Michael Swanson seems to be looking for a MK4 scanner board [161008
MMDigest].  While this was a good system in it's day, finding a decent
reliable computer and associated hardware with the necessary parallel
port can be problematic.

Most electronic/computer hardware has about an average 7-year lifespan
due to the aging of the electrolytic capacitors ("condensers" in the
UK) in the power supply systems.  This is well known in audio work
where aged caps can cause distortion.  With computers the problem is
less obvious as it causes the digital logic power to operate outside
the voltage range specification.

This is more severe if the older device has not been turned on for some
time. In this case the caps can short out and blow the circuit boards.
This is well documented on the vintage retro-computing sites.  As the
7-year lifespan is an average, it is not uncommon for old computers
(especially if run 24/7) to run 20 or more years.

The choices to keep stuff working are split into software emulation/and
update to a modern hardware interface.  Upgrading to a modern interface
should not be much trouble.

Years ago I posted here in the MMD archives a USB version of the
MK4 which uses the same processor as the popular "Arduino" interface.
I have been using this setup for over a decade or so.  The "Arduino"
system works with boards that plug on top of it like Lego bricks.
(The Lego Mindstorm system actually has the same processor in it.)

These plug in modules are called "Shields."   There is a new term
called IoT or "Internet of Things" which is part of the "Shared Economy."
Find kids under 30 and tell them that the roll scanner is a robot and
they will understand this stuff intuitively.

Roll scanners are part of the IoT ecosystem.  It is easy now to get
circuit boards made by using one of the shared board manufactures like
OSH Park or Gold Phoenix (China) or Sunstone/ExpressPCB (US domestic.)
I did the USB version of the MK4 with ExpressPCB.  These layouts are
stored on the MMD in the archive under 'USB Controller for CIS Optical
Roll Reader' at http://www.mmdigest.com/Gallery/Tech/USBCIS.html 

The companies that now make PC boards need something called Gerbers.
When the design is uploaded anyone can order that board.  So if the MK4
was converted to Gerber and uploaded to OSHPark or ThingVerse, then it
would be easy to order a board direct the same way as one uses AirBnB
or Uber.

In practice I would not recommend using this layout as is, some of
the chips have been updated.  Things have become a lot "simpler" in the
last decade.  A full tricked out "Arduino" starter kit costs around $30
USD for the "official version" and clones can be had for a few kopecks.

It is easy to connect a Dynascan array (probably harder to find than
a MK4 board) to an Arduino.  If there is desire, I can provide Gerbers
for a direct "shield" interface.  Most kits, however, come with some
6- or 10-inch jumper wires that are included that can connect directly
the same as the MK4 if one already has the scanner array.

The older layout on the MMD Archive has four sections.  The top is the
"Arduino"; below are three small sections that are cut off.  One is the
power regulator. In the middle is the scanner lamp controller for
setting the lamp brightness.  The far right contains the connectors to
the array.

When I designed this I used the parallel chip as the MK4 was parallel;
now the "Arduinos" use a serial bridge chip which is even better.  So
all one really needs is the connector board and the back light
controller.

The second part of using an old interface, on new hardware, is Software
emulation -- specifically, DOS emulation.  Most people who are into
retro computing like DOS to play computer games.  There is an excellent
DOS emulator called DosBox that emulates about Windows 3.1 and possibly
Windows95.  I had to get this to run a pipe organ & setup programs
under windows 8.  DosBox also has versions for MacOSX and Linux.

DosBox will emulate the COM port on the "Arduino" so that the old direct
write to COM port register programs work again.  DosBox does not, as
I last checked, emulate a bit-banged parallel port.  It will run the
old Basic programs such as were used to capture the raw roll scan data
that create a CIS file.  Arduino uses Sketches to program with an easy
to use interface for blinking LEDs and controlling shift registers
(which is what the Dynascan array is.)

Julie Porter
California