I used to have this problem too, until along time ago I read this on 
linuxgazette.com. This should be easier for you, or may be what your looking 
for to fix the problem after this happens. Sory no preventing it as far as I 
know.

The folling is a quote from www.linuxgazette.com Issue 7.
//

Restoring your screen - Kscreen revisited!


 Well, here's a very handy bit of information that I recently came across 
while skimming through one of the Linux newsgroups. 


Remember the 'ol "kscreen" shell function that restored sanity to a screen 
that had gotten all buggered up? Well, here's a very cogent explanation of 
what's happening and how to fix it. The author of this was Henry Wong and 
here's his message: 

>Sometimes, when I inadvertently cat a binary file and get junk on my
>screen, that screen goes into some sort of graphics mode and I can't get
>it out of it.  I've tried changing fonts and SOMETHING changes, stty
>doesn't do anything, capital letters may still appear.  I can switch to
>another virtual console and everything is fine.  When I type commands on
>my messed up (must remember this is going out to the world, use
>euphemisms) terminal it seems to understand.  I can exit for instance,
>or reboot, though what is echoed to the screen is screwed up.

>On sunsite (and mirrors), there's a file called fixvt.sh or something in
>the (I think) system/console directory.  It'll clean this up.

I've done this to myself also.

The console appears to be using some sort of VT100 (or similar)
emulation.  This emulation has two modes: G0 which is usually normal
text and G1 which is usually graphics (these can be changed but is
usually not).  When sending binary text to the screen any ^n (== '\f')
character will switch the emulator to G1 (graphics) mode whereas any ^o
(== '\r') will switch to G0 (normal text) mode.

To force it back you need to have a shell or other program to send the
^o to the stricken display.  I often switch to another virtual terminal
and do an "echo -e '\017' >/dev/tty2" (assuming that tty2 is the
stricken terminal) to restore it back to text mode.

Of course you can put this into a shell program with the tty? as the
parameter.

Hope this helps.

Henry Wong


 So, want to see that this works? Try this: 


In BASH, you can enter literal characters using the vi-type key sequence 
control-v (that's hitting the control key and the letter "v" simultaneously) 
followed by the character you want to insert. So, enter the following at the 
command prompt: 

                ^v^n

 That's a control-v followed by a control-n combination. Hit the ENTER key 
and... 

ShaaaZZzzamm!, instant trashed console! Except now, we know that the terminal 
isn't really "trashed" but merely in graphics mode. All that needs to be done 
is return it to text mode. 


Now, you can "blindly" enter the following: 

        ^v^o

 Hit the ENTER key, and your screen is back to normal. You could also use 
Henry's suggestion for echoing a similar string to the afflicted VT from 
another VT. That is, presuming that tty2 was the afflicted VT, switch to 
another VT and then use Henry's command: 
        echo -e '\017' >/dev/tty2


 Thanks, Henry!! 
\\ The following is a end quote from www.linuxgazetee.com Issue 7

On Sunday 03 November 2002 08:29 am, Entelin wrote:
> When one reads in a binary file to the display it has the chance of
> somehow altering the characters that are used to print normal text so
> its unreadable and scrambled up. Loging that term out doesnt have any
> effect.  How is it that this can be fixed or prevented ?
>
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