Ditto for the early Chrysler Sebring/ Dodge Stratus instrument panel. A
pair of PTH power resistors on the backside of the instrument cluster
PWB would heat cycle, vibrate and open up at the solder joints. This
would intermittantly make the odometer go blank and shut off the tach. A
lot of clusters were swapped out because of it. Only 30 sec. with a
soldering pencil would solve the problem.
Neil Maloney, Manufacturing Engineer/
LAN Administrator
Contemporary Control Systems, Inc
2431 Curtiss St Downers Grove, IL 60515
(630) 963-7070 x132
[log in to unmask]
http://www.ccontrols.com
http://www.ctrlink.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Tuesday, July 14, 2009 11:15 AM
To: [log in to unmask]
Subject: Re: [TN] NTC (It's not Friday, but this is so true!)
Wayne,
this was a classical High Current/High Temperature/Solder
Decomposition/Fatigue issue. (Is there one word for this?). Famous
failure,
world wide during a couple of years with Philips Z12 TV chassis many
years
ago. Philips decided to solder mount the image frequency transformer by
means of a number of pins in through holes on the PWB. The transformer
was
very warm, heavy and lots of current passed through the pins. The
transformer had no screws or bolts, was just hanging in the solder
joints.
After some time, the solder joints looked EXACTLY like the one in my AC
controller board. Those who were familiar with the technology at that
time
knew what to do: open the TV swing out the monster chassis, suck up the
old
solder around the transformer pins and redo the soldering. This had to
be
repeated once a year or so. Philips made a redesign and fixed a
mechanical
suppor which removed all mechanical force to the solder joints. All old
dogs
recognize this kind of issue, younger don't .
AND....this type of failures exist still. The below lines are written
just a
few years ago:
TV and Monitor Manufacturing Quality and Cold Solder Joints
Low cost no-name (or unknown name) computer monitors tend to be
particularly
prone to bad solder connections. However, so are many models of name
brand
TVs including those from RCA/GE/Proscan and Sony. We'll touch on these
at
the end of this article.
Any intermittent problems with monitors that cause random sudden changes
in
the picture brightness, color, size, or position are often a result of
bad
connections. Strategically placed bad connections can also cause parts
to
blow. For example, a bad connection to the SCR anode in a phase
controlled
power supply can result in all the current passing through the startup
resistor, blowing it as well as other components. I had a TV like this -
the
real problem was a bad solder joint at a pin on the flyback. Thus,
erratic
problems, especially where they are power or deflection related, should
not
be ignored!
Bad solder joints are very common in TVs and monitors due both to poor
quality manufacturing as well as to deterioration of the solder bond
after
numerous thermal cycles and components running at high temperature.
Without
knowing anything about the circuitry, it is usually possible to cure
these
problems by locating all bad solder connections and cleaning and
reseating
internal connectors. The term 'cold solder joint' strictly refers to a
solder connection that was either not heated enough during
manufacturing,
was cooled too quickly, or where part pins were moved before the solder
had
a chance to solidify. A similar situation can develop over time with
thermal
cycling where parts are not properly fastened and are essentially being
held
in by the solder alone. Both situations are most common with the pins of
large components like transformers, power transistors and power
resistors,
and large connectors. The pins of the components have a large thermal
mass
and may not get hot enough during manufacturing. Also, they are
relatively
massive and may flex the connection due to vibration or thermal
expansion
and contraction.
Why Can't TV Manufacturers Learn to Solder Properly?
I can think of several potential reasons - all solvable but at higher
manufacturing cost.
1.. Mass of large component leads (like shields) does not get
adequately
heated during manufacture leading to latent cold solder joints. While
they
may look OK, the solder never actually 'wetted' the heavy pins and
therefore
did not form a good mechanical or electrical bond.
2.. Thermal cycles and differential thermal coefficients of circuit
boards, traces, and solder. While it is not easy to do anything about
the
material properties, using plated through-holes or a similar mechanical
via
would greatly increase the surface area of the joint and prevent the
formation of cracks.
3.. Vibration. This is also directly related to the single sided
circuit
boards without plated through-holes to strengthen the joints.
4.. Lack of adequate mechanical support (single sided circuit boards
without plated through-holes (vias).
I believe that the single most significantimprovement would come about
by
using plated through-holes but this would add to the cost and apparently
the
consumer is not willing to pay more for better quality and reliability!
Some
designs have used rivlets - mechanical vias instead of plated ones.
While
this is good in principle, the execution has often been flawed where
cold
solder joints resulted between the rivlets and the circuit board traces
due
to lack of adequate process control.
The Sony and RCA/GE tuner shield problem is interesting because this
could
have been solved years ago at essentially no additional cost as other
manufacturers - and their own repair procedures - have proven.
The End
Inge
----- Original Message -----
From: "Thayer, Wayne - IIW" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, July 14, 2009 4:02 PM
Subject: Re: [TN] NTC (It's not Friday, but this is so true!)
Hi Inge!
I am also someone who takes stuff to pieces. You should see the scars
on my
knuckles from all of the sheet metal cuts you can get on a car.
Now that you've put your car back together....
Are you absolutely sure the solder joint was bad when it left the line?
I
mean, the rest of the joints look just fine, so what is it about that
one?
In all liklihood this was wave soldered.
What if the real problem is that too much current is going through that
joint, which is considerably smaller than the adjacent joint on the same
trace? You may have only peeled back the first layer of the onion!
I hate to put doubts in the mind of someone who did an excellent job
getting
the thing repaired, but I know you are tough!
Wayne
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Tuesday, July 14, 2009 3:55 AM
To: [log in to unmask]
Subject: Re: [TN] NTC (It's not Friday, but this is so true!)
Inge - wow! It's all in the hunt! Good find!
Steve - You are right! That is a cool trailer!
Steve C
http://stevezeva.homestead.com/files/Inge_s_Car_Fun_.pdf
http://stevezeva.homestead.com/files/Unusual_Trike.jpg
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