Capacitor replacement

[trag]

before you replace *all* the caps, see if any leaks exist (easily found by smell or if the solder around the caps isn't shiny, but very dull, or even yellow or green), and if they do you'd better clean them up with PCB cleaner or 99% pure alcohol, because they will corrode the board and traces and eventually no matter how much cap replacement you do, it will never work again!

What he said, except the part about it never working again.

This thread has been focused on soldering, so the following wasn't really topical, but it probably needs to be said, in case someone reads this thread without reading some of the other cap replacement threads.

A cap replacement job has three basic steps:

1) Remove the old caps

2) Clean the board. This includes use of solvent and/or detergent to remove all the residue which may have been left by leaking capacitors.

3) Replace the caps with new ones. Tantalum replacements will not leak later.

If you don't clean the board, the electrolyte which has leaked onto the board will continue to corrode any metal parts it touches.

An example of the damage leaking caps can do was my old IIci board. One day around 1995 it just wouldn't power up any more. It turns out that the caps leaked onto the board, But the caps weren't content with no longer doing their job. The leaked fluid corroded away the solder connection to some component pins and more importantly actually ate the solder and copper out of one of the vias (hole) in teh circuit board.

That copper/solder filled hole was meant to connect a trace from the front of the board with the back of the board and now that connection was gone.

So, using my DMM (as mentioned by an earlier poster) I traced the connections forward and back from the damaged point. Once I found accessible points forwards and backwards of the damage, I ran a wire between the two points and soldered it at either end. Voila, board repaired. BTW wire wrap is very good for this kind of thing and available in small spools from Radio Shack.

The damage done by capacitor electrolyte can be very difficult to detect visually. A good 5X or 10X magnifier can be handy. Corroded contacts may look fine until you poke at them with a (e..g) dental probe and find that the metal is no longer solid.

This corrosive effect is why it is soooo important to replace those old caps at the first opportunity. They can destroy your board.

All that said, I haven't replaced all the ones on my old boards yet. There's just never enough time for all the projects. Any day, I'm going to order those two reels of tantalum caps and start replacing...

 

[JDW]

I fully agree with Trag's advice and can only supplement it by stating what I have said many times before: use the continuity check feature of your DMM to check trace integrity if your board isn't working right after you've changed the caps.

As for da9000's "God of perfection" remark, I can only say that I have replaced all the caps at once on two SE/30 boards without problem, and I do not have a Heavenly abode (not yet anyway). That doesn't mean one should not take care when doing a cap job. Indeed, I have mentioned that before when people say they don't have a tweezer style soldering tip (which I do have). Breaking traces is possible. But it's also not the end of the world. Again, use the continuity check feature of your DMM on the traces that attach to both sides of each cap, and trace them back to their origins. That's what I do to ensure a 100% fault proof cap job. Again, this is not "speculation." I've done two boards as have others on this site. Take care, but don't avoid doing the cap job. Most all SE/30's need to have a cap job done now as most of those SMD electrolytics have leaked (whether you can see the leakage or not).

 

[equant]

tweezer style soldering tip

Can you provide a link to what this is? I'm not positive what it is you're using.

Thanks

 

[JDW]

We have a ESA-safe HAKKO 937 soldering station here at work, used to make prototype electronic devices and for product repairs. The tip I spoke of is the HAKKO 950 Hot Tweezer. Both sides of the tip are changeable and we have a kit of various widths that make it easy to desolder SMD components of almost any size, including the SMD caps used on the SE/30 logic board. While this may be overkill for personal or hobby use, I highly recommend it if you happen to be a bit wealthy 8-o or very serious about soldering! It's not THAT expensive though. Just compare it with the price of an oscilloscope and it will look dirt cheap!

No doubt, some will contend (as many have in the past on this site) that the desoldering job can also be done with two $9 soldering irons placed on either side of the cap. I agree that such is possible. But I myself don't go that route because, well, I have a HAKKO 937 and 950 here at work! And honestly, a professional device makes the job faster, safer and cleaner.

 

[equant]

Thanks for the link. Looks very nice. The dual soldering iron method sounds tricky as well. Am I the only person that uses desoldering wicks? Would that be a bad idea when doing a cap replacement?

 

[JDW]

There are not a lot of "bad ideas" in terms of desoldering because there are many ways to attack the problem. But some means of attacking the problem (capacitor replacement) are better suited to some than others. Some methods require more patience and skill than others. Although I have an EE degree and have years of soldering experience, I still prefer pro tools to make my job easier and ensure the job is professional and quite nearly "perfect."

Just don't scratch your board, which could brake a trace. That could happen if you apply too much pressure to a normal soldering iron (or two, one in each hand), and your hand slips and a sharp iron tip sinks into your board and digs a 4cm trench in it! I've seen this happen!

Don't apply too much heat. With a professional tool you can adjust the heat, but with a $9 iron, you cannot. But if you buy a low wattage iron (around 25W) it may not provide enough heat so you may hold it on the board too long and over heat some parts. There is a lot that can be said about this point, but it's too much for me to write here. Suffice it to say, you need to apply "the right amount" of heat to melt the solder and remove the component.

Solder braids or wicks will help this sometimes, but you can't always pull all the solder away from SMD components this way (I know this firsthand), and sometimes you will get frustrated and yank on the SMD part and brake a pad and/or trace. With my HAKKO tweezer this never happens because I am not interested in cleaning up the solder and then pulling on the part. With the tweezer, I heat the solder to melt it on both sides of the part and then easily pull off the part. It works well, without any desoldering braids or pumps.

Anyway, you need to desolder all your caps (making sure you first have the new caps handly), then clean the board with something like 99.5% pure dehyrated Ethanol alcohol (I advise against "rubbing" alcohol), then solder in your new caps. (Sorry for the Japanese link, but I live in Japan and source my Ethanol here too.)

Now I have long contended, and still do, that you should replace all the caps, including the two axial caps, in one fell swoop. While others may say you can see or smell leaked fluid, I for one cannot. I tried easy method once (replacing only the caps around which I physically could see leaked fluid). That didn't solve my problem. I then replaced all the caps and the problem went away. And since most of these electrolytics contain fluid, and since many have leaked, and since all will leak at some point, why NOT do all of them at once! Because if you only do a few, what if you get a system crash now and then you cannot explain? There will always be the possibility that you didn't replace one or more caps that you should have. So I strongly recommended doing the ENTIRE BOARD, SMD caps and the two axials too.

Lastly, while I am by no means an "expert" on SE/30 repairs, if you wish to read much more on this subject, you can just search this site for "caps" or "capacitors" or "Ethanol" along with "JDW". You can Google for that too, as I am known as JDW on most other classic Mac sites, and I have written many of the same words over and over and over again on many sites. Some threads contain more detail the use of Ethanol as opposed to other cleaning methods, other threads talk more about types of capacitors to use a replacements, etc. Just do a little searching with "JDW" as a keyword and you're bound to find a wealth of information. And no, this is not a plug for me. I simply like to participate in these discussions to see what others have done and to share my own experience to help others avoid the same pitfalls that affected me when I first started out.

 

[da9000]

@trag:

I stand corrected about the "never again". I'm an optimist, what was I thinking!!! ) ))

Also thank you for writing out so clearly what electrolyte does to the boards. That's what I was obviously getting at.

BTW, what recommendation would you make for a 5x+ magnifier?

@JDW:

When I mentioned replacing components all at once, I meant *all* motherboard components I'd wager a big bill on most people not getting it right the first time when there are 100+ components. Anyways, don't mean to be argumentative, just naming realities and probabilities.

As for your methodologies and using the DMM, I totally agree and practice the same. No sense in not checking your work before firing up the machine. Always double + triple check your work, and like mentioned earlier, it will also avoid exploding (tantalums!) capacitors.

BTW, have you found a similar Ethanol product in the US that you can recommend? If not, don't worry.

@equant:

I use desoldering wicks! Well, not all the time. One of the problems with them is picking the right granularity. If it's too coarse, it won't suck small solder joints and small gobs of solder. Perhaps a worse thing about wick is the fact that it damages the tip of your iron, by scratching the nickel (?) plating, and thus making your iron less useful over time. Lastly, it also runs out, and quick if you're replacing 16x20pin chips

Happy desoldering everyone!

 

[JDW]

have you found a similar Ethanol product in the US that you can recommend?

I've spent the past 14 years in Japan. So I can only say what I use, which is a Japanese product available only here in Japan from a Japanese supplier. No doubt there are places in the US where you can buy it. But I wouldn't know where. Also, I've heard from others that it's "hard to find" in the US, but I don't know what that means. I can only assume it means that some restrictions may be placed on it in the US. But it's easy to find here in Japan, perhaps in part due to the fact that the Japanese don't get their jollies off drinking what should otherwise be a cleaning agent! 8-o

 

[da9000]

Hahahaha, yeah, I'd rather drink cheap beer!

Oh well.