Atari 1050 diskette drive repair

Tony Duell ard at p850ug1.demon.co.uk
Wed May 28 15:15:33 CDT 2008


> 
> On Tue, 27 May 2008, Tony Duell wrote:
> 
> >>
> >> Anyone have experience with these?  I have a defective unit (purchased on
> >> eBay - sad story) that tries to bash the drive head to death against the
> >> Track 0 stop when turned on.  I picked up the service manual and
> >> schematics and was able to verify that the Track 0 sensor was working and
> >> that that NTRACK00 (pin 34) on the 2793 FDC chip is pulled high at that
> >> point.
> >
> > I don;t have the data sheet in front of me (and I certainly don't haev
> > the 1050 schematics here), but if that signal name 'NTRACK00' means the
> > obvious thing, it's _not_ Track0. In other words it should be low when
> > the head is on track0.
> 
> That threw me as well.  There must be a misprint somewhere, since the unit 
> works just fine when I substitute a known-good 2793 from another drive.

I have checked the WD279X data sheet, and that pin is certainly 
active-low. It's shown with a bar over it on the pinout diagram and in 
the table of signals, it's also descried (under the 'Restore' command) 
as being asserted when low.

Now, I suppose it's possible that your defective 2793 had a short from 
this pin to Vcc, so that the track0 senosr circuit couldn't pull it low. 
That would make it test high all the time. But if it's low normally, goes 
high when the head is on track 0, and yet a new 2793 fixes the problem, I 
don't know what the heck is going on. 

-tony



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