How to test this transformer

With just a circuit board containing these connections lighting a dim bulb tester hard on I need to test just the main transformer, to separate this would I connect 230v live to AC5 and neutral to AC3?
Screenshot_20220729-171937_Adobe Acrobat.jpg
Which transformer?

You only show half, which is same as nothing.

Please post more complete schematic.

No guessing allowed on mains circuits.


1) what´s wrong with connecting mains the proper way, straight at "K001 - Power In"?

2) I hope you are not inserting both jumpers J001 - J002 at the same time,it´s either one or the other

3) disconnect all secondaries (half) shown: at K25 and incomplete/not shown connectors under it

Much suspect your shining lightbulb comes from a secondary load problem, rather than transformer itself or its primary connections.

Even if not, let´s separate them for confirmation.
Secondaries resistance measurement

Across k25 0.64r continuity across

Across k23 3.45r continuity across

Across k22 0.52r continuity across

Across k24 pins 1-3 4.78r continuity
3-2 2.49r continuity
1-2 2.49r continuity

Primary resistance measurement

Across k21 pins AC 3-5 9.68r continuity
5-4 2.25r continuity
4-3 7.62r continuity