Michael J. Mahon wrote:
RedskullDC wrote:Hi Schmitd,"schmidtd" <schmidtd@my-deja.com> wrote in message 1177263826.143384.84240@d57g2000hsg.googlegroups.com">news:1177263826.143384.84240@d57g2000hsg.googlegroups.com...I picked up a rev 4 B&H machine the other day. Integer ROMs, raised power key, dark green slots, serial 27xxx something with 7930 date. It's temperamental as those machines tend to be - and I have some keyswitch rebuilding to do as well. One problem is truly vexing me: it trashes track zero of any disk I feed it when booting. I have tried different power supplies, different disk controllers, different ROMs (I plugged in a set of Applesoft ROMs on a switchable card), and even swapped out every chip from a known-good mobo. Still I get the same behavior: booting with the disk card in slot 6 causes disks to lose their minds. They become unbootable, uncatalogable, and have to be reformatted (not just re-imaged) in order to be reused. What on earth might be causing this?Process of elimination: 1. Try a different drive.If this fixes the problem, I would be inclined to look around Q2 or the ULN2003chip on the drive board.If the 2003 chip has failed, it may be turning the Erase head on when it shouldn't.= Random trashing of the diskette, but no permanent physical damage.The 74LS125 is even more likely to cause this problem, since it is directly connected to the cable, and vulnerable to ESD and misplugging.
(Of course, so is the ULN2003, but in my experience the '125 out-fails it by a good margin.) -michael NadaNet networking for Apple II computers! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it's seriously underused."