PC Hardware in a Nutshell, 3rd Edition

Locating pin 1

If you upgrade your system and it fails to boot or the new device doesn’t work, chances are you connected a ribbon cable backward. This can’t happen if all connectors and cables are keyed, but nearly all systems have at least some unkeyed connectors. The good news is that connecting ribbon cables backwards almost never damages anything. We’re tempted to say “never” without qualification, but there’s a first time for everything. If this happens to you, go back and verify the connections for each cable. Better yet, verify them before you restart the system.

Warning

One of the experienced PC technicians who reviewed the first edition of this book tells us that he has “burned up” more than one floppy disk drive by installing the cable with the pins offset. We have frequently installed FDD cables reversed, offset, and in any other combination you can imagine (it always seems easier to seat a cable by feel than it does to remove the drive and do it right) with no worse result than the system failing to boot. The FDD cable carries only signal-level voltages, so we’re not sure how offsetting pins could damage a drive, but we’ll certainly be more careful in the future.

To avoid connecting a ribbon cable backward, locate pin 1 on each device and then make sure that pin 1 on one device connects to pin 1 on the other. This is sometimes easier said than done. Nearly all ribbon cables use a colored stripe to indicate pin 1, so there’s little chance of confusion there. However, ...