On Mon, 22 Feb 2010 14:41:01 -0600, Jon Elson
wrote:

Ned Simmons wrote:
One axis on my grinder readout is reading erratically and the symptoms
point to the pulse detection/shaping circuit being out of alignment.
The scale indicates approximately the proper distance travelled, but
only counts in one direction. In other words, move forward 1 inch and
the readout will indicate approximately 1.0000; move back to the
original position and instead of returning to 0.0000 it reads, more or
less, 2.0000.

I've swapped scales and the problem follows the scale, not the readout
channel.

The scales are Sony p/n SR-2711 and the readout is an LF-200. I
believe they date from around 1985.

Does this have a smooth rod as the scale and a read head with a hole in
it that slides over the rod?

That's the one.

If so, the rod is not symmetrical, the
magnetic "whatever it is" is polarized on the side of the rod. So, try
turning the rod in small increments, like 30 degrees, until it starts to
count better. There is a read head floating inside the outer shield
box, and it can get knocked out of alignment and ride crooked on the
rod. There should be a strip of spring steel that can be bent so the
head rides parallel to the rod.

The scale is very heavily built and has a rather elaborate suspension
system for the rod. It'll take a bit more diassembly to see what's
required to rotate the rod. Thanks for the tip.


--
Ned Simmons