D.G. Nova update... disk drive again

Tom Jennings tomj at wps.com
Thu Apr 7 02:47:16 CDT 2005


On Wed, 6 Apr 2005, Dwight K. Elvey wrote:

> I know that you'd like to blame the capacitors but
> if these were all bypass capacitors, it is unlikely that
> they are the source of your problem.

Well, pretty much all of them were... but there are also other
caps of the same type that I did not replace, as I didn't have the
values. I do believe at this time that the problem is on the
analog board. There are three chips, functioning, a bunch of 1/4w
Rs, some diodes, etc, that I "trust".

I did replace one .01 with .1 that was the DC block to the AGC; I
overlooked that until the board was installed. That's a flat-out
mistake.

So I ordered the right caps, including the missing values, and
since it's an overall "low cost" job, I'll do it somewhat blindly.

And worry anew if it doesn't work :-)

I did watch the AGC work, but you know how that goes; it's a
closed-loop, the reference V for it seems OK, I saw a long-TC
sniggle (tens of millsecs) so I "assume" AGC works.


> I expect that the culprit is moisture. When the unit is always
> powered, the heat of each part keeps moisture from accumulating
> within the plastic IC packages. When turned off for some
> time, moisture builds up inside the parts. When power
> is applied, this causes some electrolysis inside that destroys
> the part.

Well, it was a truly well-sealed trailer. In Bakersfield. Think
hot desert (though there is winter rain, 8" a year or so, there
was not one single evidence of moisture, zero, not even mouse
turds). Absolutely no evidence of humidity, all the papers were
dry and clean.



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