Soldering iron safe for M/B repair?

E

[evo]

Gawd
Joined
Dec 4, 2000
Messages
818
one of my friends just gave me an Asus a7n8x-e that is brand new which he somehow managed to knock a capacitor off while installing. I have the cap and know where it's from so I'm hoping I can fix a new one back on there and have the board work. There are no IC's around it, but I'd still like to use a low enough heat to be sure that it doesnt damage the board further...what sort of wattage/tip should I be looking for? Also, anyone know which side +/- should be which in the board? One half is shaded the other not, no +/- markings...


Thanks :)
 
Not too sure on what type of soldering iron, should be low enough to just melt the solder and put it on the board. Check the other capacitors and see the way that they are set up for positive/negative
 
Actually, the replacement cap should be "Low ESR" or "Low Impedance"

Try Digikey or Mouser.

Ironically, you need some power to melt the solder "rivet" that goes thru the 6-layer (usually, sometimes 4-layer if older) circuit board. If you have to solder onto a ground plane (solid sheet or copper on the back side) you will need even more power.

Getting the solder out of the rivet is also challenge. Usually a high quality solder wick is the best method.

I have successfully re-capped 2 mobos and I wouldn't consider the job w/o a stereo microscope. However, if you have really good eyes and can focus about 2-3" in front of your nose, you may be able to do it. Get some x-tra strong reading glasses as a minimum if you have good eyes.

My guess is about a 35w iron where you will have to shape the tip into a small "screw-driver" or chisel tip.

See if you can practice on a junk board. If you have a local computer shop, they may have some scrap to give you to practice on. This is probably the best thing you can do.
 
If you have a temp-controlled soldering iron, you can get SMT tips that are small and conical, designed for this. I have two SMT tips for my Loner 971 iron, one is straight, and one is bent to allow for reaching into small spots.

I haven't done this though. I'd recommend having a solder wick, desoldering braid, or a desoldering station to get rid of what's currently there. I'd also recommend a good medical-grade tweezers for holding the cap in place, and a magnifying lamp. Someone online should be able to tell you the lowest temperature that will do a good job; the lowest temp that you can get away with would be good so you don't damage any traces.
 
MrCreosote said:
My guess is about a 35w iron where you will have to shape the tip into a small "screw-driver" or chisel tip.
Click to expand...

Don't file it down or "shape" the tip. You will ruin it, since it's not one solid metal that makes up the tip.
 
I have had the best luck resoldering motherboards with the hottest iron I had available. (100W weller station)

The trick with a very hot iron is to minimize the time that the iron is in contact with the board.. with a "cooler" iron you are keeping it in contact with the board so long that the heat gets everywhere and damages it. (killed a board with a 25w iron)

==>Lazn
 
Lazn_Work said:
I have had the best luck resoldering motherboards with the hottest iron I had available. (100W weller station)

The trick with a very hot iron is to minimize the time that the iron is in contact with the board.. with a "cooler" iron you are keeping it in contact with the board so long that the heat gets everywhere and damages it. (killed a board with a 25w iron)

==>Lazn
Click to expand...

QFT.
 
MrCreosote said:
Actually, the replacement cap should be "Low ESR" or "Low Impedance"

Try Digikey or Mouser.

Ironically, you need some power to melt the solder "rivet" that goes thru the 6-layer (usually, sometimes 4-layer if older) circuit board. If you have to solder onto a ground plane (solid sheet or copper on the back side) you will need even more power.

Getting the solder out of the rivet is also challenge. Usually a high quality solder wick is the best method.

I have successfully re-capped 2 mobos and I wouldn't consider the job w/o a stereo microscope. However, if you have really good eyes and can focus about 2-3" in front of your nose, you may be able to do it. Get some x-tra strong reading glasses as a minimum if you have good eyes.

My guess is about a 35w iron where you will have to shape the tip into a small "screw-driver" or chisel tip.

See if you can practice on a junk board. If you have a local computer shop, they may have some scrap to give you to practice on. This is probably the best thing you can do.
Click to expand...

this may be slightly off topic but dont low impedence caps have a high ripple current and low esr caps have a low ripple current? i thought low ripple current was the most important aspect of caps for mb mods/repairs. if low impedence caps are good for MBs it makes my life alot easier seeing as finding low esr caps in speciffic values is next to impossible.
 
low ESR -v- low impedance:

I you go to Nichicons sight and look at their technical information, they give a nice plot that shows the relationship between these two characteristics.

The impedance curve is a smooth concave curve with its highest values at its lowest and highest frequencies. The middle of the impedance curve actually coincides with the ESR curve. However, once you get towards frequency extremes, the impedance curve asymptotically approaches Xc (series capacitance) at lower freqs and XL (series inductance) at higher frequencies.

In other words a low Z cap must have low ESR because they are the same value.

Be sure to get Long Life caps which are rated 4000 to 10000 hours. Of course this is at their rated values and longer if not loaded as much.

I have used Nichicon UHE or HE.

If you want to read about something amazing, do a search on "motherboard bad capacitors" and you will learn about an amazing industrial espionage blunder in Tiawan!
____________

most cheap soldering irons have copper tips you can shape anyway you want.

yes, too much heat is actually not bad so long as you know when to pull the iron off the circuit. It can be quite amazing how much heat is needed to desolder a 6 layer rivet thru a ground plane.
 
You must log in or register to reply here.
Back
Top