Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old September 26th 05, 12:30 AM
Ralph Mowery
 
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Default Are these solder joints bad?


"Van Chocstraw" wrote in message
...
I'm attempting to locate a problem on my Dell D1025TM UltraScan
(Trinitron) monitor. I posted about it a week and a half ago. I got
the D board out and am checking for bad solder joints.

I'm not sure if these should be re-soldered or not. If so, what's the
best way to get the crud off the pads and surrounding areas? Will
acetone do it?

http://www.eztapes.com/d1025tm/

Is the residue rosin that has seeped out of the solder itself as a
result of thermal cycling over a period of years? I notice that all of
these solder joints are for components that get hot while the monitor is

on.

I realize there may be other cold solder joints that don't appear to
have anything wrong with them at first glance, unlike these, but these
got my attention first. I realize these may not be "cold" at all.


The rosin will not seep out of the solder later on. It does look like the
joints got hot and sort of melted and burnt. This hapens when the design is
slightly wrong and the components get the joint too hot over the years. Try
to clean off the solder and put on some new solder. You may have to scrape
the leads and pads to get them clean enough.



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Old September 26th 05, 12:39 AM
CJT
 
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Van Chocstraw wrote:

I'm attempting to locate a problem on my Dell D1025TM UltraScan
(Trinitron) monitor. I posted about it a week and a half ago. I got
the D board out and am checking for bad solder joints.

I'm not sure if these should be re-soldered or not. If so, what's the
best way to get the crud off the pads and surrounding areas? Will
acetone do it?

http://www.eztapes.com/d1025tm/

Is the residue rosin that has seeped out of the solder itself as a
result of thermal cycling over a period of years? I notice that all of
these solder joints are for components that get hot while the monitor is
on.

I realize there may be other cold solder joints that don't appear to
have anything wrong with them at first glance, unlike these, but these
got my attention first. I realize these may not be "cold" at all.

Appreciate any and all comments. Thanks!

VCS


FWIW, they look fine to me. I'd look elsewhere for the problem.

I wouldn't worry about the rosin unless you're in an extremely high
humidity area, and maybe not even then.

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Old September 26th 05, 02:45 AM
 
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Dirty component leads exposed to RF at high voltages can eventually
isolate themselves from their solder connections. This also happens
with gold-plated leads.

#5 looks like a cold joint to me, but it is hard to tell from the
photo; it could just be too much solder. The top one in #2 also looks
bad, but it looks like a filter cap from your description and you'd
probably know if it was bad.

Rosin left on the circuit board will eventually corrode exposed metal,
but it happens over a period of decades.

The easiest way to re-do these (should you decide to go that route) is
probably to just add a little liquid flux, reheat the joint, and then
clean up afterward with IPA or flux remover. Acetone works great, but
it can take off the conformal coating and silkscreens too.

I once worked on a monitor I knew had a cold joint (it was losing
deflection and beating on it made the problem appear and disappear).
The one that was bad was one I'd looked at half a dozen times. I only
found it by tapping around the board with a dowel.

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Old September 26th 05, 03:44 AM
 
Posts: n/a
Default

Ignore this poster. It's a troll.


Van Chocstraw wrote:
I'm attempting to locate a problem on my Dell D1025TM UltraScan
(Trinitron) monitor. I posted about it a week and a half ago. I got
the D board out and am checking for bad solder joints.

I'm not sure if these should be re-soldered or not. If so, what's the
best way to get the crud off the pads and surrounding areas? Will
acetone do it?

http://www.eztapes.com/d1025tm/

Is the residue rosin that has seeped out of the solder itself as a
result of thermal cycling over a period of years? I notice that all of
these solder joints are for components that get hot while the monitor is on.

I realize there may be other cold solder joints that don't appear to
have anything wrong with them at first glance, unlike these, but these
got my attention first. I realize these may not be "cold" at all.

Appreciate any and all comments. Thanks!

VCS


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Old September 27th 05, 10:42 PM
 
Posts: n/a
Default


Most computer manufacturers are using a no clean solder flux. It's OK to have
it and if you attempt to remove it, it reactivates and can become
corrosive to the PC board traces.

b.


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Old September 29th 05, 04:51 PM
Asimov
 
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Default

" bravely wrote to "All" (25 Sep 05 18:45:13)
--- on the heady topic of " Are these solder joints bad?"

st From: "
st Xref: core-easynews sci.electronics.repair:343123
[,,,]
st Rosin left on the circuit board will eventually corrode exposed metal,
st but it happens over a period of decades.
[,,,]

Acid flux will certainly corrode metal but rosin flux made for
electronics is pretty inert. I've seen older circuits with a lot of
residue rosin and they worked just fine.

The main problem I have experienced with rosin was in a high impedance
application because rosin will absorb and trap humidity thus lowering
circuit resistance. Perhaps this trapped humidity might explain the
corrosion you have seen on metal?

A*s*i*m*o*v

.... Who's got the Thermonuclear Welding Set? - ToddS

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Old September 29th 05, 07:31 PM
 
Posts: n/a
Default

I personally don't believe it either.. but I was first told this when I
was certified for mil-2000a soldering, and all of my research on the
topic has confirmed it. It's the residue, which consists of flux and
various other substances, some of which were formed during soldering,
that are considered corrosive. Most QA programs specify that all flux
residue has to be removed. However, there are different kinds of flux.
Plain old rosin is supposed to be totally benign. RA and RMA are more
chemically aggressive, and are not recommended for no-clean
applications. No-clean fluxes have the benefit of omitting the cleanup
step, but they are bad for soldering iron tips (go figure).. and my
iron was pretty expensive so I use RMA and scrub it off when I'm done.

This is all going to change really soon because of the industry push to
RoHS anyway.

And was this really a troll post? How can you tell? Somehow I just
don't feel properly burned...

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Old September 30th 05, 04:50 AM
Jim Adney
 
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Default

On Thu, 29 Sep 2005 15:51:06 GMT "Asimov"
wrote:

Acid flux will certainly corrode metal but rosin flux made for
electronics is pretty inert. I've seen older circuits with a lot of
residue rosin and they worked just fine.


I have to agree. I've got stuff here that I made 50 years ago,
soldered with rosin core electronic solder that is still fine with no
sign of corrosion. That was point-to-point wiring. I have plenty of
later stuff that is PC board done 30 years ago that is also fine.

But I don't know what kind of flux was used in standard elecronic
rosin core solder. Was it RMA?

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------


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