"techforce" bravely wrote to "All" (19 Aug 03 15:52:07)
--- on the topic of " Compaq Computer dead -install HD wrong way"

The hd circuit did not get a reverse polarity but rather 12 volts on the
5 volt logic circuit supply. Think about it, the plug is symetrical.
Ordinarily the supply filter caps "if large" should have absorbed the
overload and held down the 12 volts.

If the overload was brief then perhaps a prolonged rest to allow
junctions to discharge internally may be all that's needed to restore
operation. I've seen this "let rest then it works" behaviour before.

OTOH if power was applied for a long time then some logic IC or line
driver got very hot and turned to toasty carbon letting the smoke out.

Reversed power plug happened to me once with a wd drive. The line driver
IC was visibly puffy, cracked, and fried. Took one from a defunct wd and
the drive worked perfectly! In hindsight I guess it bravely sacrified
itself to save the mctlr... snif!


te From: "techforce"

te If you reversed the IDE cable, the PC would not power up more than
te likely , until you corrected the problem. Some older PC's would power
te Up, but would not see the drive.

te As for the Reversed Polarity, more than likely one of the SMD Chips
te Fried when it was applied. I have seen other items designed with a
te Diode accross the Power pins to soak up the power. But I guess the
te amount of current it drew was still within the safe limits of the
te output of the main PS, otherwise the PS would have tripped off and
te saved the drive.

te "Wdyorchid" wrote in message
te ...
I'm talking about the four wires with trapezoid lead. The tab that broke
te off is
on the hard drive. Correct me; the tab is nothing but the base of the
trapezoid. Assuming a trapezoid without a base would eventually allow the
lead
to go in any direction. The male prong inside the trapezoid on the hard
te drive
is flexible and will bend slightly to become devilish.

After putting it back to it's correct power voltage (before it had been
12V
into 5V and 5V into 12V) I'd notice the hard drive acted strange as the
data
pickup arm jerk back and forth like a tail of a fish out of water. I'm
te still
wondering what would happen if I had instead reverse the ribbon cable
te instead
of the power cable.
-Wd

Are you talking the IDE ribbon cable, or the four wire power lead? The
four
wire power lead is trapezoid shaped and doesn't have a "tab" to break
off.
It would take a LOT of forcing to get it to fit reversed. But the IDE
ribbon cable does have a simple "tab" to "key" it so it fits only one
way.

-Steve


Wdyorchid wrote in message
...
My computer stops loading the operating system and will not boot
te because
I'd
decided to install my hard drive's power supply in reverse polarity.
The
hard
drive is fried. But I'd like to find an alternative way to boot my
computer
with a fresh hard drive. You're wondering how in the world can I
te reverse
polarity on my Maxtor 20G. Easy, the tab that's supposed to prevent
reverse
polarity broke off. Fumbling in the dark, it's an accident waiting to
happen.
Price of Computer $1,200 Compaq Presario 2256. HD Maxtor $100. Monitor
not
included. I'd assume people don't diagnose motherboards, do they just
replace
the board? What's an alternative way to boot unless it can be fixed?
-Wd


.... The current limits placed are based on resistance