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PCBUILD - Personal Computer Hardware discussion List <[log in to unmask]>
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Sat, 10 Sep 2005 01:42:09 -0700
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For David and the other list members regarding the light staying  on Diane's
floppy.
I have been following this thread for several days but  usually don't have
time to respond and other members can usually supply the correct solution.
I have been an Elect Tech for over 40 yrs and repairing computers since 1982
and have seen many instances of floppy light staying on.
I agree 100% with the diagnosis that this is usually caused by the 34 pin
cable being plugged in upside down and reversing it will usually correct the
problem. If you were to look at the schematic of this drive you will see
that plugging the cable in wrong will not damage the drive or motherboard.
This cable only carries data signals, 0's and 1's. 0 is considered 2 volts
or less, 1 is considered 3 to 5 volts. A0 is generated by grounding , ie-
pulling the 5 volt line to ground. The transistor providing the 5 volts is
prevented from being damaged by the use of a pull up resistor that prevents
too much current from flowing and burning out the transistor. The 34 pin
cable has 2 rows of pins. One row is the even numbered pins, 2 thru 34 and
carries the data (0's&1's). The other row is the odd numbered pins, 1 thru
33. These pins are all grounded. Therefore if you plug the cable in upside
down all you do is pull all the data signals to ground which they are
designed to do. This will not damage anything. Techs troubleshoot these type
circuits by shorting Hi's to grd to make them 0's and forcing 0's Hi by
injecting a 5 volt signal.Turning the cable over will allow  the floppy
interface to properly commnicate with the motherboard  and tell the mobo the
floppy is there and ready to proceed. During post the bios sends a signal to
the floppy to check to see if it is there and what is it's status. This
causes the light on the floppy to blink momentarily. If the light stays on
all the time it means it wasn't acknowledged by the bios therefore it will
not read a disk because it doesn't know the drive is there.
If the cable is turned over and the light stays on, you have other problems,
poss bad floppy or some component on the mobo.
If anyone would like to confirm my comments I suggest you get a copy of
"Bigelows Troubleshooting, Maintaining & Repairing PC"s, 5th Edition, Pg's
700 to 711.

The win ME boot disk does not include the command files, therefore you
should always use a Win 98se boot disk.

In the bios, "Floppy Drive Seek" must be enabled or the floppy drive will
not be acknowledged during boot.

Sorry for the lengthy post but hopefully it will help everyone better
understand how computer circuits work.

Good Luck to All,
John Dinges

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