bwc@ganehd.UUCP (Brantley Coile) (05/02/85)
I want to build some one-of-a-kind stuff to try out ideas on parallel systems. My first question is how should I fabricate the equipment. While this may be an easy question to answer for production design, it is not so easy for a OOAK system. My choices are: 1) wire wrap 2) make a pc board I don't like (2) because of the cost and effort. Doing the artwork and having made sounds time consuming and expensive. It does give me very reliable stuff. It also make debugging impossible. I don't like (1) because of reliability. I understand that as wire wrap ages it develops the flakies. This leaves me with - 3) point to point I could do (3) if I used a solderless circuit board to prototype and do point to point when the board was debugged. This led me to another problem; I would need one heck of a solderless circuit board to debug stuff. Why? Why do boards have to be so big? If I were going to build a million of them I could see the benefit of reduced chip count that could come from a large board. I assume that there could also be a lot of savings in other things with a larger board size. But I don't care about any of them. If system design is similar for hardware as software, the smaller, functional boards would be better. I am not saying that the boards should be interfaced with some bus definition like STD, S-100, MultiBus, etc. Each board would be more of a module than a board, each with inputs and output. If I did this I could debug them one the solderless circuit board and when working make the point- to-point board. Well, what do you think. As you might have guessed I'm not a hardware engineer although I have built a small micro. Please send me you thoughts on the matter. -- Brantley Coile CCP ..!akgua!ganehd!bwc Northeast Health District, Athens, Ga
BillW@SU-SCORE.ARPA (William Chops Westfield) (05/07/85)
Go wire wrap. I don't know where you heard tha wire wrap get unreliable as it ages, but I dont think that is true. From most indications, a wire wrap connection is as reliable as a soldered connection (the possible exception being in a high vibration environment). If you expect the prototype to last 50 years, aging might get you... At Stanford we have designed and built quite a bit of hardware, and it all gets wirewrapped first (that way you get to correct the mistakes a lot more easilly too). Designing a circuit board for any but the simplest circuit is both difficult and very expensive. Using sockets on the board would probably lower the reliabilty to that of wire-wrap (hmm - thats probably where the aging question came in - things in sockets (wire wrap or solder tail) tend to be less reliable than tyhings that are directly soldered to. BillW
karsh@geowhiz.UUCP (Bruce Karsh) (05/08/85)
> > I want to build some one-of-a-kind stuff to try out ideas on > parallel systems. My first question is how should I > fabricate the equipment. While this may be an easy question > to answer for production design, it is not so easy for a > OOAK system. > > My choices are: > > 1) wire wrap > > 2) make a pc board > > I don't like (1) because of reliability. I understand that > as wire wrap ages it develops the flakies. I disagree. Wirewrap is more reliable than hand soldered pc boards. We have instruments which we use in our field operations that have both pc and wirewrap boards in them. These boards are subject to a lot of vibration and temperature cycling. The wirewrap boards are much better than the pc boards. The wirewrap boards are also more dense than the pc boards. The reason that wirewrap is so reliable is that: 1) The wire is held under tension against the post. That keeps it from falling off due to thermal expansion/ contraction. 2) The corners of the posts are sharp and form an airtight connection with the wire. 3) Since there are 4 corners on each wirewrap post, and about 8 wraps, there are 32 connections per post. Thats a awful lot of redundancy. It is very unlikely to fail. For one of a kind projects and small production runs, wirewrap is hard to beat. A good reference is a publication called Wire-Wrap from The Cooper Groop, PO Box 728 APex NC 27502. (919)362-7510. Catalog No. 55548. This goes into the materials science aspects of wire wrap. Of course, if you don't do the wraps properly, it won't work. But it's pretty easy to do right, and a proper wrap has about 100,000 lbs/sq in of contact force. Wire wrap is covered under mil-spec MIL-STD 1130. -- Bruce Karsh | U. Wisc. Dept. Geology and Geophysics | 1215 W Dayton, Madison, WI 53706 | This space for rent. (608) 262-1697 | {ihnp4,seismo}!uwvax!geowhiz!karsh |
luscher@nic_vax.UUCP (05/08/85)
> > I want to build some one-of-a-kind stuff to try out ideas. > How should I fabricate the equipment? > > My choices are: > 1) wire wrap > 2) make a pc board > 3) point to point (solderless breadboard) > My additional choices are: 4) point to point, directly soldering wires to either IC legs (tacky but cuts down cost), or to sockets. 5) insulation displacement I have used #4 at home and when soldering to ICs or sockets I find it a nuisance to add a wire withour having a previously connected one pop off occasionally. Otherwise this is quick, dirty, cheap and works. I have used #5 at work, and am preparing to use it at home (S100 board with insulation displacement sockets from 3M, bought as a kit some time ago). These are *EXPENSIVE* (I'm cheap?) but I found them VERY easy and *QUICK* to set up and change, a valuable advantage for OOAK equipment designed for fooling around and cut-and-paste design. They can be damaged however if wires are pulled out of the bifurcated terminals towards the side instead of straight up. If this happens the terminals spread and the next wire into that terminal will not be gripped tightly enough. Also don't pull wires too tightly around corners on any method at they tend to short through insulation (very difficult to find!). GOOD LUCK! -- Jim Luscher / Nicolet Instruments / Oscilloscope Div. 5225 Verona Rd Bldg-2 / Madison Wi 53711 USA / 608/271-3333x2274
ron@brl-tgr.ARPA (Ron Natalie <ron>) (05/09/85)
> My choices are: > > 1) wire wrap > > 2) make a pc board > > I don't like (1) because of reliability. I understand that > as wire wrap ages it develops the flakies. > SCOCTHFLEX is nice. It's expensive, but cheaper than making PC boards for prototypes.
binder@dosadi.DEC (Wherever you go, there you are.) (05/09/85)
I second the motion for wire wrap, very loudly, with one caveat: if your
hardware will include any extremely sensitive analogue stuff, eg the National
Semi DP8460 disk data separator, then you have to PC that area - Radio Shack
PC kits work fine, if you're careful.
I used to work for ModComp, and until 1978 virtually all ModComp hardware was
wire-wrapped. Done properly, wrap is as reliable as any other technology, and
it is, as was pointed out, a lot easier to fix. If you're serious about being
able to fix things, don't use a slit-n-wrap gun or any other tool that wraps a
continuous string. Instead, lay out your strings so that the second, fourth,
etc. wires in a string are wrapped at first level, next to the board, on both
ends, and the first, third, etc. wires are wrapped at second level. That way
you never have to remove more than three wires to add or remove any single
node in a string. During debug, you can connect new pins to an end of the
string, or you can cheat and go first-to-second in the middle of the string.
A comment on socket reliability is that sockets are also as reliable as might
be desired. BUT, and it's a big but, there are two kinds of sockets. One is
called a face-grip socket; it grips chip pins on the inside and outside faces,
which are wider, thus providing (it is claimed) more area of contact. The
other kind is called an edge-grip socket; it grips the pins on the edges
between pins. Face-grip sockets grip with less contact pressure, and the
advantage of the greater area is lost. Edge-grip sockets have a MUCH higher
clamping pressure, and they provide a good gas-tight seal between the socket
and the pin. FACE-GRIP SOCKETS ARE UNRELIABLE!!! EDGE-GRIP SOCKETS ARE VERY
RELIABLE!!!
Cheers,
Dick Binder (The Stainless Steel Rat)
UUCP: {decvax, allegra, ucbvax...}!decwrl!dec-rhea!dec-dosadi!binder
ARPA: binder%dosadi.DEC@decwrl.ARPAbright@dataio.UUCP (Walter Bright) (05/09/85)
In article <10460@brl-tgr.ARPA> BillW@SU-SCORE.ARPA (William Chops Westfield) writes: >Go wire wrap. I don't know where you heard tha wire wrap >get unreliable as it ages, but I dont think that is true. >From most indications, a wire wrap connection is as >reliable as a soldered connection. Wirewrap is as reliable as soldered connections provided: 1) A high torque wire wrap gun is used. 2) Good quality wirewrap sockets are used (the kind with square posts). 3) The full 1" of bare wire is wrapped around the pin. A good wire wrap connection will actually form a cold weld between the wire and the pin. You can tell this by unwrapping the wire. It should "tink" each time you pull it off one of the corners on the pin. A well wrapped board is immune to vibration. If you expect your circuit to last, do not used hand-held or battery operated wirewrap tools. They do not wrap the wire tightly enough, and I have seen many boards wrapped with them start becoming flaky after 3 to 5 years.
henry@utzoo.UUCP (Henry Spencer) (05/09/85)
Note also that if you are going to put things in sockets -- wire-wrap or
soldertail -- for heaven's sake break down and spend the money for good
(machined-pin, gold-contact) sockets. Worth every penny, just for the
absence of socket hassles.
--
Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!henryrbc@houxu.UUCP (R.CONNAGHAN) (05/11/85)
No one has mentioned Multiwire. Can be fabricated from schematics or a net list. Generally very fast turn-around compared to Printed Circuits. I have used most prototyping techniques, Wire-Wrap, Multiwire, PCB, and point to point. The favorite has gone from wire-wrap to Multiwire. A comment on wire-wrap robutness. It's not the wrapped connection reliability that causes problems. It't the intergratiy of the insulation. The insulation can often be nicked as it goes around a post. It can also were away if the board is flexed or moved alot. A wire-wrap system carefully built (automatically prefferred) and NOT MOVED or FLEXED much is a very reliable way to build. -- Robert Connaghan Microprocessor Group AT&T Bell Labs - Holmdel, N.J. houxu!rbc
jlw@ariel.UUCP (J.WOOD) (05/12/85)
For a short prototype run I like multi-wire. It's much more rugged than wirewrap, can be run off the wirewrap wiring list and component placement, and is multilayer; you can really pack it on the card. The components can be soldered on to the card, and changes can be made fairly easily. Joseph L. Wood, III AT&T Information Systems Laboratories, Holmdel (201) 834-3759 <ariel!>titania!jlw
jss@sjuvax.UUCP (J. Shapiro) (05/12/85)
Regardgin wire wrapping... > > 2) The corners of the posts are sharp and form an airtight > connection with the wire. > Nay - better than, this, the seal is basically a cold weld - damn unlikely that it will randomly remove itself. Things to beware of, however: At high speed, wire wrap temds to crap out. (i.e. > 8 Mhz or so). Then again, so do sockets. Beware of kinked wires - these *do* go with time, but are easy to spot once gone. In particular, the repair time given a known break is quite low. Also, get yourself an electric wire wrap gun - it will save many many hours of precious time, and will prevent a lot of bad wraps. I just completed a VAX I/O interface which was wirewrapped... I will be prototyping a small computer shortly using wirewrap. Jon Shapiro
caf@omen.UUCP (Chuck Forsberg WA7KGX) (05/13/85)
I recently developed a moderately large board (a laser printer controller with 1 MB ram, etc.) with the insulation displacement system. We had considerable trouble with the sockets coming apart after repeated insertions and withdrawl of the chips. As for my next project, I might use the method if the board was small, wasn't going to be used for very long, and I didn't expect to fuss with it too much before getting it to work. A prime advantage of the insulation displacement method is less board thickness compared to wirewrap. It's faster too, although a good stripper and/or prestripped wires make wirewrap much faster. With wirewrap, I find a manual tool ($5) better than the cheap electric types. -- Chuck Forsberg WA7KGX ..!tektronix!reed!omen!caf Omen Technology Inc 17505-V NW Sauvie IS RD Portland OR 97231 Voice: 503-621-3406 Modem: 503-621-3746 (Hit CR's for speed detect)
esco@ssc-vax.UUCP (Michael Esco) (05/14/85)
> Things to beware of, however: > > At high speed, wire wrap temds to crap out. > (i.e. > 8 Mhz or so). Then again, so do sockets. Not necessarily true. At NCR we used twisted pair wire wrap in a large, multiboard, 38-nanosecond processor. > Beware of kinked wires - these *do* go with time, but are easy > to spot once gone. In particular, the repair time given a known break > is quite low. > > Also, get yourself an electric wire wrap gun - it will save many many hours > of precious time, and will prevent a lot of bad wraps. > > Jon Shapiro Wire wrap is a perfectly good technique for limited-production devices. But it requires careful assembly with the proper tools. I'd venture to say that most complaints about wire wrap come from those who didn't put it together carefully or handled it roughly after assembly (No, you can't play frisbee with it). Michael Esco (formerly of) NCR E&M San Diego (but now at) Boeing Aerospace
b-davis@utah-cs.UUCP (Brad Davis) (05/16/85)
>> Things to beware of, however: >> >> At high speed, wire wrap temds to crap out. >> (i.e. > 8 Mhz or so). Then again, so do sockets. > >Not necessarily true. At NCR we used twisted pair wire wrap in a large, >multiboard, 38-nanosecond processor. > I once helped (did software) on a project that had 15 nanosecond signals running around on the board. The only twisted pairs ran off the board to a high resolution monitor. -- Brad Davis {ihnp4, decvax, seismo}!utah-cs!b-davis b-davis@utah-cs.ARPA
ron@brl-tgr.ARPA (Ron Natalie <ron>) (05/17/85)
> > >> Things to beware of, however: > >> > >> At high speed, wire wrap temds to crap out. > >> (i.e. > 8 Mhz or so). Then again, so do sockets. > > > >Not necessarily true. At NCR we used twisted pair wire wrap in a large, > >multiboard, 38-nanosecond processor. > > > I once helped (did software) on a project that had 15 nanosecond signals > running around on the board. The only twisted pairs ran off the board to > a high resolution monitor. > -- > The backplanes of the HEP, one of the worlds fastest computers with the worlds slowest I/O system are wire wrapped.
yrdbrd@bmcg.UUCP (Larry J. Huntley) (05/18/85)
In article <612@houxu.UUCP> rbc@houxu.UUCP (R.CONNAGHAN) writes: >No one has mentioned Multiwire. >Generally very fast turn-around compared to Printed Circuits. > >The favorite has gone from wire-wrap to Multiwire. > >A comment on wire-wrap robustness. >(etc.) > >Robert Connaghan >Microprocessor Group >AT&T Bell Labs - Holmdel, N.J. >houxu!rbc Although I can agree with Robert about Multiwire, I think that it is a little out of sync for the application the original poster had in mind (hobbyist or university lab "one-off" system, I think.) Multi- wire is great for something that you need 25 -- 1000 of. Computervision used the technique to build add-on boards in Data General computers, and they were at least as reliable as the multi-layer PCBs that were in the computers. It's a bit expensive for a single board, though. I have been using wire-wrap for 13 years now, and have never had any problems with well-planned, well-wrapped boards/systems. Some further comments: (1) The problems encountered with wire-wrap usually involve (1) the insulation failing where a wire passes around the corner of a socket/pin and cuts through the insulation, causing a short, or (2) a wire under so much tension that the inner conductor breaks (usually at the point where the wrap starts around the post) but the insulation stays intact, making the problem virtually impossible to find visually. (2) There are wire-wrap bits and sleeves which cut and strip the insulation as the wrap is being made. One of these pays for itself with the first board you build with more than 25 wires. (NO, this is NOT the "slit & wrap" tool discussed earlier. This is a genuine wire-wrap tool and it makes a proper 'modified' wrap on standard 0.025" sq. pins. If you need more information, let me know. I'll look it up.) (3) Be sure to use "levels" on your pins, and plan your physical layout to minimize wire lengths. Leveling the wires looks like this: Wiring Side | | | | | | <- pins |--------| |--------| |-------| <-- level 2 | | | | | | | |-----------| |---------| | <-- level 1 | | | | | | ------------------------------------------------------ <- board ------------------------------------------------------ | | | | | | | | | | | | <- sockets ------------ ------------ ----------- Component Side (4) Beware of stray inductance in wire-wrapped boards. If possible make your connections to power and ground with 20 ga. solid wire, soldered to busses on the board. If you must wrap the power leads, keep the wires as short as possible. A loop of 1" of 30 AWG wire can exhibit enough inductance to induce voltage spikes as high as 1 volt on the power leads of devices which are switching at 4 MHz. Wire-wrapping dynamic RAM arrays can be particularly exciting. Have great fun, 'brd -- Larry J. Huntley Burroughs -(B)- Corporation Advanced Systems Group MS-703 10850 Via Frontera San Diego, CA 92128 (619) 485-4544 -*- Non Circum Copulae -*-
kensmith@sunybcs.UUCP (Ken Smith) (05/20/85)
Well, since most of the net has seemed to suggest wire-wrapping you might like some pointers on how to go about it. First, make reasonable circuit schematics, and get a blueprint made. Using the blueprint start making connections using sockets and, for discrete parts get the pins that you insert into the board and solder the discretes onto later. (The only place these pins aren't necessary is when you have lots of resistors of the same value in generally the same area, in which case it is easier to just use another socket.) Keep going for as long as you can at one shot, this helps reduce the chances for errors. Keep a diagram that shows which parts are what (i.e. a layout diagram) so you can find them later. Labels also help (especially those labels for the back-side of sockets with the pin numbers, though these get expensive). Whether you start checking while constructing the circuit or after it is all connected is up to you, but do continuity checks on ALL connections, and (this is where the blue- print comes in) use one of those high-lighting markers to mark all the connections you have checked. The continuity checks are important, it's very possible to have breaks in the wires but the insulation is still intact so it LOOKS connected. A multi-meter that beeps for continuity checks is nice, as are clip probes and those headers you can stick in the socket that have pins on both sides. When done solder in the discretes and start to debug it... I'm still relatively new to wire-wrapping so there are probably many other things that make life easier that I haven't tripped over yet, but this should get anyone interested started on the right track. -- ----- Ken Smith - Don't rattle my bars!
arcorp@utcsri.UUCP (Alias Research Corporation) (05/20/85)
What is Scotchflex? Steve
brad@gcc-bill.ARPA (Brad Parker) (05/21/85)
In article <1143@sjuvax.UUCP> jss@sjuvax.UUCP (J. Shapiro) writes: >Regardgin wire wrapping... >> 2) The corners of the posts are sharp and form an airtight >> connection with the wire. This is known as "gas tight". >Things to beware of, however: > > At high speed, wire wrap temds to crap out. > (i.e. > 8 Mhz or so). Then again, so do sockets. This is not true. Get a good Augat board - worth every penny in noise reduction. Hell, people do ECL with these boards... > Beware of kinked wires - these *do* go with time, but are easy > to spot once gone. In particular, the repair time given a known break > is quite low. > >Also, get yourself an electric wire wrap gun - it will save many many hours >of precious time, and will prevent a lot of bad wraps. Of dubious use for small fixes (1-2 wire). Very handy for major jobs. -- J Bradford Parker uucp: seismo!harvard!gcc-bill!brad "She said you know how to spell AUDACIOUSLY? I could tell I was in love... You want to go to heaven? or would you rather not be saved?" - Lloyd Coal
roy@phri.UUCP (Roy Smith) (05/22/85)
> [...] but do continuity checks on ALL connections, and (this is where > the blueprint comes in) use one of those high-lighting markers to mark > all the connections you have checked. As someone who has fab'ed a few small-scale wire-wrap boards, I heartily agree -- If you don't ohm out EVERY connection, you are asking for trouble. Now, a question. I've gotten sick of those "Just Wrap" tools you can buy at Radio Schlock or through the catalogs. Either my technique is the pits (possible) or the tools just plain don't work right. I find that my percentage of good wraps is only about 2 out of 3. Every time I need to do another board, I debate shelling out the bucks for one of those OK electric jobs. Is it worth it? Any recommendations of pre-cut, pre-stripped vs. continuous feed wire? -- allegra!phri!roy (Roy Smith) System Administrator, Public Health Research Institute
esco@ssc-vax.UUCP (Michael Esco) (05/23/85)
> > Well, since most of the net has seemed to suggest wire-wrapping > you might like some pointers on how to go about it. First, make reasonable > circuit schematics, and get a blueprint made. Using the blueprint start > making connections using sockets... > Ken Smith For all but the simplist systems, I would strongly suggest you prepare a wire list. This could save quite a bit of time trying to debug a flakey circuit. Michael Esco Boeing Aerospace
kensmith@sunybcs.UUCP (Ken Smith) (05/28/85)
> Every time I need to do another board, I debate shelling out the > bucks for one of those OK electric jobs. Is it worth it? Any > recommendations of pre-cut, pre-stripped vs. continuous feed wire? > -- > allegra!phri!roy (Roy Smith) > System Administrator, Public Health Research Institute I've never used the "Just-Wrap" stuff, but the people I work for say it's definitely not for novices; experienced people may even have trouble. They loan me one of the battery-powered OK guns and that really saves my sanity! They are really nice compared to hand-wrappers. Considering the time saved they are definitely worth the $45 - $50 (Digikey or Jameco prices). I don't use pre-cut because the boards I've been doing don't follow very regular patterns. I'd consider pre-cut for memory boards or the like. I use those plastic spool holders with the stripper and cutter built in. Just be careful how you grab the wire when you go to strip it; it's easy to bend and (cringe) break the wire. I grip the wire with needle-nose pliers to strip it which seems to work well. Typically I don't have trouble with broken wire, just connections I missed... -- Ken Smith UUCP : ..![bbnca,decvax,dual,rocksanne,watmath]!sunybcs!kensmith
karsh@geowhiz.UUCP (Bruce Karsh) (05/29/85)
In article <765@ssc-vax.UUCP> esco@ssc-vax.UUCP (Michael Esco) writes: > >For all but the simplist systems, I would strongly suggest you prepare a >wire list. This could save quite a bit of time trying to debug a flakey >circuit. > Does anybody have a good wire list generator that they could post to net/mod.sources? If nobody has a good one, I have a minimal one that I could post if there is any interest. Bruce Karsh -- Bruce Karsh | U. Wisc. Dept. Geology and Geophysics | 1215 W Dayton, Madison, WI 53706 | This space for rent. (608) 262-1697 | {ihnp4,seismo}!uwvax!geowhiz!karsh |
hull@hao.UUCP (Howard Hull) (06/04/85)
In the cited article by Ken Smith, almost all of the technicalities with
respect to wire wrap have been expressed better than I could say them.
I would like to add, though, that use of a 110v powered hand wire-wrap gun
takes a little practice. I have found that there are two major disasters
that can happen:
1. If you press the gun too firmly down around the base of the post,
the wire will not feed properly, and (if you are lucky) the wire
will be broken after only one and a half turns. Given that (you
were unlucky) the wire was nicked, and that you didn't notice it,
it will fail later at it's own convenience, not yours. Be prepared
to do the wrap over, but keep in mind that the wire wrap system
depends on the posts remaining *square*, and that each attempt
puts little dents in the post that may compromise subsequent
attempts. Above all, WORK CAREFULLY. You may want to warm up
on a "junk" board before you start for real. For the bottom
wrap, press the gun all the way to the bottom of the post, and
then lift it about a millimeter off the board. Apply just enough
upward force to support the weight of the gun minus ~ .00001 oz
at that height while the trigger is pulled, allowing the gun to
rise slightly as the wrap proceeds (a major fraction of a second).
Whatever ya do, don't flinch. Inspect the wrap when you are done
to see that all the wire went on the post, and that the wrap is
even. This is a necessary, but not sufficient condition, so see
number 2., below.
2. If you suffered from linear withdrawal symptoms while doing the
wrap, and you thus lifted the gun slightly while wrapping, you will
have an even wrap, but nonetheless a *stretched* wrap. Since a
stretched wrap can be compressed (and thus result in a slightly
shorter wrap with an *expanded radius*) by pushing down on the
gun, if you want to have any hope of spotting a stretched wrap
you might have made, DO NOT press down on the gun as you are done
with a wrap! The result of pressing down is a floating wrap
(we call them "Weber Junctions" in honor of a certain technician
that did several hundred of them for us in a bit-slice micro we
put together some time ago). They are *very hard to detect* by
physical inspection, and may even pass electrical inspection until
the wire oxidizes. After that, kiss your sanity goodbye.
3. Always strip wire_wrap wire with a "gauged" stripping tool. Just
pulling the wire from the reel until it breaks, or use of a pair
of long-nosed pliers may stretch the wire, resulting in a tapered
gauge along the wrapped length. I don't know that this causes so
much trouble in the actual finished wrap as it does in the handling
of the wire by the tool while the wrap is being completed. It does,
however, contribute to failures as outlined in (1.) above.
Regards, Howard Hull
[If yet unproven concepts are outlawed in the range of discussion...
...Then only the deranged will discuss yet unproven concepts]
{ucbvax!hplabs | allegra!nbires | harpo!seismo } !hao!hullkeithe@tekgvs.UUCP (Keith Ericson) (06/06/85)
More on 110v wire-wrap guns: we bought a couple of (Gardner-Denver, I think) ww guns a few years ago, and had the same wire-breaking, bad connection, wire-stripping problems mentioned in the earlier article. Then our technician found someone selling *good* tips for the guns that make it virtually impossiblle to get a bad wrap or a broken wire, and it strips the insulation as it wraps! The bad news is that the tips cost as much (maybe more) than did the gun itself. But they've saved our sanity more than once, I' sure. Unfortunately I don't have the name of the source for the tips at hand; if you need the info get back to me and I'll try to find it (the technician left about a year ago and I'll have to find his paperwork, etc...) Keith Ericson at Tek Labs