Posted for "Bruce" <BGray@glasair.org>:

 Cross post from Glasair.org:
 
 
From: "Reggie Smith" <mooney37v@juno.com>
 
 Vision Microsystems VM1000 & EPI800: What version do I have?
 
 This is the 4th in a series of posts about the Vision Microsystems (VMS)
 VM1000 and EPI-800 engine management systems. As a reminder, I'm not a
FAA certified avionics technician, just an avid experimental aircraft
 enthusiast and EAA member passing along what I've learned to the
 community that's given so much to me. This post will cover the different
 versions and evolution of the VMS product line and provide some tips for
 keeping each system healthy and reliable.
 
 The "first generation" VMS system was the EPI-800 with a 1987 copyright
 date.  The data processing unit (DPU) was a screw terminal type that was
 the blueprint for all subsequent DPUs until 2001 (see pic #1). The first
 generation DPU had a number of limitations all addressed in later
 versions. One of the most important aspects of the first gen DPU was
 that it was not easy to repair because the digital and analog PC boards
 were "hard soldered" together via a set of central connection pins in
 the middle of the DPU case; separating the two boards requires tedious
 desoldering of the central pins. Also in the first gen DPUs, there are
 no jumpers. Junctions are "hard jumpered" via soldered link so changing
 such parameters as pulse count for magneto vs. electronic ignition RPM
 sensing is difficult at best. First gen DPUs are generally plagued by
 delamination issues most commonly on the analog board but can also be
 found on the digital assembly as well. You can easily identify a first
 generation DPU by removing the analog board cover (cover with the
 cutouts for the screw terminals) and look at the pins running from the
 board into the DPU center.  If these pins are flat and covered with what
 looks like opaque tan masking tape, it's a first gen. Don't despair if
 you have a first gen, they still work fine but may require more labor to
 repair than later versions.
 
 With the introduction of the VM1000 in the early 1990s, came upgrades to
 the DPU and starts the "second generation." First upgrade was the
 replacement of hard soldered analog to digital connecting pins, with a
 header pin and connector setup.  Header pins were soldered on the
 digital board and a receptacle assembly on the analog board (see pic
 #2). Now the two boards can be easily separated for repairs.  However,
 many of the early VM1000 DPUs still had "hard jumpered" junctions making
 changing options in a DPU difficult.
 
 It was not until the mid 90's that selectable jumpers were installed on
 the digital and analog boards starting the "third generation" DPUs.
 These final modifications to the boards became the standard
 configuration until the next major changes in 2001.  These 3rd gen
 boards are identified by C 1992 REV D on the analog board and C 1995 REV
 H on the digital board.  These boards also have high quality etching so
 there are no issues with delamination as in the first and some of the
 second generation units.
 
 As owners will attest, screw terminal DPUs have their limitations. In a
 tight installation, the screw terminals can be difficult to properly
 torque. Wires have a tendency to loosen or break at the terminals and it
 is easy to insert the wires too far and clamp down on the insulator
 instead of the conductor resulting in an intermittent connection and a
 frustrating time troubleshooting an indication problem. But with
 knowledge of these limitations, and making the DPU and the screw
 terminals part of your annual condition inspections, owners can get good
 service from their systems.  A simple torque check using a jeweler's
 screwdriver and gentle tug on each connecting wire should be all that's
 needed to ensure a good connection.
 
 In 2001, VMS introduced a new version of most of the system components
 including the DPUs, displays, and sensors for both the EPI-800 and
 VM1000. The VM1000 also became certified under TSO-C113 and installed in
 several type certificated aircraft including the Symphony OMF-160 and
 Liberty XL. The great aspect of this "fourth generation" is all of the
 components are backwards compatible with all previous systems. Most
 notable, on the DPU gone are the screw terminals and are replaced by two
 serial type connectors, a single 25 pin RS-232 type DSUB connector which
 handles all the EGT and CHT signal inputs, and a single 37 pin DSUB
 connector which handles power and all other sensor inputs (see pic #3).
 This makes for a neat, tidy, and easy to service installation and vastly
 eases the work required to remove and repair the DPU.
 
 However, installation issues can compromise even this almost bullet
 proof connection scheme.  Many experimental aircraft installations have
 the ideal geometry where connection cables from the firewall proceed
 directly into the DPU, a straight connection which induces no side
 loading on the DSUB connectors.  The DPU is installed on the instrument
 panel with the receptacles facing toward the firewall; these
 installations typically have no issues with connectivity.  Other
 installations have a 90 degree geometry, cables come into the cabin then
 turn parallel to the firewall and connect to the DPU.  If properly
 supported, this is also a good connection scheme with little problems.
 However, fail to properly support the cable runs, and there's a
 possibility of excessive vibration or resonation of the assembly which
 eventually results in connections problems at the DPU and resultant
 display issues in the cockpit.  The worst case scenario is illustrated
 in the Symphony OMF-160 installation in which the signal cables come
 through the firewall, make a tight radius 180 turn and connect into the
 DPU with little to no support other than the DPU connection itself (see
 pic #4).  Symphony owners have reported significant issues with display
 problems traced down to connection issues at the DPU.  Vibration and
 resonation of the cable assembly can wear down the internal pins and
 sockets inside the DSUB connectors to the point that the contact becomes
 intermittent and may eventually break the solder joints of the DPU
 connectors.  Check your installation to make sure your signal cables are
 properly supported and have an appropriate radius for any turns.
 
 The 4th generation systems were also available with some customization
 not previously available.  For example, one version of the VM1000
 included a "% Power" indication in place of the manifold pressure for
 single lever FADEC equipped aircraft.  Another version was setup to
 output RS232 digital data to GPS units.  However, the baseline EPI-800
 and VM1000 systems in the experimental market still seemed to dominate
 the bulk of sales and production with Lycoming O/IO-320/360 series
 setups for Glasair I & IIs, RVs, two place Lancairs, and many others;
 Lycoming IO-540 series for Glasair IIIs & F-1 Rockets and Continental
 IO- & TSIO-550s for the Lancair IVs and many others.
 
 The 4th generation represented the final iteration of the venerable
 EPI-800 and VM1000 product line ... the next product, the VM1000C was
 essentially a clean slate design eventually acquired and improved by JP
 Instruments. If I can help with any Vision Microsystems issues, please
 feel free to email at mooney37V@juno.com
 
 Happy Flying,
 Reggie
 Glasair I-RG Flying!
 Mooney M-20E SOLD
 Grumann Yankee SOLD