QRP Labs QCX 5W CW, Руководство по сборке, Страница: 124 / 138

QCX assembly Rev 1.08
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6.3 A row of blocks appears on the top row
If you see a row of blocks along the top of the LCD module, and the bottom row is empty, this
means that the microcontroller has not communicated with the LCD module.
Check that your IC2 microcontroller is correctly installed in its 28-pin socket, with the correct
orientation (dimple on the chip matches the dimple on the socket and the PCB silkscreen). Check
that all of the pins of IC2 are correctly inserted in the socket, not bent.
6.4 DC voltage readings
The following table lists the DC voltage read at various points around the
circuit. This may aid troubleshooting. The voltage measurements 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, right).
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.