Upgrade your Hitec Focus IIss to three channels

Upgrade your Hitec Focus IIss to three channels

McSwain, Alan

I’VE NEVER BEEN quite sure whether I should consider it a blessing or a curse, but I have always been one of those people who simply can’t own anything without taking it apart to see what’s inside to figure out what makes it “tick.” So, of course, it was business as usual when I recently bought one of the new Hitec* singlestick 2-channel radios from my local hobby dealer. As soon as the new radio hit the bench at home, out came the screwdrivers, and within minutes, I was rewarded with a pleasant surprise. This radio was originally designed to be a 3-channel system! All that was missing was a thimbleful of parts and a few minutes of soldering time. By bedtime that same day, I had completed the “upgrade” to my radio and I have been enjoying it ever since.

Warning: the modifications illustrated in this article, if performed on a unit still covered by the manufacturer’s warranty, will likely constitute suitable grounds for the warranty to be voided. Proceed with this modification at your own risk.

RECEIVER MODIFICATION

Modification of the receiver is quite easy because it involves only two parts and a little hobby-knife work. First, remove the receiver crystal from its recessed molding and set it aside. Now remove the polycarbonate plastic case from the receiver by lightly pressing inward on the two small tongue latches on the antenna-wire exit end of the case, one at a time, while you apply finger pressure to separate the case halves. A small jeweler’s screwdriver is an excellent tool for this task. Extract the printed-circuit board (pcb) from the lower case half by pulling firmly on the antenna wire. Set it down in front of you, solder side up, with the antenna wire to your left. In what is now the upper right-hand corner, locate the two, three-pin servo lead IDC headers. Just below these two, you will notice what seems to be an empty spot that’s just the right size for an additional header, but without any soldered pins protruding.

The unit is wave soldered, and the three holes that should be there may be covered by a thin layer of solder. To uncover the holes, simply use the tip of your soldering iron and brush the excess solder slightly to the side until the holes are revealed. Now install the three-pin IDC header on the component side of the board and solder one of the pins on the other side. Double-check that the pin is perpendicular to the circuit board before soldering the other two pins. Tin both ends of the 470pfd-chip capacitor and, referring to Diagram A, locate the position for the .0047mfd-chip capacitor, and solder it lightly, gently and quickly into place. Hint: the robotic assembly machine that these pcbs were assembled on was programmed to place two little red dots of epoxy straddling the position of every chip resistor and capacitor. When the Hitec engineers changed the design from three to two channels, they programmed the “pick-and-place” robot to skip the 470pfd-chip capacitor and the three-pin IDC header, but apparently, it wasn’t worth their time to reprogram the epoxydot program. So just find the two little, red epoxy dots, and that’s where your 470pfd-chip capacitor goes!

With the electronic mods completed and your hobby knife in hand, proceed to open a servo-plug hole in the upper half of the receiver case directly above the IDC header you just installed. Be sure to duplicate the exact shape of the other holes, or you will make it possible to plug a servo into your third channel backwards, and that could cause damage to both the servo and your receiver. Snap the circuit board back into its case and replace the crystal. You now own a 3-channel receiver!

TRANSMITTER MODIFICATION

Remove the transmitter crystal, the antenna, the battery hatch, the battery cassette and the four case screws. Place these parts in a Baggie or Dixie cup for safekeeping. Remove the transmitter case back and set it aside. The main transmitter pcb is held down with three screws; remove these and set them aside.

Using a Sharpie pen or similar indelible marker, label each of the four off-board connectors with a number, and write that number on the pcb surface next to the connector. Disconnect the four connectors and lift the pcb free of the case. Using Diagram B as a reference, solder the Kaynar jumper, the 22K-ohm chip resistor and the .01mfdchip capacitor in place. Solder the servoreversing switch in place making sure that the height of the switch lever matches the other two switches. Tin and solder the 5-inch servo wire to the 5K-ohm potentiometer (pot) noting that the center wire goes to the center tap of the pot.

Now, solder this assembly into the main pcb at the empty connector location in the upper left corner of the component side. Note that the center wire is swapped (crossed over) with the wire on the right side of the empty connector locationwhich is the side closest to the other connectors (see Diagram C). Remove the control-stick assembly and set it aside. Drill or melt a suitable mounting hole for the pot in the upper right corner of the case and install the pot.

Replace the stick assembly and remount the pcb. Reconnect the four off-board connectors. Tuck the servo wire leading to the new control pot along the left side of the stick assembly so it won’t get into the stick mechanics.

Position the back of the case and, working from the inside with your hobby knife, patiently score through the aluminum trim sheet that covers the molded hole for the 3-channel servo-reversing switch. Finally, replace the back of the case, battery cassette, battery hatch, crystal and antenna. Test the modification.

Remember, you are only going to use the center fifth of the pot’s resistance, which translates to about 70 degrees of rotation. Once tested, fashion a suitable lever assembly out of a knob and some scrap plastic (servo arms work great). At last, with your lever arm in place, add a few servo-mounting screws to physically limit the arm travel. Well done, and happy flying!

Chip capacitors and resistors can be difficult to find in single quantities in nonurban areas. If you would like a short kit of parts (except the switch, pot and knob) please send me a stamped, self-addressed envelope and $2. For a complete kit with expanded step-by-step instructions, send $13 to Alan McSwain, 3528 West Flower Ave., Fullerton, CA 92833.

*Addresses are listed alphabetically in the Index of Manufacturers on page 158.

Copyright Air Age Publishing Jan 1998

Provided by ProQuest Information and Learning Company. All rights Reserved