[Elecraft] K2 RF board resistance check - RYCOM

[Wallace, Andy]

> -----Original Message-----
> From: Charles Vollum [mailto:moana@xsw.com]
>=20
> After much searching I've narrowed the location of my problem=20
> to one of C207's pads.  This pad connects to K10 pin 10 and U1 pin 17, =

> and shows about 6 ohms to ground.  Cutting both traces still leaves =
this=20
> resistance unchanged.  I've put some closeup photos of the=20
> pad from top and bottom on the web at
>    http://xsw.com/k2/c207
>=20
> I don't see anything funny about the hole or it's plating, but=20
> something is obviously going on.

I sent Charles a direct reply but am sending this one to the List.
People, take a look at his shots, and click on the right hand
one to enlarge. That's the top side.=20

Now look very carefully at the highlighted hole. The bright silver
(tinned) pad looks great, but the green solder mask covers the area
around it. See how there's a bulging "halo" of copper underneath
in the 7:00 - 8:00 position?

Now look carefully at the 1:00 position. It looks like there's a similar
bulge, except this one is big and sure looks like it's touching the
ground area nearby. I bet that's where the short is. I told Charles
to scrape the point of an x-acto knife around the pad.=20

This photo is a great example of what can crop up occasionally.
I will say (and most would agree) that the Elecraft boards are
great quality and this kind of thing is probably extremely rare.

I built a Ten Tec 30m QRP kit several years ago and had a similar
short, which was not only under the solder mask, but it was under
the silkscreen for the component outline! Troubleshot to the pin
and eventually found it.

Andy