Understanding Un-Modules

Un-modules are simple devices that plug into the K2 in place of some options.  They are useful because the K2 has to be modified before installing most options.  In many cases these modifications cause the radio to no longer operate unless the options remain installed.  This is where the custom circuits on un-module option bypass headers come into play.  Installing the corresponding un-module device in place of an option sufficiently restores the radio back to its stock configuration so that it will function after an option has been removed.

Besides their integral role in our rework-free “Option Ready” K2 assembly method, there are many other situations where un-modules might come in handy …

1. If your K2 no longer works after you modify it for and install a new option, you can quickly isolate the fault down to either the option or your K2.  If the option is at fault then you can continue to use your radio while it’s being repaired.
2. If it takes longer than expected to modify an option, you can still use your radio without it until it is ready to reinstall.
3. While modifying your fully loaded K2, you might find it helpful or even necessary to remove some options.  (Such as removing the KSB2 when changing the value of RF-R98 per the “Power Control” app note / “ALC Modulation” fix.)
4. They permit signal tracing the portions of the K2’s circuit boards that are normally hidden under the options.  (Similarly, if you have the KDSP2 installed and you want to redo the 4 MHz oscillator calibration, you can remove it to access test-point 3 on the RF board.)
5. If you want to compare performance both with and without an option installed. (Just be sure to power off your K2 while doing the swapping.)
6. If your fully loaded K2 stops working altogether, un-modules will facilitate rapid board-level fault isolation.  If the fault is with an option then you can still use your radio while it’s being repaired.

Two option supplied connectors must be added to the RF board to support all of the options that mount on the top cover of the K2 enclosure.  In contrast, the preparations for adding all of the options that mount directly on its main circuit boards require the removal of 13 original parts from the K2’s circuit boards and the installation of 25 additional “option supplied” parts on them.  After these “option preparation” changes have been made, the radio will no longer function unless all of the circuit board mounted options remain installed.

The simple circuits on un-module option bypass headers provide an easy remedy to this situation.  Installing an un-module in place of its corresponding option restores the radio back to its “stock” electrical configuration, thereby enabling it to function after the option has been removed.  This is illustrated in the following color-coded diagram which shows the portions of the K2 schematics that relate to un-modules, and also shows the restoration circuitry on the headers themselves.

Twelve “un-module related” parts must be removed from the K2 while preparing to fully load it with options.  These parts include: two caps C6 & C167; three resistors R88, R89, & R90; and seven option bypass jumpers (A.K.A. zero-ohm resistors) W1, W2, W3, W5, W6, R18, & R19.  Five of these removed parts must be replaced, and in three cases their replacements are Single Inline Package (SIP) connectors.  The details of these five remove-and-replace (rework) changes are as follows:

• The original 470 Ω R88 on the RF board gets replaced with a 2.7 kΩ R88.
• R89 on the RF board gets replaced by jumper wire W89.
• C6 on the bottom of the RF board gets replaced by K60XV mating connector J15 (60 Meters) on the top of the board.
• Zero-ohm resistors (jumper wires) R18 & R19 on the bottom of the Control board are both removed to make way for the installation of KAF2/KDSP2 mating connectors J1 (Audio Filter In) & J2 (Audio Filter Out) on the top of the board.

Replacing components (and jumper wires) with mating connectors for the options requires the utmost care when removing the original parts.  Otherwise, the connectors might not sit perfectly flush and square on the reworked circuit board.  Even if they do, the resulting installation still might not remain mechanically sound and function reliably for the life of the radio.  Concern about the reliability impact of this PCB rework is what motivated us to develop and promote the alternate K2 assembly method described in our Rework Eliminator™ Companion Guide.  This assembly method lets you build the K2 and then fully load it with options without ever doing any PCB rework during the process.  In fact, once the base K2 has been assembled, it can be fully populated with options without any additional soldering on its circuit boards.  (Un-modules play a crucial role in making this possible.)

Fully loading a K2 with options requires the installation of many more “option supplied” parts beyond those shown in the above diagram.  These “other” parts aren’t mentioned because they don’t require “un-doing” for the K2 to operate after their associated options are removed.  Interested readers will find all 40 “option preparation” changes (two+13+25=40) on the annotated K2 schematics in Appendix B of our Rework Eliminator™ Companion Guides. 

Un-modules enable the K2 to operate after their associated options have been removed.  Their circuitry restores the K2 back to its “stock” electrical configuration, as it was prior to having been modified for the option.  Un-modules also simplify installation of the necessary devices so that they can be installed without referring to the K2 schematics.

Thus, although some jumper wires and caps are all that you supposedly need to replace most options … the fact that you must know where to install them, plus the fact that despite knowing this you still could insert them in the wrong place … means that discrete parts are not un-modules.

The KSB2, KNB2, and K160RX options add desirable features to the K2.  However, once they’ve been installed there’s no easy way to temporarily remove them.  Prior to their installation, one or more bypass jumper wires must be removed from the RF board.  In addition, for some options a few other components must also be removed or replaced.  Because of these changes, you can’t just unplug these options because the radio won’t operate without them.

Until now, the commonly accepted method of removing an option has been to undo the changes that were made to the RF board when the option was first installed.  That might be an acceptable solution if you are permanently removing it, but what if you only want to take one out temporarily for any of the following reasons?

• To modify it
• For high-level fault isolation (in case the radio stops working altogether)
• For signal tracing parts of the RF board that are otherwise hidden by the option
• To minimize power consumption when battery power is limited

Enter the Un-Modules!  By using these simple and easy-to-build devices, you can quickly remove their associated options without modifying your K2!  You’ll note that Un-Modules aren’t exactly the same as removing an option by the traditional K2 PCB rework method since the resulting signal paths will be a little longer.  Thus, signal leakage and stray inductance and/or capacitance may be slightly higher.  Even so, with proper construction practices they still ought to be better than with the actual options installed, so the impact of Un-Modules is probably negligible.  More importantly, by using Un-Modules you’ll be sparing your RF board from repeated PCB rework and the very real possibility of serious damage as a result!  In summary, the benefits of Un-Modules … 1) they make it really easy to remove the options and 2) they eliminate the chance of damaging your K2 … should outweigh any concerns about their possible negligible impact on performance.

What you’ll need.  Foremost, you need the proper Single Inline Package (SIP) terminal strip connectors.  They should have 230 mil (.230") gold-plated mating posts since the K2 has gold-plated sockets, but tin plating is actually preferable for the solder-tails.  The exact length of the solder-tails isn’t critical; somewhere around 120 mils (.120") should work fine.  You can either buy individual connectors with the required number of pins, or just get one long strip and cut it up to create the lengths you need.  You want connectors with a single row of pins spaced 100 mils (.100") apart.  Slightly “smaller” metric headers also exist with pins that are 2 mm apart; you don’t want those!  Also, don’t get connectors that are designed to be easily broken apart because they are too flimsy and the longer headers would likely break apart under the forces of insertion and removal!

The other parts you’ll need are a 560 ohm ¼ W resistor and replacements for most of the parts you removed from the RF board when you first installed the options.  Don’t try to reuse the original K2 parts because their leads won’t be long enough!  You will also need the following tools and supplies: a soldering iron and solder, some insulated or bare hookup wire, diagonal cutters, needle-nose pliers, a small vise, and some brightly-colored quick-drying paint.  Don’t use spray paint because it might contaminate the connector contacts!  I used orange nail polish leftover from Halloween.

1. Solder all components and jumper wires to the connector tails, never to the posts!  If you are unable to determine the difference … the posts must be gold-plated while the tails should be tin-plated and noticeably shorter than the posts.
2. Never insert or remove an option or an Un-Module while the radio is powered on.
3. I haven’t created an Un-Module device for the KAF2 option because I don‘t have one in my K2.  Such an Un-Module would need to span two connectors in the K2 making it more involved mechanically than the simple devices I have constructed.

The SSB Adaptor option can be replaced by the trio of simple Un-KSB2 headers shown above.  When properly installed, they duplicate W2, W3, and C167 which you removed from the RF board before installing the KSB2.

• 2   3-pin .100" SIP terminal strip connector
• 1   12-pin .100" SIP terminal strip connector
• 1   .001 µF ceramic capacitor

1. Using quick drying paint, mark pin 1 on one end of the 12-pin connector.
2. While the paint on the long connector is drying, solder a jumper wire between pins 1 and 3 of both 3-pin connectors.  (Since they are symmetrical there’s no reason to mark them.)
3. After it has dried, solder the capacitor between pins 7 and 12 of the 12-pin connector.

Remove the SSB Adaptor and plug in the 12-pin Un-KSB2 header at J11.  As shown in the silkscreen on the RF board, pin 1 goes toward the left side of the radio when it’s viewed from the front.  Also plug in the two 3-pin Un-KSB2 headers at J9 and J10.  They are near the right edge of where the KSB2 mounts on the RF board.  ALWAYS INSTALL ALL THREE UN-KSB2 HEADERS (AS A SET) WHILE THE ACTUAL KSB2 OPTION IS REMOVED FROM YOUR K2!

The Noise Blanker option can be replaced by the clever Un-KNB2 header shown above.  In conjunction with the installation of an option supplied alternate value for RF-R88 in the K2, its circuitry duplicates the attenuator that was originally formed by the three resistors you removed before installing the KNB2.

• 1   8-pin .100" SIP terminal strip connector
• 1   100 Ω ¼ W resistor
• 1   470 Ω ¼ W resistor
• 1   560 Ω ¼ W resistor

1. Using quick drying paint, mark pin 1 on one end of the connector and wait for it to dry.
2. When installing the resistors in the next step, position them either “above” or “behind” the connector relative to the image above.  This is important because there’s very little clearance between J12 on the RF board and the densely populated KSB2 module (when it’s installed).  If the resistors extend even slightly beyond the “front” edge of the connector, then their leads might touch component leads on the KSB2!
3. In this step, install the three resistors by forming their leads around the tails of the connector pins but don’t solder them yet:
   1. The 470 ohm resistor goes between pins 1 and 2.
   2. The 560 ohm resistor goes between pins 5 and 6.
   3. The 100 ohm resistor goes between pins 1 and 6.
4. Now solder the resistor leads.

Remove the Noise Blanker and plug in the Un-KNB2 header at J12.  As shown in the silkscreen on the RF board, pin 1 goes toward the left side of the radio when it’s viewed from the front.

There are no issues regarding the use of this Un-Module.

The 160 Meter & Receive Antenna Switch option can be replaced by the simple Un-K160RX header shown above.  It duplicates jumper wire W1 (RX Antenna Bypass) which you removed from the RF board before installing the K160RX.  I haven’t actually tested this Un-Module but I’m confident it will work.

• 1   16-pin .100" SIP terminal strip connector

1. Using quick drying paint, mark pin 1 on one end of the 16-pin connector and wait for it to dry.
2. After the connector has dried, solder a jumper wire between pins 1 and 7.  WARNING!  IF YOU LOOK AT THE SILKSCREEN ON THE RF BOARD YOU MIGHT BE MISLED TO THINK THAT THE JUMPER SHOULD GO BETWEEN PINS 1 AND 6, BUT IT SHOULD NOT!  YOU CAN CONFIRM THAT IT GOES BETWEEN PINS 1 AND 7 BY REFERRING TO THE K2 SCHEMATICS.

Installing the Un-K160RX is more involved than the other Un-Modules because the K160RX is hard-wired to the rear-panel RX Antenna jack, making it difficult to remove.  Also, note that there’s no pin-1 indicator in the silkscreen artwork for J14.  Pin 1 goes toward the left side of the radio when it’s viewed from the front.