Once the main board has
been assembled, it's simply a matter of completing the small front-panel
board, wiring them together and completing the assembly. But first, there are a
couple of minor modifications to the main board. The accompanying panel has the
Front panel board assembly
Referring to the overlay diagram (Fig.9), begin by installing
the 11 wire links, followed by the resistors. Next, turn the board over and
install the two remaining resistors on the bottom (copper) side, as shown in
Fig.10. Cut the protruding resistor leads off flush with the surface of the PC
board (on the top side).
Moving back to the top side, install the connector (CON7)
followed by the 33μF tantalum capacitor. Mount the capacitor horizontally rather than
vertically and fit a short length of heatshrink tubing over its negative lead to
ensure that it cannot short out on nearby components.
Transistors Q5-Q8 can go in next, followed by the four
pushbutton switches. It is particularly important that the base of each switch
is seated firmly on the PC board surface during soldering. Be sure to install
the red switch in the S4 position and make sure that the flat side of each
switch is oriented as shown.
Fig.9: overlay diagram for the front panel PC board. The 33μF capacitor must be mounted horizontally (see above photo), with heatshrink tubing on its leads to prevent short circuits. Note that the lefthand and righthand columns of LEDs are orientated differently.
The final step involves mounting all the LEDs and fitting the
board to the front panel. Start by installing each LED in place but do not
solder or cut the leads short just yet. Note in particular the orientation of
the anode and cathode leads for each column of LEDs-
they differ between the
lefthand and righthand columns, as indicated in Fig.9.
Follow the details in Fig.11 to mount the PC board to the front
panel. That done, place the face of the panel on a flat surface and push the
LEDs into their designated panel holes. If you would like the LEDs to protrude
through the panel slightly, then raise the panel the desired amount and push the
LEDs through until they contract the flat surface below. Solder them into
position to complete the job.