Qume Qumetrack 542 track seeking issue

Been away for some time from the mailing lists.... getting back into my classic gear again.... I have two of these Qumetrack 542 drives. While testing my 360K drive collection (8 drives.... I must be slacking :-) ...), 2 worked, 4 had issue (resolved with a good head cleaning), and 2 (both of the Qumetrack 542 drives (I have two of them)) have mixed results. My testing is on a Tandy 2500SX/33 using the Tandy straight through cable and with the drives set do DS0. I seem to have no issue with Dunfield's testfdc (using testfdc/x a:) with these drives, doing SS and DD and getting 'pass' from testfdc. However, when I do a format a:, the drive will format through the 40 tracks, then instead of the heads returning to track 0 quickly, they do these small stepping 'bursts' and DOS times out saying failure..... it probably would have worked if DOS would wait 10 seconds or more for the drive to move to track 0. I've never seen behavior like this. I even tried an external power supply in case the Tandy one wasn't up to driving the full height floppy drive due to an aging marginal supply, but that didn't help anything. I've now also had one of them shut down the power supply (a shorted tantalum cap I'm sure). I've looked through the manual on the drive, I've tried the HM, HS, and no jumper setting for stepper motor power, same results in all cases. I'm trying too determine if these drives are good. I'm planning on using them in a Tandy Model III that is upgraded internally to a Model IV, but I feel these are basic drives and should work in DOS fine too. I hope someone has a clue, as I'm tapped out of them currently. Thanks, -- Curt