FM works, AM nada. What's the problem?

I bought a 96 SR5 in January and the power antenna is frozen in up position (not sure that has anything to do with this issue though). FM radio is fine, but when I switch to AM I get nothing across the dial. I do see the frequency numbers and if I manually increment the frequencies, can see the little 2, 3, etc of the button settings. I've also tried setting it to known-strong stations in this area with volume all the way up. I hear hiss, but no voice. Not even a faint one among the hiss. Any ideas?

I would be easy to pull the radio out and hook up another antenna to it to test with...

I would venture to say you could git another stock head unit fer cheap...

Heck...I would even put one of the Scion units in there. T1806 or T1807 would work just fine as those would give you MP3 capability. Or if you still need tape/CD capability, you can put in the double DIN units from the other Toyota cars...like the Gen 4 Camry... :D