Debug and Repair

VISUAL INSPECTION

The first task assigned to the debug team is to do a visual inspection of all circuits to find obvious problems. Before they began their work, two types of such problems were known, more types may be found. (Click thumbnails below for larger images. Click the Back button on your browser to return.)

1. Leaking capacitors
   These capacitors are on one of the tone generator boards. Similar problems have been found on the modular filter cards on the tone changer boards as well. There are approximately 150 boards total. Each will be inspected, leaking capacitors identified, value noted (the ones shown here are 0.22 microfarads), and a list compiled of needed replacements. The bad components will then be desoldered and the new ones soldered in place.
   
   
2. Loose wires
   No clue where that wire was supposed to go. It appears never to have been connected at all.
   
   Who knows how many more anomalies we will find when all of the boards are checked.

Results of the visual inspection (completed Feb. 28, 2006).

Bad Capacitors

The major result of the visual inspection is the number of capacitors that need to be replaced. Assuming the final count is accurate, there are 757 capacitors in need of replacement. Many of these are deteriorating and leaking (see above), but some need to be replaced due to the technology used. Particularly for the larger values, electrolytic types were often used, which is not a good choice for the resonant circuit in an oscillator for a couple of reasons. The most common value needing replacing is 1.0 microfarad, with a total of 328. I feel certain that electrolytics were chosen due to lower cost, but capacitors with some form of plastic dielectric (polystyrene, polypropylene, polycarbonate, poly-etc.) are a much better choice in this application since they are more stable and less lossy.

Will beginning the visual inspection of the 16' Solo rank.

Misplaced Items

Within the first hour, Will found that the lowest octave of the Solo 16' rank had the capacitors on half of the notes (F# - B) reversed. (F# had the capacitors for B, G had the capacitors for A#, etc.) It is amazing that these were actually tunable. He has also discovered discrepancies between the tone changer filter cards and the stops installed on the console. With the visual inspection of all tone changers and generators complete, quite a few difference have been found between stop tab labels and installed filters.

Example:

Photo of 16' Solo stop tabs.

The Flute Conique and Bass Violin Tabs come from filters labeled
Stopped Flute and Theater Violin on the tone changer board.
Obviously the same tone families, but how much difference this makes in voicing is yet to be determined.

Corrosion

A direct result of leaking capacitors. The green stuff is evidently copper oxide when the leaking electrolytes reacted with the copper traces on the boards.

Quite of few such boards will need cleaning before new capacitors can be soldered in.

REPAIR

Adam , Dan , Chris , Bradley , and Will working to remove bad capacitors and solder in new ones.

The goal for the Spring 2006 semester is to have at least one unified rank (hopefully more) repaired, reconnected to the console, and tuned so that the instrument can be played. It is unclear at this time whether or not this goal will be acheived.

Stay tuned!

This page last updated at 1:52 PM on Mon, Apr 23, 2007
CHORD site maintained by Dr. William Park. Please address comments or suggestions to parkw@ces.clemson.edu