Page
2
of
25
The two most USEFUL diagrams for fault-finding, are the circuit diagram, the parts layout diagram, and the tracks
diagram. Remember that on the tracks diagram, BLUE tracks are on the bottom side of the board, and RED tracks are on
the top side of the board. These diagrams are in the manual already. But here they are again, just so you have them near
at hand.
Click the diagrams to see the larger version; or even better, right-click "Open in new tab" or "Open in new window" etc.
Equipment
I use an oscilloscope for detecting the signal at each point through the signal path. Some of this trouble-shooting will be
quite difficult without an oscilloscope. You can still use a DVM for some measurements (or the internal DVM of the QCX
itself, provided you have the digital section working properly). You do not need anything else - the QCX has its own built-
in Signal Generator.
General checks before starting
It is worthwhile to check once again, that all of the IC's are properly orientated, with their dimple matching the one on the
PCB silkscreen; and examine the PCB carefully, using a bright light and optical magnification (for example, Jeweler's
loupe, magnifying glass or USB microscope). Look for any dry joints, solder bridges, any component wires which were
snipped off slightly too long and might touch each other and cause short circuits.
There are a lot of parts to solder and it is surprisingly easy to forget to solder a component wire! Or even forget to install a
component completely! It has happened time and again. A quite nice trick is to hold the PCB up in front of a bright light.
As you look through the board, you will see the sparkle of the light through any holes which have not been soldered. It is a
neat trick that really helps find any forgotten joints and it takes only a moment. Don't panic though - remember that band
pass filter capacitors C5 and C8 are not always installed (depends on the band).
