Up until this point, both generations of K5BCQ's printed circuit boards are treated the same. The third generation kit boards had positions that allowed C50 and C63 to be mounted on the new printed circuit board instead of "tombstoning" them (standing them on end and wiring to the projecting end) on the main board. Second generation did not have that feature so we need to tombstone those two capacitors.
With all ten parts mounted on the board it is time to prepare the µBITX board for the kit.
Now to re-arrange the preamp power:
Referring to the sketches, locate the receive (RX) power supply trace shown in the main sketch and carefully separate it at the location shown in the expanded sketch of the area (Figure RX). Use a sharp knife to cut across trace. Make a small gap, just enough to ensure that it is open. Carefully scrape the conformal coating from each end of that severed trace to reveal the bare copper conductor. The end that sourced the original receive voltage will be jumpered to the “RX” input on the kit board.
Scrape off the coating over the 12 volt supply trace section adjacent to the other end of the severed trace, the one that leads to R52. Use a small wire clipping to connect the two. This taps the full-time 12 volt supply to R52 and the rest of the receive preamp, keeping it active.
Refer to the sketches and find the transmit (TX) supply trace to R66. I like to take advantage of the through-hole vias that connect to the bottom layer. They make excellent connection points. Cut the TX trace below the “knee” near the short 12 volt supply run. Remove the coating on the end of the severed trace that feeds R66, and around the adjacent 12 volt via. Solder a short wire clipping from the via to the bared trace to R66. If you bend one end of the clipping 90 degrees then it will drop into the via to help hold it in place. Clean the via on the remaining TX trace for connection to the “TX” input to the kit board.
Locate capacitor C50 shown in Figure i/o. Desolder it and gently remove it. Stand it on end on the pad leading to R50 and solder it in place. The exposed end of this capacitor will be where the receive pre-amplifier will be connected from the "C50" pad on the new kit board.
Locate capacitor C63 nearby, remove it, and solder it on end to the pad leading to R65. The exposed end will be where the microphone pre-amplifier will feed the new kit board at the "C63" point.
I will leave the option of using plugs and jacks to the individual. I prefer just hard wiring to keep things simple and avoid intermittent connections and to save space. At this point you can install the supplied header pins or just the six jumper wires to the board. Clean off any flux with alcohol or flux remover.
That is a lot of connections for that little board! Looks like a 6-legged spider. I positioned mine with the bottom of the board up next to C52 and C64, those big electrolytics.
That completes installation. Be sure to check your work before applying power. I have not had any issues with my installations and cannot think of any trouble shooting hints. If you find that something doesn’t work, you might start with voltage checks at the RX, TX, and 12 volt points. An oscilloscope would be the best tool to follow the signal through the gating. Without an oscilloscope I would suggest a signal injector like this example.
I hope that you will enjoy the results of this modification as much as I have. If this is your first venture into the world of surface mount electronics I am sure that you will have picked up some considerable skills, too. Perhaps you will be a bit more comfortable working with these tiny parts and are ready to tackle some more of these projects!
de ND6T