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If the processor is present and orientated correctly, the next thing to check for is that all the pins are properly inserted into
the socket. We did have one or two cases where the 28-pin socket was missing a pin. A manufacturing defect.
Presumably you would have noticed that during soldering - but just check again now too. When the chips arrive from the
factory, the legs are slightly splayed outwards. It is necessary to gently squeeze them inwards so that they fit in the
socket. It is quite easy to push the chip in the socket, and not notice that one of its legs has bent inwards rather than
properly going into the socket. So check that all the pins are nice and straight, and all are properly in their sockets. If any
pins of the processor are not properly connecting with the socket - then this cause the processor to fail to start; it can also
cause many other kinds of failure too, depending on which pin it is, that is not connecting.
Unreliable processor boot up
A common cause of the processor failing to start up, IF your board is a Rev 1 or Rev 2 PCB, is described by
, to ensure reliable processor startup. On the Rev 3 PCB, this modification is already included
as standard, so this paragraph doesn't apply. Whenever I am fault-finding a QCX, if it is a Rev 1 or 2 PCB, I always
implement this modification first, before anything else.
If that doesn't help, you can also check that the 20MHz crystal is oscillating. This can be done with an oscilloscope with
x10 probe at IC2 pins 9 and 10 (NOT a x1 probe, which will load the crystal oscillator pins of the processor too much).
You could also listen for the signal at around 20MHz, with a general coverage receiver. But bear in mind it will likely be
several kHz off frequency, so tune around for it.
Right at the END, you can suspect that the processor is faulty. This does happen but is rare. My GENERAL RULE is that
we intuitively always want to suspect defective components, rather than our own mistakes in assembly; but when we find
out what is wrong, it usually turns out to be OUR MISTAKE, not a defective component! We want to make this work, not
massage our ego... so always suspect defective components ONLY as a last resort when all other avenues of
investigation are exhausted.
When the processor boots up, the first thing you will see, is the question about which band to select. You have to turn the
rotary encoder to select the band you built the kit for. It is important to select the correct band, NOT to choose the wrong
band then tune to the one you really want, using the rotary encoder. This is because the firmware adjusts the Si5351A
commands for the chosen band, in the configuration which generates 90-degree quadrature oscillator signals; but this
configuration must be altered for very large frequency changes, such as to another band.
Wrong band selected
If you chose the wrong band, the best way to recover the situation is to undertake a factory reset using menu item 7.8,
then turn the power off, and on again, and this time select the correct band.
Buttons / rotary encoder don't work properly
If you discover that you cannot operate the buttons correctly, or the rotary encoder does not work as expected - then this
can occur also due to the lack of the reliable
processor start-up modification
, on a Rev 1 / Rev 2 PCB. See above. It is
important to realize that even if the processor appears to have booted up properly, and is writing to the LCD etc., in some
cases the unreliable start-up issue can mean that the Analogue-to-Digital Converter (ADC) subsystem does not work
properly. Reading the three buttons depends on the ADC. If the ADC is not working, then the buttons will be mis-read, or
not read at all. So again, it pays to
RECEIVE signal path
Failure to get BPF peak, or a high enough signal strength reading
The best way to check that the receiver is working, is to use menu item "8.7 Peak BPF". If the displayed signal strength
shows at least 8 or 9 in the display top right corner, and if you hear a loud tone in the earphones (do NOT put them in your
