[CAUT] yellow light issue - long post

[Elwood Doss]

Roger, I'm impressed!  Thank you for your concern and persistency in
solving problems with your product.

Joy!

Elwood

 

Elwood Doss, Jr., M.M.E., RPT

Piano Technician/Technical Director

Department of Music

145 Fine Arts Building

The University of Tennessee at Martin

Martin, TN  38238

731/881-1852

FAX: 731/881-7415

HOME: 731/587-5700

________________________________

From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of
Roger Wheelock
Sent: Monday, April 28, 2008 7:41 AM
To: College and University Technicians
Subject: [CAUT] yellow light issue - long post

 

Hello CAUTs,

 

Last week piano technician John Ross from Windsor, Nova Scotia provided
us with very useful information that has helped us make progress on
solving a minor, but persistent quality problem associated with the H5
Humidistat in our Piano Life Saver System.  The problem and our current
approach to eliminating it are detailed in the following discussion.

 

The challenge with a small percentage of the H5s is that upon
installation, the yellow low water warning light works fine.  However,
sometime after installation, the yellow light fails and will not turn on
when the water in the Humidifier is low.  Usually, this is discovered by
the piano owner who calls the technician stating one of the following
two things, either  "It has been a long time and the yellow light has
not come on to tell me to add water."  Or "the red light is on and the
yellow light has never come on".  The technician makes a service call
and finds the tank nearly dry in the first case and completely dry in
the second.

 

John encountered this problem, and happened to have two H5 Humidistats
in his shop that he could use for the replacement.  First, he decided to
test them in his shop and found that one of these failed within the
three hours time.  While this frequency of occurrence far exceeds the
rate we have seen in the field, the coincidence was very fortunate as
the information broke a technical impasse we were experiencing in
finding the root cause of the problem.

 

John and I talked on the phone at length about the issue.  He has had
some experience in electronics prior to becoming a piano technician.  He
thought there might be some sort of thermal effect underlying the
problem.  He suggested that proximity to a dehumidifier, as in a
vertical installation, might be providing heat to cause the problem.  I
explained that we had seen it in grand pianos on occasion, where the
Dehumidifiers are much farther from the Humidistat.  The idea of
temperature being involved was new and kept me thinking.

 

We set up tests where we sealed the vent holes on the Humidistats and
operated them overnight.  Sealing the vent holes allowed for excessive
heat build up inside the Humidistat.  The vent holes normally operate to
dissipate heat from the transformer on the circuit board inside the
Humidistat.  (The transformer was added to the H5 to meet the
increasingly stringent Underwriter's Laboratory  safety standards for
our product.)  However, the inside of the Humidistat does get slightly
warmer during operation.  With the vent holes sealed, the inside of the
Humidistat reaches a much higher temperature than during normal
operation.  Using this procedure we were able to duplicate the failure
in a small number of Humidistats in our in-house inventory.

 

I met with our design engineer, Keith Howell, and our senior electronics
technician, Randy Kaufman on Friday.  Under microscopic examination we
had previously observed hairline cracks in a capacitor in the yellow
light circuit in units returned to us from the field.  However, the
cracks were found in returns where we could not duplicate the problem as
well as in units where we could.  At our meeting on Friday we agreed
that the warming of the case during the first few hours of operation was
enough to widen such a crack and cause the circuit to fail.  While this
doesn't tell us what is causing the crack it gives us an excellent new
approach to investigate this more thoroughly.

 

Our next steps are as follows.  We are testing all Humidistats under the
extreme condition of having the vent holes sealed during overnight
operation.  Failures are removed from production and will be closely
analyzed for why they failed.  Gayle, our ten-year old son, Robbie and I
spent the weekend testing our entire inventory.  Product shipped from
our factory as of Monday, April 28th will be free of this defect.

 

We will begin testing bare circuit boards while hot to see if we can
reject them prior to assembly.  If they fail under these conditions, it
will show that the cracking of the capacitor is being done by our
circuit board supplier.  If this is so we will audit their factory to
determine where in their process the problem is caused.

 

If it does not appear on the bare boards, we will look even more closely
at our process to see if there is anything we are doing to cause a
physical shock to the circuit board that could create a hairline crack
in the capacitor of concern.  We have studied our process closely and do
not see anything of concern.  However, the recent thermal hypothesis and
the use of heat in our testing will finally allow us to make a
definitive determination and move forward.

 

John has suggested that technicians test Humidistats in their shops
prior to installing the System.  This seems like a prudent idea until
old inventory works its way through the distribution system.  Simply
place the Humidistat in an upright position (vents facing upward as in
normal installation).  Plug in the two-light panel and let the
Humidistat run for a couple hours.  Contact us at 800-438-1524 if you
encounter a problem and we will quickly furnish a replacement.

 

I am grateful for John's input to the situation.  It really has made a
difference.  Thank you, John.

 

If any of you have encountered this situation in the field, I apologize
for the frustration you must have experienced.  Also if you have a
return that you have not sent back to us, please do.  It will help us
solve this permanently at its root cause, rather than eliminating the
defect through testing at the end of our assembly process.

 

I welcome your comments, concerns and suggestions.  Please contact me
off the list at roger at dampp-chaser.com.

 

Sincerely,

 

Roger Wheelock, VP

Dampp-Chaser Corporation

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