Tools for PDP-8 repair
There seems to be some kind of persistent internet "meme" that
you should use old test equipment to fix old computers (or
radios). Bullshit.
So this is a list of tools that either (a) you didn't know you
needed or (b) you knew you needed but you either have or would buy the
wrong one. It doesn't include things like screwdrivers because
(a) you already knew you needed them and (b) there are few bad
screwdrivers. So substitute at your own risk. As an
example, when I suggest that you need Polyphenol Ether contact
lubricant, I don't mean that you should go to Fry's and buy contact
lubricant because the generic idea of "contact lubricant" is good, I
mean exactly Polyphenol
Ether contact lubricant is good.
This page is all about doing things correctly with the right
tools so they will last. If you are the sort of person who uses
car motor oil to lube your teletype because it's "good enough" this is
the wrong page for you.
Am I
missing something? Write me, nabil AT pdp-8.org.
Teletype Tools
I have a large collection (200+
items) of small teletype hand tools (including many for 5-level
machines), so if you are local and need
something special feel free to contact me for a loan. There must be
lots of things to bend in a teletype because a 1/3 of them are various
kinds of benders.
Crochet Hooks
These were sold by Teletype as
"spring pullers" and a very
handy for hooking and unhooking the small springs.
Needle
Oiler and 3-IN-ONE Motor Oil
You
should really use a pin-point or needle oiler, you want to minimize the
excess oil drippings which will attract dirt. Cheap needle oiler
bottles are
commonly available from firearm tool dealers (get one with a very long,
very
thin needle). For the general use KS7470 oil 3-IN-ONE Motor Oil
(blue bottle) is a reasonable commonly-available turbine oil and
certainly
safer that any of the other crap people
suggest like car motor oil or WD-40. The 3-IN-ONE
motor oil is a hydrocracked paraffenic base with corrosion inhibitors
which seems to be close to the military substitute (a paraffenic
turbine oil) of
the original KS7470. I own 4
pints of original KS7470 teletype oil but usually just use the 3-in-one
oil instead. It smells different than the teletype oil but it's
not unpleasant. If you are have the time to do the research
a pure synthetic oil could probably be found with
better properties, for example the Nye
Synthetic Oils, but many of these synthetics can attack the
plastics in a teletype. I occasionally use a synthetic
spindle oil w/PTFE on a part of the keyboard because of the low return
force involved.
For the KS7471 grease I and many other people use
Lucas Red 'N' Tacky #2 but without much analytic justification other
than experience. Note that some of the teletype lube instructions
require mixing the oil
and grease 50/50 so you'll want to test the pair for compatibility.
Atlantic
Research Corporation DTS-1/Data Tek 9600
These are serial terminal test
sets geared towards teletypes. The
most used bit is the pattern generator (several test
messages and a programmable 4 character custom sequence for test loops)
with selectable code level/bits (ascii/ebcdic/baudot) and
distortion. On the receive side there there is also a
one-character
receiver (on LEDs) and several extremely useful things for teletypes
like a loop current meter and distortion analyzer.
They'll do 20ma/60ma/polar current loop & RS-232 (which has a nice
little patch and switch section). There are a couple versions, one with
an EEPROM on the front for custom
test message and one without (there is no advantage to the EEPROM
version). They are the first tool I go
looking for to work on my teletypes.
At one time I bought one that had some kind of factory modification
done to it, it was the highest quality work and involved adding another
circuit board (3 transistors, a hex inverter and an optoisolator), the
front panel had the topmost loop output plug replaced with a BNC
connector and 3 binding posts installed above the RS-232
connector. I'd avoid buying one with these modifications.
I have several of these, contact me if you are local and need to borrow
one.
Tygon/Plastic/Rubber
tubing
for
replacing
model
33
hammers
Every 33 hammer I've seen is
gooey
and must be replaced. Even the
box of factory new hammers I have hammers is gooey! These will
deform rapidly causing the metal striker to hit the type wheel, quickly
destroying it. The best solution is to remove all the hammer
residue
and get some rubber or plastic (I use a soft plastic) tubing the fits
snugly over the metal striker. You are trying to match the
original (quite thin) dimensions, so don't get something so stiff and
tight that it bows up, get something reasonably soft and
conformal. Cut it quite short (1 cm) to minimize the mass. People
will suggest all kinds of other things like rubber bumpers, but when it
falls off because the adhesive fails and the striker hits the typewheel
you are instantly and irrevocably screwed.
General Tools
A modern soldering iron
If
you are like me, you have a Weller
WTC-series soldering iron somewhere on your workbench. These were the
mainstay of the industry, and used a curie-effect temperature
regulation system (each tip programmed the iron for a different
temperature). They were low-voltage, grounded-tip, and reasonably
safe (for a sub-$200 iron).
Times have changed, it's time to
get a new iron. Although the
newer generation of the WTC series started incorporating better
ESD protection, they couldn't eliminate a fatal design flaw, and
that was the arbitrary times when the heater kicked in and out,
creating a EMF spike which can be coupled into your workpiece.
Weller makes several new irons that
use zero-crossing
(electronic) control along with much better ESD control and
protection again stray currents and fields. The EC series is
nice, and ranges from $200 to $400. The Weller 921ZX1 is an
inexpensive alternative (I picked mine up at Fry's for under
$80). It has a slide control for setting the temperature (in
degrees, not "watts", which is useless like the cheap ones), and
reasonable selection of tips from the beefy to SMD. A nice
feature is a bi-color LED which monitors the heating circuit's
power output ratio. The picture to the right is the 921ZX.
If
your
soldering iron isn't temperature regulated
it's useless for
computer work.
If you can find a used one Metcal irons are very nice.
Avoid:
Cheap
unregulated
temperature
irons,
non-ESD
irons,
arbitrary
thermostat
irons.
The
921ZX
is
good and inexpensive.
Edsyn SoldaPullt
Solder braid is handy, but these
are simply the most useful piece of
desoldering equipment. The full-size ones are the best, get one
of the ESD safe versions, not the blue one. Indispensable.
Squeeze-type
IC Lead Straightener
Most straighteners are from bad
to useless, this one is by far the
best of the ones I've used. Radio Shack used to sell them, Jameco
has them now. The other side is for 16 pin DIPs. It's
conductive plastic, you just drop the chip in and squeeze.
Service Chemicals
DeoxIT (the red ones)
DeoxIT is a group
of service chemicals for
restoring electrical contacts & plated connections. It
is reactive, and actively removes corrosion and oxidation.
It is also somewhat persistent, and will remain on connectors
that
are mated and unmated, moving wipers, etc. DeoxIT is well known,
recommended by several OEMs, and generally compatible with most
materials. Personally I only use it when I'm dealing explicitly
with corrosion, oxidation or on high-current applications (like power
supply connectors). Deoxit is especially vital on high-current
mated molex power connectors where an I^R/mechanical thermal runaway
effect routinely destroys them, for example the J4/J5 power connectors
and fuse holders in an 8E, but you need to do it before the damage
starts! There are several concentrations from 5 to 100% for
various applications, I'd stick with the low concentrations (the base
product is an oleic acid derivative) for splashing around.
Spraying a bunch on a clean rag and then using that to clean off
dull-looking card edges seems particularly effective and leaves some
behind to clean the mated connector.
Avoid:
WD-40. Any
other
contact
restorer.
Using
too much, using on uncleaned
contacts, using on things that are exposed and can attract dirt.
Polyphenyl
Ether contact lubricant
I use this to
make card insertion easier but
these can also reduce contact resistance (a lot!). If the product
is pure PPE & carrier there is really no downside to using these on
any high-insertion force connector, they can only help. Very handy for OMNIBUS
cards (spray on the card, not the backplane). PPE is
a very
light
lubricant, non-reactive, non-conductive and typically with few
compatibility or contamination problems. It must be replenished
if you do frequent insertion/removal cycles. The 6-ring version is a
little more viscous and a little longer life. Specifically avoid the
"wipes" products, they leave little strands of the pad
stuck to the sharp bits of a card edge which are a real hassle to
remove. Just get the aerosol spray or liquid (not pure, 2%). Use is
simple, clean the
contacts first if they are dirty, spray the PE on, let it dry.
For those of us with the
occasional brush with
modern computers it's also what I use on big pin count packages
like Intel 486's when the need to go into a normal (i.e., not ZIF)
socket. MG Super Contact
Cleaner and Techspray Rid-Ox
are two industrial grade products you could try, but there are also
"purer" aerospace/aviation grades. You want one that evaporates
completely without any extra oils or junk, I liked the Chemtronics Gold Guard as it only
had alchohol and PPE in it, but I'm not sure if it's made anymore.
Avoid:
Anything
except
Polyphenyl
Ether
contact
lubricant. Any of the
'wipes' products.
Heptane label removers: Original Un-Du and
Bestine
They are 100% Heptane which is
absolutely the best label remover. It has relatively low toxicity
(nor has it been
identified as a carcinogen) and is compatible with most surfaces and
materials, including plastics. Un-Du has a very nice scraper, so
if you can find an original bottle, get one. Bestine is much
cheaper, from 1/2 to a 1/4 the price, but it doesn't come in the little
dropper bottle or scraper. Until you have tried Heptane as a
label remover you can't even begin to appreciate it, there is no
comparison, it's not "a little better" or "20% better", it is 1000%
better. The downside is it's almost
instantaneous evaporation that can make it difficult to to use.
Avoid: Reformulated
(California, VOC safe) Un-du. Anything with xylene, toluene,
benzene, acetone or methylene chloride in it. I like to avoid
methanol (methyl alcohol) as much as possible. Goo Gone Xtreme
Remover (toluene, acetone & methanol) would be top on my 'avoid'
list, but it probably works great.
Logic Tools
HP E2310A LogicDart
It’s a small,
hand-held 3-channel logic analyzer (or small digital scope) with an LCD
display, the nice thing
about it is that you can program the logic threshold, so it can
be used on things like ECL and negative transistor logic
computers.
Very light, it's reasonable to use as a logic probe (nice
lights and beeper), I particularly like the needle-sharp probes.
Discontinued,
but HP still has this
data
sheet online.
Avoid:
Buying these without the special probes, they are useless without them.
Tektronix
P6401 Logic Probe
Mostly I use my LogicDart, but a
stand alone
logic probe is very handy, especially one that is easy to read like the
Tek with it's bright, omnidirectional red and green lamps right at the
tip. The "memory" is easy to use and inuitive, it allows you to
catch a transition without watching the probe. The Tek uses
incandescent lamps, only
TTL/DTL and not very electrically rugged but I have yet to find any
other that is the perfect combination of
functionality, size and ease-of-use. If you are searching for one
on
ebay, don't accidentally get the version with the BNC on the end, the
one you want has a red and black power clip.
The HP 545A would
be
my
second
choice (has a long sharp tip & CMOS mode)
but the
indicator uses OFF/DIM/BRIGHT instead of Tek's RED/GREEN. It's
long, thin body can be an advantage over the Tek's short stubby one but
I still prefer the Tek, the performance and human interface is just
perfect.
If you are using a logic probe you don't want to be thinking about it
how to read it, you just want it to be a transparent little
visualization of the circuit node. That's what the Tek is.
Avoid: Probes where
the indicator is on one side or can't tell the difference between "not
hooked up" and
"low". Logic
probes
with
LEDs
on
the
top
of
a
flat
box are just silly.
HP 548A Logic Clip
"The Logic Clip is an extremely
handy service and design tool which clips onto dual-in-line package
(DIP) ICs, instantly displaying the states of up to 16 pins. Each of
the clip's 16 LEDs independently follow level changes at its associated
pin. Lit diodes are logic High, extinguished diodes are Low."
The HP catalog says it best,
"extremely handy". A few other companies made these but they are
2-3x the size and clumsy.
I have several of these, contact me if you are local and need to borrow
one.
HP 10529A Logic
Comparator
"The HP 10529A Logic
Comparator clips onto powered TTL or DTL ICs and detects
functional failures by comparing the in-circuit test IC with a known
good reference IC inserted into the Comparator. ... Any logic
state difference between the test IC and reference IC is identified to
the specific pin(s) on 14 or 16-pin dual in-line packages on the
Comparator's display. A lighted LED corresponds to a logic
difference. Intermittent errors as short as 300 nanoseconds (using the
socket board) are detected, and the error indication on the
Comparator's display is stretched for a visual indication. ..."
If that isn't clear enough, you
clip onto a chip, the inputs
go to the inputs of your known good reference IC, the outputs are
XOR'd with the outputs from the circuit and displayed on a
display. If you see a light, that node in the circuit isn't
following your reference chip. Reference chips are on little
carriers you program (by drilling!), you can build up a library
of common devices for your system(s) of interest. There is also a
generic card which can be programmed by dip switches for one-off
tests. These often came in kits like the 5011T with logic clips
and probes.
I'm building up a library of
pre-programmed cards for common
PDP-8 TTL chips.
Blank reference cards are HP part
#10529-20005, a package of
20 was available as model #10541A.
I have several of these, contact me if you are local and need to borrow
one.
Avoid: Paying too
much. Just be patient, you can probably get one for $30 or less.
HP 546A Logic Pulser
Pulls a logic node to a different
state. The trick that make a pulser possible is that it uses a
very short pulse (500ns), hopefully not enough to blow up the output
gate of whatever it's fighting against. Without a pulser you are
stuck with the natural state/signals in the device, a pulser allows you
to inject your own, and are commonly used with a current tracer or
logic clip/probe (they have built-in pulse stretchers to make the short
pulses visible). The 546A is nice because it can inject a fixed number
of pulses or a pulse train, is TTL/CMOS selectable, and is also
auto-polarity (it'll pulse the line the "other" way).
General Circuit Testing
HP 547A Current Tracer
“The HP 547A Current Tracer is a
hand-held probe which enables the precise localization of low-impedance
faults in electrical systems. The probe senses the magnetic field
generated by a pulsing current internal to the circuit or by current
pulses supplied by an external stimulus such as the HP 546A logic
pulsers. Indication of the presence of current pulses is provided by
lighting the indicator lamp near the current tracer tip. Adjustment of
probe sensitivity over the 1 mA to 1A range is provided by the
sensitivity control near the indicator. The probe is self-contained and
requires <75 mA at 4.5V to 18V, from any convenient source.”
I don’t use this very often, but
when I need it, I really
need it. It’s used for finding things like shorted input
gates, stuck tri-state buses and broken/shorted traces.
I have several of these, contact me
if you are local and need to borrow one.
General Radio (GenRad) 2220 Bug Hound
This is similar to the HP 547A
current tracer except that it
contains it's own current source and the probe has directional
indicators that let you know which side of the probe the wire is
on. This is very handy for tracing wire-wrap connections. It also
has some other milliohm continuity/tracing functions.
I have several of these, contact me if you are local and need to borrow
one.
Zero Beeper
This is a continuity tester that
uses an extremely low voltage
(say, 100mV) so
that it won't turn on any of the semiconductor junctions in a circuit.
I haven't
seen many around recently, but Contact East (a good source for almost
every tool
on this page) private labels one, the Zero-Current
Audible
Continuity
Tester. It is a must
have tool when you are trying to trace out continuity on a
circuit board.
Avoid: Any other
kind of continuity tester for PCB work. Never use
the Ohms, Diode or Beeper function on your DMM to measure
continuity on a circuit board!
Huntron Tracker 2000 (or similar)
This is sort of an in-circuit
curve tracer who's use is more "art" than
"science". Mostly
for
power
supply
repair,
especially
switchers. It displays
a current vs voltage plot and with a
little practice it's easy to recognize the patterns of good components
and common failures. Has some applicability for testing
passives and small junction devices, I wouldn't recommend using
it on ICs even though many people do. They can be expensive, used
ones easily fetching over $500. There are trackers other than the
2000, but it's the one most commonly available. The 2000's "low"
range is a bit overpowered, the newer models have more usable low
ranges. There are a few "huntron like" devices, Vu-data
and Tenma
make one, and I've seen an
inexpensive ($200) LCD model on Ebay. There are also standalone
boxes that turn an XY scope into a Huntron-like tester. If you
are doing lots of switch-mode power supply repair you might also
consider getting a ringer like the ones built into the Sencore Z-meters
or the Blue Ring Tester.
IC Test Clips
If you are trying to diagnose a
logic problem you'll often be
struggling trying to keep 20 grabber leads in a rigid precise
arrangement so the hooks don't pop off and/or short
out adjacent pins. What you
need are a Chip Clips. This is something that looks like a large
clothespin that you clamp around the chip, with it you can access each
signal via is a pin that is routed to the top of the clip without any
danger of shorting. 3M, AP and Pomona all
made
Chip Clips (or "IC TEST CLIPS"), I like the 3M gold plated ones.
They
are commonly available in the $5 to $15 range. Ones with pin
numbers
are nice. There is a trick, you cut the little plastic
plates used for wirewrapping that have pin numbers on them in half and
put a half on each side, then you have pin numbers. Note there
are two styles of top pins, one with
what look like nail heads (best for manual grabbers/scope probes) and
ones that are straight. The straight ones are handy for use with
logic analyzers as you can slide a standard connector right onto them.
Tek Scope Current Probe (for core memory repair)
Only absolutely required if you
are fixing core memory, but they can be
useful just to tune it. You want the tiny, tiny little sensitive
ones. There are a couple versions, AC only and AC/DC, I think you
only need the AC which are much cheaper (mine are AC/DC and require an
external TM500 amplifier). I'm sorry I'm not recommending a
specific model, check the docs of what you are working on for the
bandwidth and sensitivity requirements. P6022 shown, check out
the P6021 also. About $200 on ebay. For the straight-8
there is a rather rare single-height extender card with individual
current loop wires. On the older OMNIBUS core there is a little
wire loop (which was removed in the last revision).
Transistor testing
The one built into your DMM is
crap. Forget about using curve tracers as transistor testers,
it's not practical. The cheap little LCD parametric (DY294)
testers are equally useless as in-circuit testers, and in circuit
is a must. (For out-of-circuit testing and
identifying is the Peak
Electronics DCA55 is good.) Avoid the 1950/60 vintage
testers, things built into tube testers or more simply avoid
everything that isn't on this list, Note that in-circuit
testers are better at some failure modes than others, parametric shifts
(like excess leakage, which often gets worse) might still test good
in-circuit. Fortunatly transistors usually just fail "busted" and
a simple in-circuit test is all you need.
NB: I removed the Sencore TF46 since people are using this guide
to select which piece of test
equipment they are buying for a particular task The TF46,
although good, was inferior to B&K and no comparison against the
Vu-Data & Leader. The Seccore switches are just too flaky,
the
520B seems to be able to do in-circuit better and the TF46 uses
really crappy, thin wired-in leads (which are always breaking at the
ends) instead of
banana jacks. I'm sure some
people prefer the TF46 over the
B&K.
B&K 520B
(common)
Lead permuting is a 6-step rotor,
PNP/NPN
identification is automatic. These seem to be able to do a
better job on in-circuit devices shunted with low impedances than the
Sencores because of their test method and their high drive range is
quite high (250ma, 4% duty cycle). I like and use my
Vu-Data and Leader much more than the B&K, but it's solid, commonly
available and works well. Note the parametric test is leakage
& Si/Ge, not gain, this is fine for computer work.
Vu-Data 5110
(hard to find)
This is an older (circa 1990)
tester from the Navy. Typically
they'd come in a padded bag and would often include probe sets (bed of
nails and clips), fuses, spare sockets and a
manual. Although complex, they are rugged electrically and
easy to repair using only standard parts. AC powered only. In
addition to the in-circuit tests they have an almost entirely
independent, parallel parametric section (including Si/Ge
identification). These have several features I like: a
continuously variable
drive for in-circuit tests, a display for the permuter
(there is a digital display that shows E B or C above each lead as you
rotate the switch) and of course a beeper. An unusual function
is
the ability to detect several shorted/open-device failure modes
in-circuit
and identify them. Each lead of the
in-circuit tester side is
individually fused and it claims to be able to withstand up to 600v of
accidentally applied voltage. Here's a local copy of the manual.
I have a couple of these, contact me if you are local and need to
borrow
one.
Leader LTC-906 and LTC-906A
(very hard to find)
This was the first transistor
tester I used as a teenager in a professional repair capacity. I didn't
think much about it at the time, it was just the one on the
bench. In the dusty eBay LTC-906 I have the date codes are 1977
which means they predate even my early experience with them by yet
another 10 years. They are surprisingly complex for the size (and
age) with
about 20 ICs and are very well put together. Comparing one of these to
a Sencore Cricket would be like comparing a 707 to a Cessna. Does
both in-circuit
go/no-go and out-of-circuit parametric (and Si/Ge). What's so
great about
them? They self-permute
their lead arrangement (and the PNP/NPN selection). No
switches to turn or buttons to push. So you just poke at the
transistor and if it beeps it's good (it identifies the pinning and
type on LEDs). The is an important feature when your computer
has several thousand transistors. Downsides, well, these are very
old. They don't contain anything unusual, the schematic is
available, but they are OLD. Also the test leads are unusual in
that they aren't banana ended, they have a 3-pin comb you stick into
the transistor socket. So
if you get a used one check that it comes with leads or you'll need to
make a set. The Leader transistor test clips (the banana jack
versions) and probe became an almost industry standard and are what
come with the Vu-Data above (and are probably the right ones for the
B&K). The 906A is a horizontal layout of the 906 with the
same functionality but newer. They removed the E&C indicating LEDs
(superfluous, they are just the inverse of the B LED) and it has easier
access to the battery.
Capacitor testing
Used mostly to look for bad
electrolytics. Since 98% is checking
in-circuit capacitors for ESR a standalone ESR meter is probably the
most useful tool. For very large caps that you can disconnect and
measure
you are also interested in leakage. Capacitor values
rarely
change, a
"capacitor meter"
is useless as a test tool.
Avoid: Capacitor meters, radio cap
testers, Vintage
Eico/Sprague/Paco/Heathkit
testers, units with magic-eye or tuning-eye tubes, anything built into
a DMM or LCR meters & bridges.
Sencore Z-meters
Any of the Sencore Z-meters such
as the LC53, LC75, LC77,
LC101, LC102 (pictured) or LC103
would all be good choices for large electrolytics that you can isolate,
used LC53 & LC75's are routinely on Ebay
for under $200. The lower
end are out-of-circuit only. As you progress in price
some have the ability to measure ESR, some ESR in-circuit and then
in-circuit capacitance as well as ESR. I'd say you'd virtually
never need a tester like this for digital board repair, only analog,
power supplies
& motor run caps. Some of these have ringers which are good
for SMPS and monitor repair.
Almost any Standalone ESR meter
Measures the most common failure
mode of capacitors. Hands-free and a beeper are nice features to
have.
In-circuit is a
requirement, you want one with a very low p-p output voltage (<20mV)
and you'd like something at least a little electrically rugged (or
repairable) so it
doesn't blow up when you accidentally hook it up to a charged
cap. I use a CapAnalyzer
88A
most of the
time (on modern stuff), it also does a DCR (short)
test, but the probes are really designed for small chip caps.
My next purchase is going to be a Capacitor
Wizard with the protection
kit. Along with the more convenient leads, these are 5mv,
high-accuracy (log analog meter) 100khz testers and they have a beeper
which is handy. You can use some ESR meters as a sort of
continuity/leakeeker-like device for finding shorts. Also see Anatek's
Comparison of ESR Meters.
Tenma ESR meter
Another of my favorites is
the Tenma
ESR
meter (discontinued, but routinely on ebay for about $50) low
accuracy & only 50KHz but almost
indestructible, in fact some people use it on live
circuits, great for the big filter caps that I'd be afraid of
subjecting the 88A's
auto-discharge
to. People seem to unfairly rag on this tester, but it's the one
I grab
first for poking at unknown electrolytics in power supplies.
There is a failure mode you should be aware of, it you are going to be
dropping it or slamming it around the DC blocking capacitor on the
input is so big and heavy that it can break the solder lands it's
attached to. It's easy to insert a big glob of hot glue under it
to prevent this. I'd suggest replacing the supplied test leads
immediately with some nice (non-plated) ones. A drop of DeOxit in
the banana jacks wouldn't hurt either. From looking at the
circuit I'd say the Tenma is a
cheap clone of the original Creative Electronics ESR meter (which was a
well-regarded tester).
Wire Wrapping
Wire
Manual wrap/unwrap tools
Electric wrapping tools
Standard Pneumatic is what you are looking for, but I have used the
Gardner Denver with good results.
Avoid: Hobby brands or
battery powered units.
Cut, Strip & Wrap (CSW) bits
CSW
is the light sabre of wire wrapping. You stick the wire in,
put it over the terminal and zing it strips the insulation off, wraps
the connection and cuts the wire. The bits and sleeves are
individually serialized, precision matched and calibrated for exactly
one wire gauge and insulation. When using CSW bits you tether
your gun so it cannot hit the floor (not kidding). Bits &
sleeves can cost
$300
for the pair. You do not lend out CSW bits to even your oldest
and
most trusted friends. CSW wrapping is very dependent on the wire
insulation, you typically pick a special tefzel type, not just generic
wire wrap wire.
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