My scanner attacked my PC!

[Rob Worsnop]

Yesterday my scanner launched an unprovoked attack on my relatively
new PC. The scanner, an obsolete model anyway, had to be put down. The
PC I would like to nurse back to good health, and I would appreciate
help.

The scanner used a parallel port, as does my trusty 1993 Epson
ActionLaser. As I was swapping the cables, the scanner launched its
vicious attack. Sparks were flying between the pins on the scanner
cable and the parallel port on my motherboard.

It seemed that the scanner had cleverly found a way of channelling its
15V power along the parallel cable!

My PC responded to this unexpected current delivered to its innards by
freezing up. It rebooted OK, but now seems rather unstable. Since the
attack, Windows 2000 has frozen several times, always requiring a
power-off shutdown.

This may seem like a rather "out there" question, but does anyone know
offhand what would be the likely effect of sending 15V DC into a
motherboard's parallel port? I am trying to work out what, if
anything, I need to replace.

If it helps at all, my PC is built around an ASUS P4P800 Deluxe
motherboard and my graphics card is of the AGP type.

 

[Noozer]

The scanner used a parallel port, as does my trusty 1993 Epson

ActionLaser. As I was swapping the cables, the scanner launched its
vicious attack. Sparks were flying between the pins on the scanner
cable and the parallel port on my motherboard.

You DID have the PC and Scanner turned off while swapping the cables, right?

It seemed that the scanner had cleverly found a way of channelling its
15V power along the parallel cable!

Doubtful, since the power should be off while swapping. Otherwise damage to
the scanner or parallel port may occur.

My PC responded to this unexpected current delivered to its innards by
freezing up. It rebooted OK, but now seems rather unstable. Since the
attack, Windows 2000 has frozen several times, always requiring a
power-off shutdown.

Hope the PC is under warranty... Backup your data and try running a scandisk
to see if the files are damaged. If not you may need to send the PC back for
replacement - don't mention the scanner at all.

 

[DaveW]

Well, in theory, some chips on your motherboard are now toast.

 

[Michael Culley]

Yesterday my scanner launched an unprovoked attack on my relatively
new PC. The scanner, an obsolete model anyway, had to be put down. The
PC I would like to nurse back to good health, and I would appreciate
help.

The actual earth voltage on 2 different devices can vary. So the voltage at
the parallel port might be 15V but the earth could be 30V different from
your PC so the voltage on the pins according to your computer is 45 volts!
When you plug the printer into your computer the voltage difference is
eliminated but there is a sudden rush of current. To get around this you
should, as others have said, plug your scanner in when the PC is off, or
touch the earth of the plug on the case to remove the voltage difference.
This is possibly only true for devices with 2 pin power plugs.

To fix your PC first try reinstalling windows (not over the top). If that
doesn't work you should start replacing parts until the problem goes away,
most likely the motherboard is the problem. Ironincally the scanner is
probably still ok.

 

[Rob Worsnop]

You DID have the PC and Scanner turned off while swapping the cables, right?

I'm afraid not! I don't know if it's the modern USB/firewire devices
lulling me into a false sense of security, or just 15 years of bad
habits, but I was hot swapping.

Doubtful, since the power should be off while swapping. Otherwise damage to
the scanner or parallel port may occur.

See above. Actually it's probably a good job I was bending the rules
vis-a-vis hot swapping. If I had powered everything down before
swapping cables I wouldn't have seen the sparks and I would probably
have allowed 15V DC to flow through my parallel port all day.
Incidentally, I saw no sparks when repeating the "experiment" with my
scanner unplugged from the mains.

Hope the PC is under warranty... Backup your data and try running a scandisk
to see if the files are damaged. If not you may need to send the PC back for
replacement - don't mention the scanner at all.

I don't think the problem is with the hard disk. At one point even the
motherboard logo was all distorted on startup. Just to be on the safe
side I will run scandisk anyway, though.
I built the PC myself, so sending it back is not really an option.

Thanks for your help. Any idea what the damage might be?

 

[Michael Culley]

See above. Actually it's probably a good job I was bending the rules
vis-a-vis hot swapping. If I had powered everything down before
swapping cables I wouldn't have seen the sparks and I would probably
have allowed 15V DC to flow through my parallel port all day.
Incidentally, I saw no sparks when repeating the "experiment" with my
scanner unplugged from the mains.

Did you read my reply?

 

[Rob Worsnop]

Did you read my reply?

Have now, thanks. I was reading this newsgroup using Google Groups. I
posted before your reply had appeared there.

 

[Rob Worsnop]

The actual earth voltage on 2 different devices can vary. So the voltage at
the parallel port might be 15V but the earth could be 30V different from
your PC so the voltage on the pins according to your computer is 45 volts!
When you plug the printer into your computer the voltage difference is
eliminated but there is a sudden rush of current.

It didn't seem to eliminate the voltage difference. I had it plugged
into the parallel port for several seconds and it would still spark as
I unplugged it. Would this suggest another cause?

To get around this you
should, as others have said, plug your scanner in when the PC is off, or
touch the earth of the plug on the case to remove the voltage difference.
This is possibly only true for devices with 2 pin power plugs.

To fix your PC first try reinstalling windows (not over the top). If that
doesn't work you should start replacing parts until the problem goes away,
most likely the motherboard is the problem.

It's not been misbehaving over the last day. But the "cheapest-first"
approach makes sense and I'll do this if necessary.

Ironincally the scanner is
probably still ok.

I don't think the old Mustek survived the drop into my trash can.
Actually I've been looking for an excuse to replace it for years:
apart from having a parallel port, it was 1200 X 600 dpi and couldn't
scan negatives. Maybe I should have sold it in a garage sale. The $3
would have offset the cost of the Canoscan 4200F that's now on its way
to me.

Thanks for the advice.

 

[Michael Culley]

It didn't seem to eliminate the voltage difference. I had it plugged
into the parallel port for several seconds and it would still spark as
I unplugged it. Would this suggest another cause?

Quite possibly. My scanner sparks if I touch the plug on the case but I'm
not sure if it does when I remove it. I'm not game to try now!

Michael Culley

 

[Alceryes]

Turn the parallel port off in Bios and use USB...
P.S. I've been running a computer business for 3 years now and ALWAYS hot
plug parallel ports (not swap from one to another but definitely plug in).

I'll think twice next time...