debugging a tu58? blank tapes or bad read channel?

Does anyone have any suggestions about debugging a TU58? This is a dual TU58 from a vax 730. The symptom is that when I try to boot from it the tape rewinds a bunch of times and then reads off the end of the tape. I removed it and poked all around with a scope and the schematics. The motor control is fine as well as the tachometer. The read channel shows no activity, even when I put a tape in and move the tape. The micro seems happy. I connected it to "tu58ctl" and I can talk to it and send/receive commands. But when I try to position the tape I get a "motor stopped" error. I'm begining to wonder if the 3 TU58 carts I have have been bulk erased. I have no "known goods" and I've never read these tapes. I made the assumption they were good but that might be a mistake. (wish I had those mythical proms which can write carts :-) I put a scope on the signal from the read heads and I see nothing when the tape spins by. I find that very odd. I would think I'd see pulses even if the blocks where all zeros... So nothing makes me think the tapes have been bulk erased. Is there any way I can test the read channel without having a good tape? (I assume not, but I know very little about tape drives, perhaps there is some 'technique'). I know the tapes are useless if they have be bulk erased - but will the symptom be no read channel activity? (I assume so). blah. if I've wasted all this time on bulk erased tapes %$#%@#@!#$ -brad