Recap Amiga 1200 necessary?

[Zylark]

On the one hand, if it's not broken, why fix it? On the other your A1200 is over 20 years old, and if there is one thing we know for certain regarding those little electrolytic caps inside our Amigas, it is that they will fail eventually.

Already there is a chance they've dried up some, and are leaking current. Caps are designed to do three things: store a bit of energy, block DC and let through AC. So a 'leaky' cap, one that lets DC through at low to no resistance, can at some point decide to cause a direct short to ground which spells all kinds of bad things for your system.

What is a bit annoying, is that unlike say diodes, resistors and transistors, testing caps in system is just about useless. You can only really check for direct short, and even that may give a false reading as you might pick up a signal that takes another route between your probes.

So the alternatives are to assume your caps are good for a while more at least - and change at first sign of your Amiga acting up - or play it safe and just change them now.

When changing by the way, there is no rule that says you have to change with new electrolytics. On the digital only part, Ceramics or Tantalums will last forever. For the Audio circuitry though, electrolytics or oscon caps will yield the best quality - though you could use Ceramics as well if you're not that picky about audio quality.

(One word of caution though: If using Tantalums - triple check you got the polarity right. Get it wrong and they might just explode and burst into flames...)

[Zylark]

I saw on Youtube somebody showing how he did a recapping of his A1200 and to remove the old caps he turned them a couple of times with a gripper (is that the correct word for this tool?) to remove them from the circuit board. Is this the best way to remove them?

Oh hell no, don't even try this. You are likely to tear off quite a few pads.

Best method is to have a pair of 'hot tweezers', but that is a bit specialist tool and cost a fair bit. You can use a hot-air station, but be careful. The cap may pop and you'll catch a 300'C piece of metal with your face. Also all that heating of the motherboard may cause micro-cracks in the traces. Which would be very bad news.

In preparation for my own recapping of my A4000 (still waiting for the caps, but should arrive this week), I've used an old PC motherboard to find a nice safe way to remove such caps - and not hurt the pads or the mobo.

What I've landed on is using two soldering irons as a sort of improvised hot tweezers. Both with a fairly chunky chisel type tip for max heat transfer. With an iron in each hand, each side of the cap get heated. After two-three seconds it'll begin to move, at which point one can just tip it off and away or lift off and drop somewhere.

Works a charm, and exposes the mobo to the least amount of stress both physical and from heat - and keeps the pads still very much attached to the motherboard 100% guaranteed.

[Zylark]

Here's a nice start-to-finish of (one method) replacing SM caps
 
 https://www.youtube.com/watch?v=mjCa0DAEpzQ

That video do indeed show the proper way of doing recap work. However, it is also done using quite specialist tools.

Like the hot tweezers, which your garden variety enthusiast and hobbyist have no good reason to throw money at. You can though achieve much the same effect using two soldering irons. Just make sure both can reach good temperature (at least ~350'C / 670'F) *AND* retain heat well.

I use a Hakko soldering station with a beefy chisel tip (3mm i think) and a cheap as dirt 30W 'all in one' soldering iron with a similar chisel tip. Just pre-tin the cap with a blob of solder on each side for better heat transfer, get the irons in there and see the solder melt and simply tip away the cap. Easy as icecream and 100% safe for your Amigas precious pads. Every time an Amiga pad is torn, a kitten cries! Clean the pads with a touch of flux, solder-wick to suck up the remains and then rinse the area with isoprop and a lint-free swab or tissue.

As for attaching new caps, again the video is very proper and professional. And again it is using something an enthusiast won't have just lying around usually - solder paste. solder paste is fickle stuff that cost quite a bit _and_ got an expiration date of about a year after manufacture, assuming you store it in the fridge. Solder paste is great for SMD reflow work, but to justify buying the stuff, one better do quite an amount of SMD reflow work.

Another method is to just use a bit of flux and good old solder wire. Add  a drop of flux to one pad, then place the cap the way you'd like it to go. Keep in mind that electrolytics are polarized, so it do matter which way round they are attached.

Anyhow, with the cap in place and the drop of flux on the one pad, melt a little solder on the tip of your iron to create a tiny blob of solder on it. Now use this blob to 'tack' on the cap on the side where you applied the flux whilst you hold down the cap with some tweezers or similar so that it do not move about. Once done, clean the tip, and solder on the other side properly. Then move to solder on the first side properly. And done.

Next cap please!

[Zylark]

Just found something on the internet. It's a SMD tweezer soldering iron:

SMD tweezer

It's affordable but will it work?

Or this one?

They both seem a bit anemic. The top one only 20W per element, and the bottom one a smidge better at 25W. Add to that the rather thin tips, and you have pretty poor heating power coupled with pretty poor heat mass and heat transfer surface.

They may be perfect for lifting off small components such as resistors and ceramic/tantalum caps. But the electrolytic SMD caps have significantly more heat absorption mass. Maybe even so much that those hot tweezers will either struggle or fail at removing them altogether.

Have you looked into getting some quick chip solder? With it you can lift off SMD components using just a (good) soldering iron. Cheaper than hot tweezers too. Or, do as I do, use two soldering irons.