Best capacitors to use for se/30 recap ?

[srieck]

I know I need 10 x 47uf (16v) and 1 x 1uf (50v) -

What are the most reliable type to get ? (from digikey I assume)

Do I need a particularly hot soldering iron? (I just recapped my inlaws iMac G5 and that was no ordinary solder! Very tough to melt. Is the se/30 board going to be similar? Is a regular 40 watt iron enough ?)

 

[srieck]

And also does anyone have any reasons why this method is good or bad?

http://inbox.apana.org.au/?p=1342

 

[protocol7]

I've been looking at different solutions too as I gradually build up the courage to tackle recapping my Classic II.

Twisting off the old capacitors sounds easy but I wonder what the chances would be of lifting a solder pad as a result? While cutting the capacitor is more work, it seems like it would put less stress on the pads.

Also, are newer electrolytic caps less prone to leakage? They would probably be easier to hold in-place while soldering than the tiny tantalum ones, but if there's a chance of them leaking further down the road, then it seems kinds pointless. The tantalums seem to be the tidiest option.

 

[srieck]

I did just try the twist method he describes on an old circuit board. It worked well. I don't think I messed up any pads.

Since it's right down the street, I have to ask...are radio shack caps frowned upon? Or are all of these electrolytic caps basically the same?

 

[srieck]

I think what I just learned was that the secret to twisting them off is to not apply any up/down pressure. Just an even slow steady counterclockwise twist.

 

[srieck]

...and another thing - why is it not recommended to heat up the leads on the back side of the board and just pull the whole cap with leads out?

 

[srieck]

...and another thing - why is it not recommended to heat up the leads on the back side of the board and just pull the whole cap with leads out?

 

[tt]

For a suggestion how to remove the caps, look here: viewtopic.php?f=7&t=15627

Despite the excellent documentation on the OP's first link, I think the caps used were not the best choice. Use SMT components for an SMT designed board. Using larger through-hole components is asking for mechanical assembly and handling damage.

 

[Unknown_K]

The problem with heating the leads from the rear while pulling the capacitor out the other side is that if the solder cools while you are yanking (or something is stuck to the leads that is bigger then the hole) you have a good chance of pulling out the metal layer in the circuit board itself. Boards can be multi layer with circuit connections in multiple layers while the hole is plated at the factory. If you damage that connection there is no real way to fix it.

 

[srieck]

Very good to know. So is it best to twist them off gently or clip them off with a wire cutter by essentially chopping them apart which sounds like it would leak corrosive goo?

 

[jsarchibald]

My way is probably frowned upon, but I got a dozen cheap emacs that all had capacitor issues. I put my finger on them, and with a gentle circular motion, found that they came out quite easy. I used a very fine drill to get the hole back the way it should be, and re-capped. Worked a treat!

 

[protocol7]

srieck, did you find that if you twisted them gently without applying up or down pressure that you could remove them every time without lifting the solder pads? I'd just like to know how reliable/safe this method is vs cutting them up with a wire cutters.

The cutting method shouldn't leak electrolyte if you do it right as it essentially pinches the cut capacitor shut. In any case, if they have already leaked you will need to wash the board anyway, so a little more spillage is probably not so bad.

 

[srieck]

Actually there were about 12 on an old cd circuit board...all came off relatively easily and no pads were damaged.

Still I'd recommend trying it out on something you can trash.

 

[gubbish]

I used the twisty method when recapping my SE/30, and I agree - it worked well, with no lifted pads. Just gentle motions and they come off easily.

 

[phreakout]

Okay. Twisting SMT (surface mount) capacitors to get them removed is very risky. You can end up not only lifting the pad but also ripping the pad and trace along with it. Then you'll have no other choice but to repair the entire connection, and that isn't easy. This would involve sitting down with a pad of paper and a multimeter with continuity tester to trace out the circuit path. Then you'd have to solder a very thin wire (enamel coated or similar) from the origin to the destination, creating a bypass. Sometimes you can't make connection from the top or you'll end up tracing to underneath the logic board.

These are reasons why I don't recommend it. If you want to do it the safe way, just use 2 pencil soldering irons of the same watt value to melt both ends of the SMT's contacts. Then, when the solder is melted enough, simply lift the part out and away using the iron's tips like a tweezer. I'd recommend no more than 40 watts of power for the irons and make sure they have a small diameter, fine tipped tips.

While you can use electrolytic caps to recap a board, remember that you might have to go through the recapping procedure again in 10 to 15 years. If you use Tantalum SMT caps (like what 68kmla member Trag sells), you are given a much longer lifespan out of the job done.

I do SE/30 board recaps from time to time and I follow the above method as I did the research. It's a little extra work, but it is much more safe and more successful at getting this done.

73s de Phreakout. :rambo:

 

[srieck]

Well the deed is half done ... I got all 11 of them out and as my luck (or lack of skill) would have it, I actually did manage to rip out one pad :disapprove: ...the one for C5 (negative). The rest are intact and look pretty good.

I managed to clean it all up figuring it was hopeless when I noticed the tiny sliver dot through the hole in the board where the pad for C5 (neg) attaches. Again, I cleaned it out and grabbed a small piece of very thin, hard wire my wife uses for beading bracelets and stuff....I tinned one end of the wire with solder, popped it in the hole and heated up the wire with the iron. It was a perfect fit and held tight onto the dot...So I'm HOPING I've made a decent contact with which to connect C5 (neg).

 

[srieck]

So the board is in an antistatic bag while I wait on new caps in the mail...

Place your bets here.

 

[srieck]

I don't trust my ability to do surface mount...but replacing with standard electrolytics might mean replacing down the road.

So what are these ? And would they do the Job...(I know C6 is 1uf 50v)

http://cgi.ebay.com/25-AVX-TAP476M016FCS-TANTALUM-CAPACITORS-47UF-16V-20-/320679368164?pt=LH_DefaultDomain_0&hash=item4aa9fad5e4#ht_2567wt_907

 

[trag]

It is easier to solder surface mount into place than it is to solder leads onto surface mount pads. The leads will try to wander all over the place with the weight of the cap pulling them this way and that. It's very difficult to get a good lead-to-pad connection.

To replace a surface mount cap (or other component):

1) Remove all the old solder from the pads so that they are flat and level with the board.

2) Clean the board with isopropyl alcohol or similar to remove all the old solder flux and other detritus from the board.

3) Tin just one pad for each capacitor. Tinning means put a little solder on the pad so that there's just a tiny hump of solder on the pad.

4) Using tweezers, place a surface mount capacitor on the pads. Take a flat blade screwdriver (or similar) and gently press down on the center of the cap. Remove the tweezers, while continuing to press with the screwdriver.

5) While still pressing with the screwdriver, use a soldering pencil to melt the solder on the tinned pad. The cap should sink a little on that end as the solder on the tinned pad melts.

6) Make sure you evenly heat the pad, the cap terminal and the solder. When all three are thoroughly heated, remove the soldering pencil.

7) Wait a few seconds, then remove the screwdriver.

8) The hard part is done, the cap is firmly in place. Now use standard soldering technique to solder the unsoldered pad/terminal and touch up the tinned side if necessary.

Size D caps which replace the electrolytic SM caps really aren't that small. There are some good photos over on the Wiki.