Don't know what you mean by "it's blind". Presumably you mean that it has a built in encoder? Otherwise it couldn't report its height / Mode C...
It would have helped if you said what sort of transponder it is (and used capital letters and punctuation
).
If its a built in encoder, it will have a static port / connection (which should be the same static source that your altimeter is using). Check that is OK. Otherwise, its a trip to the avionics shop for diagnosis / repair.