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I think this has been mentioned before but be careful when
checking for shorts around IC's. Some multimeters feed out up to
15 Volts across the test probes which can blow a sensitive IC
before you even start to assemble your kit.
I am amazed that a stray resistor leg shorted the 12 Volt line
to the 5 Volt line. Does the manual not mention that the surplus
length is cut off.
I use a bleeper designed by W4ZCB ( now sadly a SK) to check for
problems which has a very low voltage across the test probes on an
open circuit and only a few micro-amps on a short circuit.
Hans has mentioned in the past that the number of QCX's sold is
around 4000 but given the number of builders who have purchased
several units, the true number of purchasers must be only a few
On 11/12/2019 14:20, Nick Austen wrote:
Summary: check for shorts between legs of the surface mounted
devices before you start (additional cautionary note to add to
Background: I first bought and built one 40m QCX - all worked
first try - then accidentally blew it up with a stray remnant
resistor leg shorting 12v to 5v - now fixed after replacing the
processor, and other digital chips as well as voltage dropping
diodes (first replacement Si5351A replaces twice as first
replacement did not oscillate at crystal frequency). All perfect
Then bought two more (one to give as a gift). I built them in
parallel. Neither worked (initially).
After searching and checking, I looked at the quadrature outputs
of the Si5351A’s. One unit had an odd looking three-level signal
on the oscilloscope- which I eventually realised was the sum of
the two quadrature outputs - they were shorted.
After careful magnified viewing I saw a short right on the pins of
this synthesizer (not put there by me).
Solder wick fixed that quickly.
The second unit had only one of the quad outputs oscillating- the
other was at 0 vdc. Found another short - this time from the
second quad output to the ground pin. This was also fixed by
quick application of solder wick.
All working now - phew.
Conclusion - don’t let it put you off - just check the legs of the
Si5351A on the bare board before you start - it may save you some
Still highly recommend - the best kit I have seen.