Re: Hum on new build

Ken KM4NFQ
 

Hello Curt KB5JO,

When I solder a project, I always do it one component at a time, and
my solder joints bleed through to the top of the PCB a wee bit. Then I
clip the leads and check the soldered part with a magnifying glass
before I place the next part. I checked all the parts with test
equipment before they were soldered. All of them were well within
tolerances, AFAIK. Anyway, I checked again, and I did not miss any
solder joints. The BNC connector is soldered to the PCB very well, as
are the battery terminals, and the audio jack.

I suspect the part of the circuit with the headphone driver to be the
culprit? I did not solder the IC directly to the PCB, I soldered an
8-pin DIP socket to the PCB, then attached the IC to the socket. That
is the only thing I did that deviated from the assembly guide. Which
component(s) do you think might be suspect?

I can probe (circuit-bend?) parts on the Pixie and get different
things to happen. I have not probed the Cricket 40 (yet). I get the
background hum when I use a 9V battery AND when I connect the Bench
Power Supply to the battery terminals.

I think I can live with the background hum. I bought the kit because I
think it is beautiful. It was not that difficult to put together, and
I had an enjoyable time doing so. I was really just curious to know if
that background hum was normal? Is your Cricket silent except for the
CW signals?

Regards,
Ken, KM4NFQ "Not Fully Qualified"
https://groups.io/g/w8bhMorseTutor

On Mon, Feb 17, 2020 at 7:49 AM Curt via Groups.Io
<rhulett1=consolidated.net@groups.io> wrote:

Ken,

Well if the Pixie doesn't hum with your antenna system but the Cricket does, that points to a problem on the Cricket somewhere ( they are supposed to chirp not hum [lol]).

Seriously, there must be a connection that isn't properly terminated, especially to the ground plane of the board. For example, is the shield of the onboard antenna jack well soldered to the board ground? So, what I would suggest is to go back over all the soldered connections with a hot soldering iron, just to remelt each. Sometimes you can push and prod at components with an non-conductive "tool" to identify the culprit. My favorite tool is a bamboo skewer.

I have built a lot of electronics scratchbuilt and kits, from pixies up to a K2. Nearly every problem encountered was due to poor or missing solder connection. Missing a connection with the soldering iron has happened many times. I even once encountered a connection with no solder on a 55 year-old Drake R4 receiver while troubleshooting an intermittent receive problem, the factory had evidently missed it.

Repairing a malfunctioning radio is one of the most satisfying aspects of this hobby.

Curt KB5JO

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