Gary's top ten list of kit failures
(By Gary Surrency, AB7MY support@elecraft.com , with apologies to David Letterman)
Hello K2 aficionados,
I thought it might be a good time to present the 10 most common reasons for kit failures that I have seen during recent repairs.
Hopefully, this information will improve your kit building experience, and possibly save us some support calls and returned kits for repair. ;-)
So, without further ado, here are the most common kit problems we've seen, starting with reason number 10:
10. Bad or faulty components.
There is seldom a defective component responsible for kit failure. It happens, but not that often. This is sometime difficult to determine as a
result, since we tend to not suspect a bad part even when it *is* the cause. Voltage, resistance, and diode or transistor junction tests can
often reveal which part is at fault.
9. Missing components.
Yes, we do sometimes make mistakes and omit a part or two. You can reduce the delay time required for us to ship out missing parts to you by first
taking a complete inventory when you receive the kit. Often we will be able to ship any missing parts out to you before you get to the step
where the parts are called for in the assembly instructions. Let us know quickly, and we will ship missing parts to you pronto!
8. Failure to observe instructions, or read the manual / errata sheets.
Wayne and Eric (with the help of many people on the Field Test team) have written a very good manual, reminiscent of the old Heath manual. Some say
our manuals are even better than those that Heath did. Nevertheless, it does no good to write these instructions if you choose not to follow
them. Be sure to observe any last minute addendums to the manuals that are sometimes included after the initial printing was done. An example
would be the firmware upgrade sheets, and any clarifications or changes to components that sometimes are made to improve the products. Please
read carefully before, during, and after building the kits. Often, you will notice something you overlooked the first or second time through the
instructions.
7. Failure to observe the proper calibration or alignment procedures.
Yes, you must align the kit properly or it will not work well. An example would be during the K2 band-pass filter alignments. *Always* use a 50 ohm
dummy load and a QRP watt meter if you have one. And DO NOT try to align the BPF at 5-10 watts!!! Yoy will get a much better peak indication if
you keep the Power level under 1-2 watts. I use the 1 watt position on my OHR WM-2 watt meter when I perform these alignments, since it keep the
power level on the PA's low to minimize heating, and more importantly - it just produces a sharper indication as the inductors or trimmers are
adjusted. For CAL FIL, if you set the IF filters to the recommended starting values shown in the manuals, you will be close to proper
adjustment. But you will not get the full performance out of the K2 unless you spend some time finding the best BFO values for your
particular radio. Using Spectrogram is probably the best and easiest method to run CAL FIL. But even with it, you may need to familiarize
yourself with the procedure a few times before you get the process down pat. Once down, be sure to write down the settings so you don't have to
start from scratch again should something happen, like a full reset.
6. Incorrect wiring.
Fortunately, there is very little wiring in the K2 and its accessories (the ATU has two cable assemblies). But it is still possible to connect
the wrong wires to the connectors. We've seen this most frequently with the Freq. Counter probe, and speaker wiring. The Freq. Counter won't work
at all if you connect the inner conductor of the RG-174 to the ground pin! Observe the diagrams carefully and you won't have any trouble. If
the audio output is low, chances are, you reversed the wires on either the plug that goes into the RF PCB, or you wired the external speaker
jack wrong and have the "hot" side of the audio output grounded. These two problems are fairly common.
I'll add counting the turns to the toroids under this same heading, as there has been some of that too.
Count the toroid windings at least two or three times before assuming they are correct. On the new ATU, be sure to get the correct wires into
the correct connector pin locations. The crimp pins used for this are small, so be careful and use minimal solder and heat during assembly. The
best way to attach the crimp pins, is to use the correct crimping tool. I had good success using the inexpensive crimp tool Radio Shack sells,
pn. 64-410, $7.99. Although it is specified for phone connectors (the small lug type), it does a good job on the small pins used in the ATU
wiring assemblies. Just use care, and trim the wire ends appropriately and evenly. We include a few spare crimp pins in case you make a mistake.
5. Reverse installation of components.
These errors are hard to find sometimes. Any diode that is in backwards is certainly not going to work very well. And the funny-looking MOSFET
device at Q2 in the T-R switch is easy to install backwards (it goes with the silver side toward the Front Panel). But there have even been
transistors and varactors installed backwards, so be careful and observe the silk-screen on the PCB and follow the manual directions carefully.
4. Mis-identified components.
The tiny little labeling on the monolithic caps is hard to read, and the labeling when you *can* read it is confusing sometimes. An example would
be the three-digit code to identify the capacitance value. Don't confuse a cap marked 47J (47pf) for 471 (470pf). Use a magnifier if necessary,
and double check the parts list if you aren't sure. A capacitance meter is helpful, or an ohmmeter for the resistors if you haven't learned the
resistor color code yet.
3. Don't get in a hurry, or work late.
It is not a race to build these kits!!! If you rush through the building process, you will be several times more likely to make mistakes. Who
cares how long it takes to build these kits? The important thing is to do it right, and take your time. If you rush through the construction,
you'll just find yourself with nothing left to build and then you'll get "builder's withdrawal. The only cure for this, is another kit! (this is
to our advantage, however!). Savor the building experience, since it can be a relaxing time and is good therapy and cheaper than psychoanalysis.
Work a little while at a time. Take frequent breaks, get up and walk
around for a short time, or do something unrelated for a while. Use a good light and/or magnifier lamp. Clear off the bench, and use lots of
small containers or cups to hold the parts so they are handy and don't get lost or mixed up. Examine the working position, and if the bench is
too high or too low, adjust your seat height or the bench height. Don't bend over too far and get a neck ache or back ache. Build very slowly and
carefully, so that you will be pleased to show your workmanship to someone else, and you won't have to go back and do something over again.
It is better in the long run to work slowly, take lots of breaks, and double or triple check each step. I never install more than one component
at a time, for example. And I take pains to be sure each and every component is carefully installed flush on the PCB, and I do not bend the
leads to hold them in place. That makes it much more difficult to remove parts if you need to for any reason. Use a "third hand" helper if you
need to, or get the proper bench tools or PCB vise to make it easier.
2. Use the correct solder and proper soldering technique.
Although the manual recommends a low-residue flux solder, I do not particularly like them. To me, there just doesn't seem to be enough flux
to wet the connections and make a pretty joint. I use Kester 44, SN63/PB37, 0.020" diameter solder. Any solder with small silver content
is also good, but buy the smaller diameter solder, since it is much easier to control the amount of solder you melt off into the connection.
The large diameter solder just puts too much solder into the connection, and takes more heat to melt. It is *not* necessary to fill the
through-plated holes with solder to the point where there is a big blob of solder above the connection. Use the least amount of solder necessary
to make a good connection. Try to make a connection that has a fillet shape to it, or a flat meniscus (look it up) shape. It will be easier to
clip the component leads if less solder is used, and the lead lengths above the PCB will be less. This is especially important on the upcoming
ATU PCB's, since many of the leads must be flush cut to prevent shorting to other components. If you use the minimal amount of solder, this will
be much easier to accomplish. Always use the correct temperature iron too.
I like to solder at 600-650 degrees F, and desolder at 700 degrees F. If
your iron is not temperature adjustable, or is very old, treat yourself to a new one. I like the Soloman soldering stations, available from
Circuit Specialists for $56 to $86. You can see them and order from
http://www.cir.com. Other stations, such as the ones from Weller and Edsyn are good too, but always be sure to use the correct size tip and
heat for the job.
Also, using excessive amounts of solder may result in solder splashes or bridged PCB pads. Resist the tendency to apply more solder, and strive to
make each connection look like it was "wave soldered", as commercially produced PCB's are. Practice, practice, practice.
If you don't have one already, get a solder sucker to assist in removing parts that you might place in the wrong place. I have two - one for the
big jobs and where access is not a problem. And another smaller one for tight places and delicate work. Clean them often so they have full vacuum
and do not shed removed solder all over the workbench or your carpet. ;-) Desoldering braid may be used after the solder sucker has done its work,
to restore the PCB pads to like-new condition. When finished with the rework, use a cotton swab moistened with acetone or denatured alcohol to
clean off any excess flux that may attract dirt or moisture.
On all of the components that are installed underneath the PCB:
First pre-trim the lead lengths of each part so that there is no excessive lead protruding on the top side. You can do this by just
holding the part near the edge of the PCB and clipping any portion that extends more than the PCB thickness. Or, find a PCB hole near the edge
and insert the component lead momentarily in it so you can gauge how much to clip off. When installing the parts on the PCB bottom, *always* solder
it from the bottom where practical, and use minimal soldering dwell time to complete the connection. It is not necessary to solder the
bottom-mounted parts from the top side, as this may be difficult to do because of previously mounted, nearby parts. Once you've done it this way
a few times, you'll find it much easier and there will not be any need to try and clip off the leads on the top of the PCB where nearby parts may
interfere with your wire cutters.
Do not apply excessive force to the leads of the monolithic caps, or the molded RF chokes! Gently form the leads to fit the PCB holes, and do not
twist the RFC leads or fracture the epoxy coating on the RFC's or mono caps. It is OK to break off some of the ceramic coating on the disc
capacitors if it extends too far down the leads. Use your wire cutters or needle nose pliers to break it away, then rotate the tool on the leads to
get any remain ceramic coating that may interfere with soldering. Watch out for the tiny 3.3pf and 4.7pf coupling caps, as they are very small
and fragile and will break easily. Hold the lead near the cap's body with a small pair of pliers, and then bend the other end until it fits the PCB
pad hole spacing. Do not force any of the components into the PCB if they do not insert easily. Instead, remove them and inspect the cause of the
interference, and adjust the lead spacing until the part inserts easily.
AND THE NUMBER ONE PROBLEM IN KIT BUILDING IS....................
1. Improperly tinned toroid leads.
This is the winner (or loser, depending on your point of view) or all kit building problems. Learn how to do it correctly, and *DO NOT* install a
toroid with poorly tinned leads. I like to use a soldering iron tip of about 680-700 degrees F, and I hold it against the enamel wire for about
5 seconds to melt the insulation and begin the tinning process. A little extra solder helps to conduct the heat to the wire, and the extra flux
helps remove the oxides and adds fresh solder to the copper wire. Clip the wires to about 1/2" after completing the winding process, and pull
them tight against the toroid core. Start as close as you can to the toroid, and move the iron toward the end of the lead as you add solder
and see the enamel melt away. If you do it just right, there will be a little ball of melted enamel pushed toward the end of the wire. Check all
around the wire to be sure there is complete coverage, and add solder and tin any place that is not bright and shiny with solder. If you do not tin
the wire very close to the toroid, chances are you will pull an un-tinned portion of the enameled wire into the PCB pad during installation and
have difficulty making a good connection. Merely applying more heat and solder will not correct a poor tinning job, so do it correctly before you
install the toroid. You will spend much less time in the long run, and the connections will be good and not the #1 cause of kit failures we have
seen on returned kits.
Do not rely on sandpaper to remove the enamel, and them hoping the soldering operation will tin the lead! In almost all cases, this does not
work. Scraping, sandpaper, and burning off the enamel with a match or lighter just does not work as well as using the method described above.
Chemical insulation removers are hazardous, messy and they may spill on your bench or clothes. Industry uses mechanical enameled wire removers or
heated solder pots, but they are expensive for home use. Practice tinning the wires using a hot iron and you'll do just fine.
Above all, have fun and use care when building the kits. And when you are
finished - they will actually work!!! ;-)
Be sure to check our web page for recent announcements and Builder's Notes, etc.
http://www.elecraft.com
Thanks for making Elecraft a big success. We want you to succeed too!