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 details.

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.