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soldering dry joints on laptop power board


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#1
digikiwi

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I have a problem with my laptop which appears to be a common design flaw as documented in the link below.

http://www.geekstogo...00-t117898.html

Now, I've done some basic soldering, 3.5mm headphone plugs and the like, but this is a whole new ballgame.

SO with no little self interest I thought it might be good to start a thread on solder-repairing dry joints.

Have you done it?
What successes have you had?
What mistakes have you made that others should avoid?
What tips would you recommend?

How can you get better?
How can you prepare for the job, and work up the requisite skills?

Hopefully your comments will help people like me making the right choice on whether to try it themselves.

Digikiwi

Edited by digikiwi, 25 June 2006 - 04:24 AM.

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#2
SRX660

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I have been replacing the caps on older motherboards. A very good idea i found to clean the connections of excess solder is here.

http://www.usbmicro....5FDFF29EA1.html

I also use a high wattage 60 watt pencil iron to heat the area up faster. The 12 to 25 watt irons can take a long time to heat an area up and could cause nearby damage by heating up so slowly.

http://www.action-el...eller.htm#Irons

One problem i have had with some caps is that replacing the Choyo 1000uf 25 v caps with nichicon ones is that the nichicon are about 1/3 larger in diameter than the choyo's. In some close quarters they will not fit in place. By leaving the connections long and bending the caps outward so they all will fit. It looks funny because they stick up quite a ways from the MB but so far does work.

heres a list of cap manufacturers and what they have.

The lower the ESR, the higher the grade. (In the following table, the lower a capacitor is placed, the lower the ESR, the higher the grade.)
Nichicon NCC Rubycon SANYO Remarks
VZ KMG YXA MV-CZ 105C General Purpose
PW LXZ - MV-CX Miniature, Low ESR
HE KY YXG MV-CA K6, K6-2, P2, P3 grade
HD KZE ZL MV-WX K7, P3 grade
HV KZH ZLH - Extra long life, miniature, Low ESR
HM KZG MBZ MV-WG K7, K8, P4, P4+ high quality grade
HN KZJ MCZ - Ultra Low ESR
HZ - - - Lowest ESR of all electrolyte capacitors

I'll try to add more to this as i remember them. These just come to mind because i'm doing the cap thing quite often.

SRX660
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#3
Kemasa

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I have not heard the term "dry" solder joint, but I suspect the correct term is "cold", which is where not enough heat was used and/or the solder was moved while cooling.

I have made such repairs and have been successful, but I have also done a lot of soldering. If you want to get good a soldering, you need to practice a lot. I soldered the main board for an 18 slot S100 machine, so there was lots of soldering, including all the pull up and pull down resistors.

I would be very careful using higher wattage soldering irons as too much heat will damage things. If you melt some solder on the iron before trying to melt the solder on the board, it will help to reduce the time. You can also get small heat sink clamps to protect parts.

You need to use the correct tip for what you are doing. A fine tip is needed for small areas, but a wider tip is needed if there is a larger area and the wider tip will help to spread the heat faster. If you are removing parts, you need a de-soldering tool to suck the solder up, making it much easier to remove the part quicker.

In general, you should not hold the soldering iron on the part for any extended period of time, with the exception of heavy parts/wires.
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#4
digikiwi

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Thanks for your replies. I hope I don't need to solder and will try a couple of other options first. If I do I will need to invest in a better soldering iron.

Gas powered or electric ?

Kemasa, re "dry" solder joint - I think the author I picked this up from meant not enough solder present for sustained functionality which matches up with "solder moving before cooling", but I'm in no position to quibble over semantics :whistling:

Digikiwi
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#5
HaraldR

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My 2 cents worth

Re "dry joints"

As a technician (over 35 years), dry joints have been the scourge of many a fault finding.

A dry joint is caused by applying heat from above work,the Solder melts on cold surface.
using a "cold" iron (not to operating temperature)
using an tip too small or unsuitable to job at hand.
Dry joints cause resistive connections,frying (voltage arcing in joint),noise

The "best" solder joint is the one you can't see.

Digikiwi:the gas irons are great but not for pc work

Use De-soldering Braid or wickas it causes less damage to circuitboards.

A solder vac(uses suction to remove solder) is another must have.

If you are serious about soldering PC boards then a solder stationis a must.

If you must use a soldering iron then a thermistaticly controlled tip is essential.

Edited by HaraldR, 26 June 2006 - 10:30 PM.

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#6
Kemasa

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What you call "dry", I call "cold" :-). Just a difference in terms. I am not sure of why it would be called dry, since as you describe it the issue is "cold" :-).

I agree with having the proper equipment. I personally don't care much for the wick and use a suction device instead, but there are times which that would not work as well.
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#7
digikiwi

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Digikiwi:the gas irons are great but not for pc work


Why are gas soldering irons less suitable for computer work - is it the ability to maintain constant temperature.



A dry joint is caused by applying heat from above work,the Solder melts on cold surface


So the answer is to briefly preheat all surfaces the solder is top adhere to? As far as "from above" goes, should you try to not work with the tip downwards but in a horizontal fashion.


Thanks for all the comments so far- I've already learned heaps without having to burn my fingers, not to mention my wallet :whistling: - please keep them coming.

Digikiwi
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#8
HaraldR

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Gas irons (I have the Portasol and the weller super pro).
Both are teriffic for general soldering cable distribution frames,twist joints,audio connections,car electrical and some pc work,heat shrinking,the control over temperature is not precise and they vent an enormous amout of heat from the side of the tip,easily burns components in close proximity and the occasional piece of furnature or body part (whoops) :blink :) : .I certainly would not attack a Motherboard with one. :help:

The portasol was banned at work because it reported to have a tendancy to explode.
I have had at least 6 since 84-5 and never had a problem,apart from losing them. :whistling:

the Correct method is apply iron from under work pre heat work touch solder to work capillery flow the solder melts and blends both connections with a fine film of solder, :blink: A great lump of solder does not mean the connection is better in fact quite the reverse.

I know you can't solder a pc board from below,no but it is a technique, whereby you apply iron to work a moment prior to touching solder to the union where the irons tip contacts the work.
you use a much finer guage of solder. :woot:

Edited by HaraldR, 26 June 2006 - 10:31 PM.

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