What you need to do is isolate the loads that are on the transformer and put a amp meter on the transformer and read the amps while you put the loads on one at a time. the one that spikes is the one thats bad. You can put a inline fuse in to protect the transformer. A 3 AMP fusw qould be good for a 75 va transformer if its a 50 va you would need a 2 ampo fuse.
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What you need to do is isolate the loads that are on the transformer and put a amp meter on the transformer and read the amps while you put the loads on one at a time. the one that spikes is the one thats bad. You can put a inline fuse in to protect the transformer. A 3 AMP fusw qould be good for a 75 va transformer if its a 50 va you would need a 2 ampo fuse.