[analogorgans] Re: Cipher....
- From: "Thomas W. Nelson" <twnelson@xxxxxxxxxxxx>
- To: analogorgans@xxxxxxxxxxxxx
- Date: Mon, 20 Jun 2005 16:28:52 -0400
Jean Moquin wrote:
Just to share.....This occured on a Rodgers model 220-II
that I am restoring. A permanent cipher had developed. This affected
key no. 41 on the "swell unit trompette / reed" ( 8' ). I checked and
rechecked every circuit and components in the signal chain. The cipher
was sounding at the correct pitch, but at a somewhat lower level than
when the key was pressed down. This seemed puzzling since the voicing
circuits here are used by three stops (4', 8', and 16' reeds).
I finaly started looking for amore "obvious" or simple thing
than a deffective component....a broken or shorted part of the
circuitry...Looking with a magnifiying glass,I finaly found that two
solder paths, located at the back of the voicing pannel may have
developed some conductivity...maybe just some oxydation did
this....Just scraping between these paths with the tip of a testing
probe corrected this cipher....
Not as obvious as a broken connection!
My suspicion would be that there was some solder flux from an earlier
repair left on the PC board that provided a place for conductive
oxidation to grow over time, especially if the instrument has been
stored in a potentially humid environment for some time.
One of the important things that I learned as both a electronics service
tech and later as a digital/analog hardware engineer was the importance
of removing excess flux after construction or repairs to the long-term
reliability of the circuitry. The tin/lead solders used up until a
decade or so ago can hold lead particulate in suspension in the resin
flux, causing the problem you observed. It's similar to the lead oxide
blooming on organ pipes. Modern 90%+ tin solders don't exhibit this
problem, but should still be cleaned up after repairs as a practice. A
good hosing with board flux cleaner or even denatured alcohol is sufficient.
-- Tom
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