On Wed, 24 Aug 2011 16:41:57 -0700, Winston
wrote:
micky wrote:
On Mon, 22 Aug 2011 20:42:34 -0700,
wrote:
(...)
The second guy acutally has an enalarged photo of the circuit board
with several joints marked and the symptoms when each is bad, whn you
hold the cursor over the circle! This must be a really common
problem.
http://techauto.tripod.com/mainrelay.htm
And a big tutorial on bad solder joints and resoldering.
I agree with just about everything presented on that page.
This relay board is likely to be corroded in the defective
joints, so I certainly see that removing the old solder
is a very Good Idea.
However:
1) Dab compatible flux on each joint before soldering.
A) I use standard old rosin flux so I selected a
matching liquid flux. I apply it from a HDPE
flux bottle.
http://assemblyoutfitters.com/images...lux-bottle.jpg
For maximum convenience, the stuff is available
in 'pen' form too:
http://theledguy.chainreactionweb.co...-1000-0186.jpg
I'll look for one of these. I have some liquid flux, but I can't
remember ifit's for electronic soldering, or copper plumbing! I'll
check. It's by Oatey, so I guess it's for plumbing. :-) I'll see
if I can find some flux before Sunday.
2) The advice to clean the board with steel wool is
extremely risky. Fine metal hairs are not something
you want in an electronic assembly. Use an acid
brush and a flux bottle full of 50/50 alcohol/naphtha.
I hadn't read that line yet, but I think I would have had sense enough
not to do it. Thanks for warning me.
But there are wackos who do great detail work too, so I didn't take
his oxide story seriously until you guys confirmed it.
In either event, it is critical to apply separate flux
to the joint to float oxides out during the soldering
process. The improvement in quality is substantial.
I see.
(...)
A 2001 Honda Accord EX, but all Hondas for the last 15 years seem to
use this part.
(...)
Honestly, I dab flux on the joint and reheat. It is quick
and effective. For joints that appear cold after that operation,
I remove the old solder, re-flux and use good quality leaded
solder. (Then *always* clean with a 50/50 mix of alcohol and naphtha).
Dang. I never clean joints I have soldered. 
I don't think
anyone ever told me to before.
Fluxes work by dissolving metal and suspending oxides.
They don't know when their job is complete. Sooooooo.... 
(....)
Thanks, and thanks everyone.
Please let us know how it goes.
She works almost every day, so iIt's scheduled for Sunday now. The
weather says that Hurricane Irene will be off the coast of Delaware
about that time, but I can't tell if it will be raining hard in
Baltimore or not.
If the weather is good enough, maybe I can let you know by then.
--Winston