Need some help with identifying the primary on a power transformer
Figure 1. Close-up of the transformer connections.

Following the traces on the left out to the edge of the board we find the 120 - 240 switch legend so the left side is definitely the mains input or primary.


If the internal non-replaceable fuse is intact you should get a zero ohm reading between 5 and 6.
Read the resistance between 3 to 6 (120 V winding) and 2 to 6 (240 V winding) and you should find that the first reading is half that of the second.
Finally check that 1, 4 and 7 have no connections to other terminals.


It may be that the internal fuse has failed on thermal protection. You could power the transformer on 8 but that would not be recommended.

If there's a chance that the transformer has an internal short you can safely power it up with a mains light bulb in series with the primary. The bulb should not light - or very dimly at best / worst - if the transformer is OK.

Finally, note that the board uses very many standard length wire jumpers as bridges over the traces. In many cases several jumpers could have been replaced with one long one or better layout. It appears that the board was designed for pick and place population with standard "zero ohm resistors" (pre-formed wire links).