QRP Labs QCX-mini CW, Руководство по сборке, Страница: 107 / 121

were made using the in-built DVM, in menu item 9.1. These measurements were made
using a 12V power supply.
Where an IC pin number is mentioned, remember that pin numbers start from the top left
(just to the left of the dimple at the end of the chip) and are counted anticlockwise from
there (see diagram of 8-pin IC for example, on previous page).
Where “left”, “right”, “top” and “bottom” are mentioned, they assume the PCB is orientated
in the normal way.
All measurements were made probing the PCB from the top side. In some cases, poke the
wire to touch the pad of a particular capacitor or resistor.
References to the pinout of transformer T1 use the
nomenclature indicated in the diagram (right).
In many cases these measurements may not
exactly match your own. In particular if you use a
power supply other than 12V, then voltages which
are derived from the 12V supply line will be
different. For example, bias voltages on op-amps
which are biased to half the supply rail.
Bear in mind that in some of these measurements,
the act of measurement will itself change the
measurement. The “input resistance” of this DVM is
only 13.3K (R56 and R57 in series, assuming high
input resistance of the microcontroller pin). If you
were to make these DC measurements with a high input resistance “real” DVM rather than
the inbuilt DVM of this radio transceiver, these measurements would change. Again: if your
measurement is in the right ballpark, do not worry if it differs from these.
When making these measurements, be very careful that whatever wire you are using to
probe the circuit does not cause shorts to adjacent pins or components, which could cause
damage.
I suggest avoiding directly probing the Si5351A chip pins, they are just too small: the risk of
shorting adjacent pins is high. You can easily probe nearby components which are
connected to the Si5351A pins, if you wish – refer to the PCB tracks diagram. Similarly, I do
not recommend directly probing the FST3253 pins. Again, it is easy to probe nearby
components which are connected to those pins, and reduces the risk of damaging
something by causing inadvertent short circuits.
QCX-mini assembly Rev 1.05
107