Safe removal of C324 & C334

[TomCrazy]

I'm wondering if you guys have any advice on how to safely remove C324 and C334 on an A600 motherboard without causing any damage whatsoever to either the keyboard connector or audio RCA jacks?

I'm working on an A600 which have lower amplitude in the sound on the left stereo channel. I have already tracked the problem down to the AC coupling cap C324, so it's definitely time to replace these two.
Only problem is, these two capacitors are fitted in an extremely tight space. As if the clearance between the capacitors and the RCA jacks is not small enough, it's even worse between the caps and the keyboard connector! It's impossible to get in with the iron there, no matter how small tip I use.

I'm wondering if it's possible to use hot air for this purpose without the plastic on the keyboard connector and the RCA connectors starting to melt before the solder does.
Anyone knows what the melting point of the plastic on these connectors are in relation to the melting point of the solder alloy used at factory? (I don't think this motherboard has been recapped.)
I'm thinking that they must have managed to do it somehow at the factory when they assembled the motherboard and the whole thing went through solder reflow, so does this mean that the plastic of the connectors are heat resistant up to at least the melting point of the solder?
Since this is a PCB from the early 90's, I hardly think they have used lead free solder which at least makes it a little bit easier. But even if I'm using proper preheating, I'm wondering if the plastic of the connectors are not going to start melting before the solder on the caps does.

Any ideas?
Thanks.

[pandy71]

If hot air is not a problem (i mean you already own hot air station which is very useful and nowadays inexpensive) - unsolder RCA then acess should be much better, all plastic parts can be saved by using adhesive, kapton or aluminium tape specially designed for soldering (heat protection - plastic melting, SMD blow off the PCB) - you should be able to bus such tape for example on ebay - just go for kapton tape such as:
Kapton Tape 15mm x 33m High temperature & Low Static | eBay or similar.

This is how industry solve problems with soldering (wave, IR, steam etc) and plastic.

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[Loedown]

The keyboard connector shroud can be removed fairly easily to give you a few more millimeters of clearance for soldering. Those caps aren't an issue for me because I have a REALLY fine tipped iron.

[demolition]

As Loedown writes, remove the shroud/head of the keyboard ribbon connector first.

Then twist off the caps using some pliers. Rotate the cap without lifting it (or you could damage the pads), and after 180-360 degrees it should come off, leaving behind the legs which should not be hard to remove one by one.

I think it will be hard to do with hot air without damaging the plastic.

[Turran]

Ive done that 4-5 Times with the tape that came with the hot air gun. The piece of tape you got from me was no good though as the glue melted on it, leaving a sticky residue.

Remove the top of the keyboard connector, tape everything and its no problem

[voyager]

Remove the top part of the keyboard connector, put some heat resisted tape (the gold one) or some aluminum foil on the connector. You can do this with a normal fine soldering iron. Use flux paste it will help a lot. You can also use hot air, again use flux. Its a nasty spot but it can be done ;-)

[TomCrazy]

Originally Posted by demolition

As Loedown writes, remove the shroud/head of the keyboard ribbon connector first.

Then twist off the caps using some pliers. Rotate the cap without lifting it (or you could damage the pads), and after 180-360 degrees it should come off, leaving behind the legs which should not be hard to remove one by one.

I think it will be hard to do with hot air without damaging the plastic.

Twist off the caps? Your suggestion suits your username pretty well.
Seriously though, I could never apply the twist method on any Amiga or any other electronic hardware for that matter. Applying mechanical force to the capacitor will also put mechanical stress on the pads - There is no way around it. It's simply the laws of physics.
I appreciate that you're trying to help, but applying mechanical force to the caps and risk damaging the pads is simply not the right way, and that is something I refuse to do.
Besides, even if I did manage to get the old caps out that way without damaging the pads, I still need to get in there with the iron when soldering the new caps into place. So using the twist method really doesn't solve the initial problem of not having that much clearance between the capacitor and the keyboard connector. But thanks anyway.


I didn't know that the keyboard connector shroud could be removed that easily. I tried it, and it came off without any problems at all. It should be a piece of cake to remove the caps and solder new ones in there with the keyboard connector shroud and the RCA jacks removed. It's kind of a pain to have to remove both RCA jacks just to replace these two capacitors, but oh well... You gotta do what you gotta do.

I have kapton tape, a hot air soldering station and all that stuff, but I think it's much safer to get in there with the iron if I can... Which I will be able to do now when the top part of the keyboard connector is removed.

Now I know what to do. Big thanks to everyone for all the advice.

[demolition]

Fair enough if you won't dare try twisting them off. I was skeptical before I tried it as well. I had an A600 with bad cap damage and the pads were coming off very easily, basically from the pressure of the iron on the solder trying to melt the solder (which was hard due to the layer of corrosion on it, despite using flux). I had a few pads come off and was annoyed having to repair it, so I decided to try the twist method, and hasn't had a single pad come off since then. Have used it on 3 Amigas by now. The pins you're breaking inside the cap are quite thin so the pads can apparently take the (mostly sideways) stress.

When you're soldering in the new audio ac-coupling caps you can move them a bit further towards the back and you should be able to reach the pad with a fine tipped iron.

[Loedown]

Twisting the caps off is still one of the safer methods available, when the pins of the capacitor become so corroded it becomes nigh on impossible to desolder them otherwise.

It's true that force is put on the pins / pads but you find that the internal connections of the capacitor give up long before the pads do, the legs either snap off cleanly at the base where they enter the capacitor or the internal connection to the capacitor internals break.

[voyager]

just use extra flux, add some solder, most of them come off, without twisting.