I have a Shugart 800-8 with a media centering problem. I know it is definitely that and not something else (say, electronics, TRK00 position, etc.), because I can see the "wobble" in the signal coming from the heads on a 'scope. Depending on how I load the floppy, the attenuation can be from nothing (in which case the floppy reads/writes fine, including exchange with other drives - the Altos has a nice floppy diagnostic), to as much as 80% (in which case I cannot boot from it, it won't read anything at all). So, it isn't the TRK00 position or anything like that.
With a 'scope, I can see that the wobble is a bit over 80ms in period - 1/2 the rotation time, confirming that it is wobble. It isn't slipping or anything like that, and I have tried different media as well, to make sure that the issue isn't a worn hole in the floppy, etc. I can usually get it to center properly if the drive is on its side, and when I close the door I close it slowly, and "massage" the door (a bit more closed, a bit more open a couple of times) just as the clamp starts to engage the spindle - say, two out of three insertions work fine. This also confirms that the spindle itself is not wobbling, aside from simple In the normal position of this system, the drive is upside down, with the motor-driven spindle on top. In that position, I am lucky to get it to work one out of five times. The issue is not the head load tension or pad, either -- even when off center, the peak amplitude is just fine, and when properly centered, the amplitude is the same as the other drive on this system on tracks 0, 38 and 76. I have exchanged the spindle clamp with another drive, and also the eject mechanism (the spring was a bit stretched when I first got the drive, but I repaired that) as well, to no avail. The handle was a little out of adjustment - coming down a bit too close to the spindle (but not interfering with it), but adjusting that did not seem to help either. When I look at the cartridge guide without the spindle clamp in place, it is now centered above the spindle, and at the same distance from the spindle as my drive that does not have these issues. Anybody have any experience like this? Thoughts? There really isn't much to adjust on these things. JRJ