SOT: Scanning old computer docs

[Jon Elson]

On 04/02/2021 07:56 PM, Kevin Parker via cctalk wrote:
> If there is anyone on the list familiar with scanners I'd be most grateful
> for some advice please.
>
> Some time ago I bought a HP 8270 sheet feed (full duplex) scanner NOS. I
> wanted to digitise a whole heap of old computer documentation and for a
> little while I've been working through the big heap of stuff. But for quite
> some time I've had an issue with scans that go through the sheet feeder
> (irrespective of whether I do them double sided or not). Basically the
> problem is that anything that goes via the sheet feeder has issues with
> "streaks" in the document whereas anything done on the flat bed is perfect
> (I have some links to some examples below).
>
> By way of clarity, anything done on the flatbed the lamp traverses the flat
> bed to do the scan. For sheet fed items the lamp is moved to specific slot
> on the scanner and the sheet feeder takes over wrapping the document past
> the lamp. Given that flat bed scans are OK I don't think its an issue with
> the lamp.
>
> I've done the following things to try to resolve the issue with no joy:
>
> * Checked for any specific settings
> * Tried doing scans in grayscale
> * Tried increasing the resolution (default is 300dpi) to slow the speed that
> the document is fed through the feeder.
>
> According to HP the issue is a cleanliness one i.e. dirt on the glass can
> cause reflections. I've followed their instructions for cleaning the glass
> but still no joy.
>
> Flatbed  example.
>
> https://drive.google.com/file/d/1jYiFzERiZiaq7-WoTiQ2eIzITn6giviR/view?usp=s
> haring
>
> Sheet feed example.
>
> https://drive.google.com/file/d/1WF4SHbwV3bVET_bzwIUiULywbCGZBf_V/view?usp=s
> haring
>
>
When in flatbed mode, there is probably a foam mat that 
presses the document firmly onto the glass plate, even if 
the page has a warp or curl to it.  To prevent jamming, the 
sheet feeder probably leaves the page loose, and if warped 
or stiff, it won't press flat to the glass.  There may be 
something you can adjust to get the page to be closer to the 
glass, but not so tight that it prevents the page from 
moving.  That might be a delicate balance.  But, I can sure 
see how a page that is several mm away from the glass could 
get reflections that wash out the details.
There may be a damaged stop somewhere that sets the 
clearance between whatever conveys the page and the glass, 
or maybe even a missing belt or pad that holds the page 
close to the glass.

The difference is QUITE obvious, almost making the sheet-fed 
scan worthless.

Jon