee518]

chime wires

one wire will be common back to the transformer. the other two will be the front or back door. using an inductive voltage tester is out of the window because it starts to operate at 90 volts and you are working with either 16 or 24 volts.
I don't understand the three whites spliced together and why would [they] bring them to the chime location??
Bout the only reason I can figure out is one of the white wires is hot from the transformer and is spliced into the other two whites going to each push button location.
OK, unsplice all the white wires. briefly touch each white to each red, see which one sparks. the red that sparks is the common lead. connect all the whites back together. now hitch that red to the common and touch each red to the other two terminals and have someone press the back door and front door button to see which door is connected to which chime. if theyt are wrong reverse and permanently connect them. you should be ok now!

[Reggi]

Doorbell

Thank you so much for the information. I have tested my transformer and it seems that it needs to be replaced. Too many large wires going to box so I will be calling an electrician.