[sane-devel] Medion MD9850: scan range & noise probs?

Wolfgang Fabics wolfgang.fabics@chello.at
Thu, 30 Oct 2003 19:03:10 +0100

edg1@tiscali.be wrote:

> That's quite impossible, unless there is a serious bug in the driver.
> This type of scanner is pretty dumb and it doesn't move unless the driver
> tells it to move (and the driver never tells it to track back).

Hummm... so you mean, the stepping motor is directly controlled by the
driver? Like bytewise? Wow...

> Does it happen at all resolutions?

I tried with color and BW prescan, and with color, BW & greyscale scan
in 50 and 200dpi... all the same. Sometimes it clanks more frequently,
sometimes less, but I wouldn't say that this is by any means connected
to the resolution or color depth.

> This sounds like a physical problem. The fact that you get similar sounds
> with the Windows driver seems to confirm this.

Ah, I wasn't precise on this one, forgive me. The scanner ran just fine
on Win98 and Win2k... trouble started with WinXP (don't laugh ;-).

> Those vertically stretched regions may be due to the scanner head jamming
> a bit every now and then and jumping ahead when the driving belt tension
> increases. Maybe the glider bars need some grease?

Yeah, I thought that too... but there's two facts against such a thing,
as far as I can see:

1. The noise is *really* loud and *really* precise (hope you know what I
mean, it's hard to describe a sound in ASCII). It's not like the sled
jamming on the slider bars and breaking loose now & then... more like
hitting the case with a No. 8 drum stick. Hard. Precise. Loud.

2. When the head slows down (after 2 or 3 consecutive *clank*), it
apparently doesn't do that due to friction but bcs of the stepper motor
slowing it down (same frequency but smaller spacing). The actual *clank*
noise is not at all correlated with the head's movement. I will try and
show you an example in ASCII (s=step, *=noise):

head moves this way ---->
    *      *  *  *            * *             *      * * * 
s s s s s s s s s s ssssss s s s s sss s s s s s s s s s s sssss....

(sorry it's not actual scale, there are of course many more s between
the *... typical distance between consecutive * is about 1 sec.)

> If your PC were too slow (or too fast, which would be more likely), you
> would probably see other artifacts due to synchronization problems (lines
> having the wrong colors or containing garbage).

OK. I don't have those symptoms. *phew*

Would you encourage me to open that scanner up and have a look? I'm
quite comfortable with electronics... but mechanics?... ummm... still
remember the last time I dismantled a VCR chassis :-/ Any special tips I
should obey?