Lets talk about soldering...

[rudeguy]

I inherited a computer that has 10 leaky caps. Through tons of research I have figured out that replacing the caps is my best option. I know what caps I need now, what should I look for in a soldering iron? What about the sucker that everyone keeps talking about?

 

[Rubycon]

You're just replacing electrolytics?

A basic soldering station and desoldering braid will work fine.

Also see http://www.badcaps.net

 

[Jeff7]

Make sure you're getting low-ESR caps. And make sure that you've got physical clearance for the replacements.

I think the way to do it for motherboard cap replacement is:
- Get the same microfarad rating.
- Voltage rating on the new caps must be equal to or greater than that of the bad caps.

If you've not done much soldering before, maybe look into getting something like this.


I've also found that solder on commercial products seems to have a slightly higher melting point than the 60/40 tin-lead stuff I'm accustomed to working with.


For desoldering wick, I like Radio Shack's desoldering braid. I've tried a number of other brands, and it's the best I've come across.

 

[Rubycon]

Originally posted by: Jeff7

I've also found that solder on commercial products seems to have a slightly higher melting point than the 60/40 tin-lead stuff I'm accustomed to working with.

60/40? That must be a big rock you've been under!

 

[Jeff7]

Originally posted by: Rubycon
60/40? That must be a big rock you've been under!

Like I said, I like it under here.


I bought my first 1lb roll of solder back in.....um, a long time ago. Early 90s maybe. I still have quite a bit left. If I start to work on stuff that needs to be RoHS compliant, I'll look at upgrading.

 

[rudeguy]

Would a 40 watt iron be ok? I heard 60 was the minimum, but those get pricey.

 

[Rubycon]

25W is plenty.

 

[skyking]

I have a couple of computers that won't post anymore: caps are obviously toast.
I was going to take a long drive to get some lessons in replacement but it sounds easier than I first thought. I imagined all sorts of "baad things" like cooking the mobo.
Where is the best place to get caps online?

 

[Kaervak]

When replacing the caps, pay attention to the polarity. It's been a while since I've replaced any, but the negative side will be marked with a white stripe down it's side. The negative post on the board will also be marked with a white half circle. Since it's been a while if I'm wrong, someone correct me.

 

[Leros]

Originally posted by: Kaervak
When replacing the caps, pay attention to the polarity. It's been a while since I've replaced any, but the negative side will be marked with a white stripe down it's side. The negative post on the board will also be marked with a white half circle. Since it's been a while if I'm wrong, someone correct me.

Can someone explain why polarity matters?

I'm a EE student and as far as my knowledge goes, a capacitor shouldn't even have polarity.

 

[eplebnista]

Link

Electrolytic capacitors have a polarity, unlike most capacitors. This is due to the fact that the aluminum oxide is held in place by the electric field, and when reverse-biased, dissolves into the electrolyte. This allows a short circuit between the electrolyte and the aluminum. The liquid heats up and the capacitor may explode.

This is the only reason for the polarity requirement. They will behave like any other capacitor if reverse biased, up to the point that they are destroyed. Most survive fine with no DC bias or with only AC, and can even withstand a reverse bias for a period of time, but circuits should be designed so that there is not a constant reverse bias for any significant amount of time. A constant forward bias also increases the life of the capacitors.

 

[Aluvus]

Originally posted by: Leros
Can someone explain why polarity matters?

I'm a EE student and as far as my knowledge goes, a capacitor shouldn't even have polarity.

Both electrolytic and tantalum capacitors have polarity. Connecting them with reverse polarity will generally cause them to explode.

 

[rudeguy]

Originally posted by: Aluvus

Originally posted by: Leros
Can someone explain why polarity matters?

I'm a EE student and as far as my knowledge goes, a capacitor shouldn't even have polarity.

Both electrolytic and tantalum capacitors have polarity. Connecting them with reverse polarity will generally cause them to explode.

Yep. The ones I need are electrolytic. Its pretty easy to tell which side is negative.

Badcaps has been a great website for helping me figure all this out.

 

[Eli]

Originally posted by: eplebnista
Link

Electrolytic capacitors have a polarity, unlike most capacitors. This is due to the fact that the aluminum oxide is held in place by the electric field, and when reverse-biased, dissolves into the electrolyte. This allows a short circuit between the electrolyte and the aluminum. The liquid heats up and the capacitor may explode.

This is the only reason for the polarity requirement. They will behave like any other capacitor if reverse biased, up to the point that they are destroyed. Most survive fine with no DC bias or with only AC, and can even withstand a reverse bias for a period of time, but circuits should be designed so that there is not a constant reverse bias for any significant amount of time. A constant forward bias also increases the life of the capacitors.

:thumbsup:

I have a cheap 20/40W soldering station from Radio Shack. It's served me well over the years, and would work fine for replacing caps. I would use 20W.

The key to good soldering, IMO, is your tip. Not only the style, but keep it clean!

I find that tinning compound is easier than trying to tin it with solder. Get some. Clean the tip often while in use with a wet sponge, re-tinning as necessary.

If you've never soldered before, I would recommend finding something to practice on.