Most parts state that for direct sunlight to erase EPROMs, you're talking
*days* of continued exposure. The energy of a UV erasing bulb is *much*
higher than the tube in a scanner. And obviously a scanner tube contains a
low amount of UV, or it would sport a required warning for eye damage.
--John
-----Original Message-----
From: cctalk-admin_at_classiccmp.org [mailto:cctalk-admin_at_classiccmp.org]On
Behalf Of Don Maslin
Sent: Thursday, May 16, 2002 20:50
To: 'cctalk_at_classiccmp.org'
Subject: RE: [CCTALK] EPROM Life... Was: scanners & circuit boards...
On Thu, 16 May 2002, Corda Albert J DLVA wrote:
> Now, I don't know the construction/nature of the tubes used
> in scanners, but I myself would be wary of photocopying or
> scanning a PC board with an unprotected (i.e. uncovered) EPROM
> window face-down on the scanning surface. My reasoning is
> as follows;
>
> Although a fluorescent tube in good condition shouldn't emit
> much UV, one has to remember the way such a bulb functions.
> The excited gas inside the tube emits almost entirely in the
> UV spectrum. This is converted to the visible spectrum by the
> phospor coating on the inside surface of the tube. Over time,
> I have seen some of the coating flake off the inside of old
> flourescent tubes, providing a bunch of small UV "windows".
>
> Most UV Eproms begin to erase when exposed to UV wavelengths
> shorter than 4000 A (Angstroms). I found the following
> statement concerning EPROM sensitivity to UV light on page
> 10-9 of the National Semiconductor 1984 "CMOS Databook" (and
> yes, I _am_ a packrat when it comes to old databooks :-)
> concerning the 27C16 (a very common older type of EPROM):
No one that I have know of has taken note of the brevity of
exposure to the light of a scanner or a copying machine. It
seems to me that barring many repetitive exposures - and I
mean MANY - the likelihood of damage is almost nil. And, of
course, there is also the UV blocking of glass as well.
Chicken Little, anyone?
- don
> Erasure Characteristics:
> "... It should be noted that sunlight and certain types of
> fluorescent lamps have wavelengths in the 3000 A - 4000 A
> range. Data shows that constant exposure to room-level
> flourescent lighting could erase the typical NMC27C16 in
> approximately 3 Years, while it would take approximately
> 1 week to cause erasure when exposed to direct sunlight..."
>
> Also, one must keep in mind that the timeframes listed
> above are probably derived from studies of "freshly programmed"
> eproms. Most of the ones we would be interested in would
> already have a number of years of charge decay under their
> belts. I was unable to find a reference to a finite lifetime
> for UV Eproms, but I seem to vaguely recall that there is
> a limit (~10 Years? sounds short, but I seem to remember
> reading it somewhere. Does anyone have this number at hand?)
>
> The end result of all this is that if you have any equipment
> you consider valuable, and it has windowed EPROMS, make certain
> that the windows are covered with an opague sticker. You might
> also consider dumping their contents to a data file for archival
> purposes. (and possibly re-programming them to effectively
> "refresh" them).
>
> -al-
> -acorda_at_1bigred.com
>
>
> > -----Original Message-----
> > From: Tothwolf [mailto:tothwolf_at_concentric.net]
> > Sent: Wednesday, May 15, 2002 4:16 PM
> > To: cctalk_at_classiccmp.org
> > Subject: Re: [CCTALK] [CCTECH] scanners & circuit boards...
> >
> >
> > On Wed, 15 May 2002, Jeff Hellige wrote:
> >
> > > What's everyone's thoughts on placing circuit boards directly on the
> > > bed of a scanner for imaging? Any possibility of damage to
> > the board
> > > from the light or other parts of the scanner? I've done it before
> > > with good results but not with anything truly unique.
> >
> > I'd be more concerned with accidentally scratching the glass
> > bed of the
> > scanner due to sharp component leads. I guess that there is a slight
> > possibility of degrading the contents of an EPROM if its window isn't
> > covered. The fluorescent tube the scanner uses to illuminate the bed
> > really shouldn't be emitting too much in the way of UV or
> > near UV light
> > though. Other than UV erasable components that don't have their window
> > covered, I can't think of anything else I'd be concerned about.
> >
> > -Toth
> >
> > _______________________________________________
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> > http://www.classiccmp.org/mailman/listinfo/cctalk
> >
>
>
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Received on Thu May 16 2002 - 20:04:24 BST