The Right Way To Check The Linear Transformer
For a step down linear transformer it is always recommended to use voltage testing method to check if it okay or not. Ring or coil tester may not have the capability to test out the primary winding due to less lesser winding/inductance as compare when you test on the switch mode transformer. Using Ohm meter to check on the primary and secondary winding would not be good enough as it could not detect a shorted winding. The ohmmeter could only check if it open circuit or not.
Since linear transformer can be power “On” so the best is to check the output voltage with your voltmeter. Once you got the right voltage then you can conclude that the transformer is good and if the output voltage/voltages is low or no output then suspect a bad transformer.