Replicator MightyBoard Protection Part 2: ESD Protection
From Part 1, we know that Replicator MightyBoards occasionally blow up. One of
the suspected causes of those blow-ups is Electro-Static Discharge (ESD). Part 1
offered some protection from ESD on the EndStop data lines, and in this Thing,
we'll try to improve on that to offer some protection to the Replicator in general.
The most common source of ESD damage is from the human body, discharging an
accumulated charge into a sensitive electronic circuit. You accumulate a charge
via motion or friction with an object. You discharge when touching a conductive
object; i.e., that spark when you touch a doorknob. One of the insidious things
about ESD damage in electronics is that it is cumulative. You might zap your
Replicator, and it keeps on working, so you think you've dodged a bullet. But the
damage may still be there, waiting to accumulate further damage with the next
zap, or just planning to spontaneously distruct at some random time in the
future. And here's another secret: ESD discharges that you may not even feel,
may still damage your Replicator.
There are sort of three general ways to protect against ESD in a system:
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Isolation; by preventing any path for ESD to reach sensitive circuitry.
Shunting; by providing an alternate path to ground for an ESD event by
adding a device to the sensitive circuits.
Interception; by discharging the ESD source before it comes in contact with
sensitive circuits.
... and I should also mention ESD prevention, see the beginning of the
Instructions below.
Isolation is pretty much impossible in the Replicator. While you may think the
wooden case would make this easier, the fact is that there are many sensitive
circuits that are exposed throughout the box, that are easy for a user to come in
contact with. Shunting was done with ESD diodes for the EndStop signal lines in
Part 1, and more will be added to the LCD cable in an upcoming Thing. However,
it's just not practically possible to get an ESD device onto every exposed line in
the Replicator. (Note that the MightyBoard revision used in the Rep2 and 2X has
ESD devices added to every line.)
That leaves interception, which this Thing is going to work on. It may or may not
be attractive, depending upon your POV, but I think it will be a considerable help
in keeping your Replicator safe from ESD damage. So, we're going to wrap a
strip of **conductive aluminum tape** completely around your Replicator, and
ground it. Plus ground the aluminum build plate (if you still use it) and the
aluminum platform arms (if you have them). The idea being, that you will be
likely to touch one of these items before you touch something sensitive in the
Replicator. And, if you remember to consciously discharge yourself at one of
these grounded points, even better.
Note that you may implement this Thing without having installed the EndStopESD
board from Part 1. Note also that installation of this Thing is strongly
recommended before installation of the LCD ESD add-on board that will be
presented in Part 3.
Instructions:
It's always a good idea to practice good ESD (Electro-Static Discharge) prevention
around your Replicator at all times, regardless of any 'protection' you may have
added:
ESD Prevention
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Avoid wearing clothing that generates static electricity.
Avoid placing your Replicator in a carpeted area.
When approaching your Replicator, touch something grounded before you
touch the Replicator.
Be aware that low humidity conditions can increase ESD problems by a
factor of 10X.
Also be aware that unpeeling just about any kind of tape generates an
enormous static charge.
It wouldn't be a bad idea to wear an anti-static wrist band when working on your
Replicator. (Note that so-called “wireless” or “cordless” anti-static wrist bands are
a hoax, and are less than worthless for preventing ESD damage.) To be effective,
the wrist band must be grounded.
Prelude:
In addition to this Thing, you must print and install either the Replicator
Keyboard Cover or the Replicator Front Panel. Both of these Things cover the
ridiculously exposed LCD board, and serve to provide isolation there from ESD.
Note though, that the Keyboard Cover will not fit on the upcoming LCD ESD Thing
that will be posted in Part 3 of these Things. Unless someone steps up to design
a cover that fits the LCD board with the LCD ESD Thing, the simplest choice is
print and install the Front Panel Thing.
Materials:
• Aluminum duct tape, 2-inches wide, about 10 feet. (Note that this is 'real'
duct tape, not the grey stuff - nobody in their right mind would actually put
that on their ductwork.) It's available at any hardware store or Wal-mart;
here's the stuff at Amazon.
• Ribbon cable. 4-to-6 conductors; you'll need about 30 inches.
• Crimp lugs. I prefer to use ring lugs in the MightyBoard compartment, so
that they won't be flopping around if the nut loosens. Spade lugs can be
used elsewhere.
• M3 (or M4) screws and nuts, washers.
Tools:
• X-acto knife and/or scissors.
• Allen wrench to access the MightyBoard area.
• Wire strippers/cutters.
• Drill and bit appropriate for a 3mm (or 4mm) screw.
• Crimp tool.
• If you didn't install the connection to the top of the power connector in Part
1, you need a large soldering iron or gun, sufficient to make that
connection.
• Ohmmeter, DVM, DMM, or whatever you have to measure continuity.
Skills:
You will need to be able to solder a ground wire to the top of the power connector.
Make crimp connections. Apply the aluminum tape.
Printing: Nothing to see here, move along.
Installation:
Note: If you installed Part 1 then items below labeled [Part 1] have already been
done and may be skipped.
1. Remove the power and USB cables and orient your Replicator on end.
Remove the bottom plate to expose the MightyBoard.
2. If you haven't done so already, this is a good time to install the Replicator
Power Cord Support Bracket by DDStarkey. This will prevent damage to the
MightyBoard connector, and will absolutely prevent incorrect insertion.
3. [Part 1] Drill a hole in the Replicator back panel for a ground screw. Right
about through the 'n' in Brooklyn is a good spot. Be careful to not damage
any wires inside.
4. Drill a second hole in the Replicator back panel for another ground screw.
This is spaced vertically above the previous hole, by about 2 inches, such
that the hole enters the build chamber of the Replicator.
5. [Part 1] Prepare a 2.5 inch piece of 4-8 conductor ribbon cable. On each
end, individually strip the ribbon cable wires and twist the wires together.
On one end, crimp a ring lug. Do not presolder the wires in the crimp. If it's
a good crimp you don't have to solder at all; but you can afterwards if you
must.
6. [Part 1] Solder the other end of the cable to the top of power connector
shell. This will require time and the heat of a large soldering iron or gun.
Don't leave any loose strands of wire unsoldered. The ring will be attached
later.
7. Unclip the extruder wiring tube from clamp on the outside back panel.
8. Dismount the LCD board from the front panel of the Replicator. Unplug it
from the cable and set it aside. If you have the board in a Front Panel
Thing, dismount that too.
9. Now we're going to wrap the Replicator with a continuous strip of the
aluminum tape. It needs to be one strip without breaks, so it you mess up,
it's best to just start over - the tape is cheap. Be careful - the tape edge
can be very sharp.
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Starting in the middle of the Replicator side where the SD card slot is,
remove the backing from about 18 inches of the tape and place it so
that the upper edge of the tape is aligned with the lower edge of the
build chamber opening, and so that about 8 inches of the end will
wrap around to the back side. Burnish the tape flat as you go with a
hard smooth object.
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Continue wrapping the end towards the back side. When you get to a
corner screw, remove it, carefully keeping the nut in place. Place the
tape and poke an 'x' at the hole with the tip of an X-acto knife.
Replace the screw. When going around an inside corner, be careful
pushing the tape into the corner - it is easy to tear.
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Finish placing the end of the tape on the back side. You can judge its
position by keeping it a fixed distance above the interlocking tabs of
the case. The end must extend far enough to cover the upper hole
that was drilled in the case earlier. Poke an opening in that hole.
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Continue wrapping the tape towards the front, unscrewing, poking,
burnishing as you go, keeping the tape aligned to the bottom opening
of the build chamber. For the moment, tape right across the LCD, SD,
and button openings.
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Continue around the front, side and back. Trim the end of the tape so
that it will finish over the 'B' in Brooklyn but don't lay it down yet.
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Fold the end of the tape under, sticking it to itself, such that the folded
area will fall over the hole that was drilled. The fold is necessary so
that the aluminum surfaces will be in contact, making an electrical
connection. Poke an 'x' over the hole.
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If you're like me, and I know I am, strip all of the tape off and start
over, 'cause you weren't satisfied with the first effort.
10. If you have already done Part 1, and have a screw installed in the lower
hole, remove it now.
11. Cut a strip of tape about 3 inches long and one inch wide. Remove the
backing and fold over about 1/2 inch on each end. Place this strip so that it
spans the two new holes on the back side, such that the folded areas are
over the holes. Poke both of the holes open.
12. Place a screw with washer in the lower hole and a nut on the inside and
tighten. Place the ring lug from the cable from the power connector over
the screw, (and the cable from the EndStopESD board if you've done Part
1), add a jam nut and tighten.
13. Place a screw and washer in the upper hole, add a nut and tighten loosely.
The washers are necessary so that the head of the screws don't tear the
tape. We didn't care about the case screws, because those connections
weren't electrical.
14. You now should have a continuous band of tape around the Replicator,
electrically joined at the ends by the fold and screw, and electrically joined
to the lower screw by the short strip of tape, and ultimately joined to the
power connector ground by the inside ground cable. Rinse and repeat as
necessary. We're just gettin' warmed up.
Perform the following steps marked [BWA] only if you have Bottleworks aluminum
arms installed.
15. [BWA] Cut an 8 inch length of ribbon cable. Strip the ends and twist the
individual wires together; do not solder. Crimp a spade lug on one end.
16. [BWA] Cut a 14 inch length of ribbon cable. Prepare the ends and crimp a
spade lug on one end. Take the unfinished ends of both cables, insert them
into a single spade lug, and crimp.
17. [BWA] There are two screws on each side of the aluminum arms that
attach the platform to the arms. Loosen (do not remove) the rearward
screws on each side. Place the cable spade lug [8 inch end] under the left
arm screw and tighten. Route the cable over the arms and behind the build
plate, and place the middle spade lug under the screw on the other side [do
not tighten]. Place the lug on the other end of the cable under the nut on
the screw that you added from the tape wrap, and tighten. A strip of the
aluminum tape is good for holding the cable flat on the top of the platform.
18. If you are not using your aluminum build platform, skip this step. Prepare
a 2.5 inch ribbon cable with spade lugs on each end. Place one end under
the right side platform/arm screw and tighten. Connect the other end to
the right rear heater board/build platform screw.
19. If you have an aluminum build plate and no BWA, prepare a 14 inch cable
with spade lugs on both ends. Connect one end to the right rear heater
board/build platform screw. Place the lug on the other end of the cable
under the nut on the screw that you added from the tape wrap, and tighten.
Do not run this cable in parallel with the HBP electrical cable.
20. If you do not have a Front Panel Thing, trim the tape around the LCD and
button openings. It would be best if the tape did not touch the LCD bezel.
Remount the LCD board. Also trim the opening around the SD card slot. If
you have a Front Panel, you only have to trim the tape in the button area
enough to get the ribbon cable through.
21. If you have the Front Panel, add strips of aluminum tape to the top of of
the panel, above the LCD and button; fold it over the back edge. Likewise
place a strip on the end around the SD card opening. Replace the Front
Panel.
22. Unplug your power brick from the wall, and plug in the power cable from
the brick to the Replicator. With your ohmmeter, measure from the ground
prong on the AC plug, to various points on the tape you've just installed.
Also measure to the build plate, aluminum arms and tape on the Front
Panel, if you have any of those. All of those points should essentially be a
direct short to the ground prong.
Final Notes: There are all kinds of ways you could accomplish this differently, but
here are a few points to remember:
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The flat tape is a very low impedance path to ground, better than a single
wire.
The ribbon cable's multiple conductors offer lower impedance than a single
wire.
Avoid routing any ESD ground cable parallel to any signal or power cables,
or near the MightyBoard.
Note also that there will be a Part 3 and 4.