Re: Soldering: a technical question


Arfa Daily wrote:
"moonlite" <elect21st@xxxxxxx> wrote in message
news:1159287557.599863.132760@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Arfa Daily wrote:
"moonlite" <elect21st@xxxxxxx> wrote in message
news:1159251375.570656.307640@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I'm working on a high end DVD player. It seems I am unable to make the
solder joints on the board take solder no matter what I do. I even
tried to add solder to the joints hoping that would help in the
desoldering process but they simply won't take. Is it possible this
board is manufactured differently to make servicing not possible
without specialized tools only ASC's have them ?

moonlite


If it is an up to date machine, then it will be manufactured using the
dreadful new-fangled save-the-planet brigade's lead-free solder. In order
to
repair it with any hope of long term chemical stability of any reworked
joints, you will need to be using using lead-free solder to rework them,
and
in order to do this, your iron will need to be around 30 deg C hotter
than
it needs to be for standard leaded solder. If you look carefully at the
board with a strong magnifier, you will likely see that every joint has a
dull grey dry ( american " cold " )look to it. Welcome to the world of
lead-free ...

Just as a matter of interest, what is the machine, what is the problem
that
you are trying to fix, and what soldering equipment are you trying to use
for the job ?

Arfa


Thank you very much for this reply! I knew something was up because
I've been soldering for a long time but never seen this. The unit is a
Samsung, very fancy DVD player. Sometimes it freezes so I decided to
give the main board a look. I did find what appeared to be, like you
said, cold solder joints. I guess that's not "cold" after all. Is this
lead free solder sold anywhere ?

moonlite


Well, it's sold everywhere here now, and regular leaded solder is becoming
more difficult to obtain, but I'm assuming that you are on the US side of
the Atlantic ?? The Americans, as I understand it, have not been so keen to
adopt this lead-free technology as the far east and Europe have. It's now
law here under a directive called RoHS ( Restriction of Hazardous
Substances ). The US military, for instance, flatly refuse to use it on
reliability grounds. Over here, the avionics and medical instrument
industries have been granted exemptions, and decisions on many others are
pending. Never-the-less, the far east have been manufacturing in this
technology for about 3 years or so now, so I would guess that most if not
all of the US imports of these products from the far east locations, are
built with lead-free. This being the case, I would expect that lead-free
solder would be readily available. Indeed, Sony for instance, have insisted
that their official dealers over here, use ONLY lead-free to repair ALL of
their products, for the last 2 years, irrespective of whether they were
originally built in leaded or lead-free. As you can imagine, this has gone
down like a lead ( Ha ! ) balloon in service departments ... The solder
industry itself seems unable to make up its mind as to whether mixing leaded
and unleaded solder causes a long term problem. Half say you shouldn't, half
say no problem. I recently wrote an article for a magazine on this very
subject, and took some expert advice on this point, and his reckoning was
don't mix if you don't want a long-term unstable joint.

Anyway, on your Sammy problem. It is rare for a genuine electronic fault to
be responsible for any kind of freezing. Commonly, it is caused by either a
defective / worn laser, or a mechanical issue with the laser sled transport.
As a first move, ensure that the laser moves silky smooth the whole way from
one end of its slides to the other. I had a Sammy last week that had a
tendency to freeze up about 30 - 40 minutes into a disc. The cause was
distortion of the plastic runner that one side of the laser ran on. You
could feel the laser get tight as you moved it towards the back of the deck.
This was cured by slight rubbing down of the plastic with very fine carb
paper, followed by metal polish. You can also get poor sled movement as a
result of the pinion on the sled motor splitting. If you move the laser by
hand, you get a bump-bump-bump as the pinion rotates past the split.

Sad to say though that the majority of freezing problems are down to the
laser itself. If the laser is iffy, it will have a lot more trouble reading
home-burns than commercial pressings, and will tend to freeze on them more
readily. Conversely, an audio CD will normally play faultlessly. Not an
absolutely definative test for laser condition, but usually a good
indicator.

Arfa

Arfa, I can't thank you enough for this info and for taking the time to
explain this lead-free issue. I am sure the readers of this post also
appreciate your effort!

.

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    ... solder joints on the board take solder no matter what I do. ... joints, you will need to be using using lead-free solder to rework them, ... Well, it's sold everywhere here now, and regular leaded solder is becoming ... defective / worn laser, or a mechanical issue with the laser sled transport. ...
    (sci.electronics.repair)