Beware of the CMOS and loose cables when fixing a floppy drive

When troubleshooting a floppy drive, the disk is the first place to look for the cause of the problem. Once you've ruled the disk out, however, it's time to focus on two potential culprits of drive problems: loose cables and incorrect CMOS settings.

The first step in troubleshooting a malfunctioning floppy drive is to determine whether the disk or the drive is the root of the problem. Once you’ve ruled out the disk, you’ll need to move on to phase two of your troubleshooting effort: looking for the symptoms that will tell you what is wrong with the drive. In this article, I’ll discuss what symptoms point to a problem with loose cables, as well as when to direct your attention to the CMOS settings.

A Q&A session
During this next troubleshooting effort, you’ll need to ask a series of questions, including:
  • When you attempt to access a disk in the drive, does the drive’s light come on?
  • If the drive light does come on, does it go back out?
  • Can you hear the disk spinning?
  • Can you hear the drive heads moving?

Each answer can provide a clue to the drive’s problem. For example, if your drive light stays illuminated constantly, then the drive is definitely getting power. (Note: A continually lit drive light usually signals a reversed connection to the floppy disk controller.)

On the other hand, suppose that you attempt to access a disk in your drive and the drive light never illuminates. This could be because your request is never reaching the drive in the first place or the drive may not be getting any power. Your next step, then, is to check the cables.

Placing the blame
Check out my article "Start with the usual suspects when diagnosing floppy-disk problems," in which I outline steps for determining whether a 3.5-inch floppy drive problem is related to a disk or the drive itself.

Check for loose cables
There are two cables that should be attached to the floppy drive: the power cable and the data cable. You can see an example of these cables in Figure A.

Figure A
A data cable and a power cable attach to each floppy drive.

Although it’s uncommon in this day and age, you can daisy chain two floppy drives together. The computer in Figure A is using such a configuration. The reason why I mention such an uncommon configuration is that, as you can see in Figure A, the two floppy drives are sharing a common data cable. If the cable works its way partially loose from either drive, the remaining drive can sometimes also be affected. Therefore, if you have an older system with two floppy drives, and your primary drive starts to fail, it could potentially be the result of a loose cable on a drive that you never even use.

Once you’ve verified that the data and power cables are securely attached to your floppy drive, you should verify that the data cable is also attached securely to the floppy disk controller. The data cable has a red stripe at one end. This stripe corresponds to pin 1 on the controller. Usually, pin 1 is designated in some way. You should also verify that all of the pins on your floppy disk controller are straight and that the data cable is connected to all pins. It’s easy to accidentally connect the data cable in such a way that some of the pins fall outside of the connector.

At this point, you should power up your computer and try to access the floppy drive. Again, look for all of the symptoms that I described earlier. If you still can’t access the drive, then the next step is to check your computer’s CMOS configuration.

Don't forget the CMOS
Although the method of accessing a system’s CMOS setup is different for different systems, it usually involves pressing the [Delete] key or [F1] key at some point during the early stages of the boot process.

The computer’s CMOS tells the system what type of hardware is installed. On older systems, if the CMOS battery goes dead, the CMOS settings will revert to their default values, which may sometimes incorrectly identify the floppy drive. For example, the system may think that your drive is a 5.25-inch drive instead of a 3.5-inch drive. There are also viruses that are designed to modify the CMOS settings and tell your computer that a floppy drive isn’t installed. At any rate, just make sure that the CMOS correctly identifies your drive type.

Editor's Picks