I suppose I didn't expect much help from them, but their attitude has 
been go away & don't bother us.  Quite a shame, really, because they
make a great product.  However, I could never recommend them to
anyone after this.

There are no obviously overheated chips, nor caps for that matter.
But then tantalums either show no changes, or else crack open if they 
get hot enough.  I had planned to go over the controller card looking
for the changing voltage, and then following it back to the source. 
However, that would be a whole lot easier with a schematic to follow.

As for releasing schematics, I have never really understood the issue.
In the case of a scanner, most of the complexity and cost is likely to
be in the optical hardware, and ultimately the firmware controlling the 
hardware. If I wanted to clone the scanner it would take me longer, 
and cost a lot more, to duplicate the optical hardware & the firmware 
than to simply copy the circuit board. 

I have designed many electronic products, and in all cases the hardware
(configuration & packaging) were far more important than exactly 
which chips were on the PCB.  And, in many cases, even if you make an 
exact copy of one of my PCBs, you would still have to have a way to
duplicate/copy the embedded code to make it work.  Not that that can't 
be done, of course.

Let this be a warning to designers - don't rely on an external plug-in 
regulated supply alone to protect your hardware. Especially when using 
a standard plug & jack pair as would be found on any unregulated wall 
wart. Had this scanner had a voltage regulator on the main board, or a 
different type of power plug to the regulated supply, it would not have 
mattered if the wrong wall-wart was plugged into it. The regulator might 
have gotten hot and gone into thermal shut-down, or maybe popped a fuse. 

RJG

> ----- Original Message -----
>
> From: "Robert Rolf" <Robert.Rolf@ualberta.ca>
> To: "Microcontroller discussion list - Public." <piclist@mit.edu>
> Sent: Wednesday, May 11, 2005 10:32 PM
> Subject: Re: [EE]: looking for schematics or other info on Microtek
> 4900scanner
> 
> 
> > Roy J. Gromlich wrote:
> >
> > > I am asking this question here because I am getting
> > > absolutely nowhere with Microtek.
> >
> > You expected otherwise?
> >
> > > I have had a Scanmaker 4900 for about two years -
> > > was working great.  In the process of moving it to
> > > another computer it was accidentally powered from
> > > a 12 volt wall wart instead of the proper 12 volt
> > > switching supply.  The switcher is apparently
> > > regulated, while the wall wart wasn't, and probably
> > > went above 12 volts.
> > >
> > > Since then, even though connected to its proper power
> > > supply,  the scanner has not produced its usual beautiful
> > > scans - they are washed out and get more so the longer the
> > > unit is turned ON, until after 2 minutes there is nothing.
> > > Obviously something was zapped by the overvoltage.
> >
> > Check for chips that are overheated. Try
> > cooling them individually with freeze spray to see
> > if it's a chip or a tantalum cap (the cap is more likely).
> >
> > > Now Microtek wants a Lot of money ($80 to $100) to
> > > fix it - I can buy a new one for that amount.  I asked
> > > them for schematics so I could take a crack at it, but
> > > no go - I was told it was too difficult to take the case
> > > apart without breaking it.  Actually, I popped the case
> > > off in about 3 minutes - nothing broken. I informed them
> > > of that fact and was advised to call their professional
> > > consultants - at $30 per call.
> > >
> > > So here is the question - does anyone out there, by some
> > > strange chance, have schematics for a Microtek 4900
> > > scanner?
> >
> > If they do, they'd be forgeries. This kind of information
> > is NEVER released by a manufacturer. As far as they are
> > concerned these devices are 'not repairable'.
> > The $80 repair charge is for a 'new' logic board or
> > whatever since as you noted a complete new scanner costs
> > as much.
> >
> > > Or even a close model 4800, 4850 ?  I know
> > > the chance of this is very small, but I figure it can't
> > > hurt to ask.
> >
> > You would have more luck asking for winning lottery
> > numbers.
> >
> > R
> >
> >
> > --
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> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> 
> 
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