Advice on Lisa 2 restoration

On 04/04/11 12:55, Steven Hirsch wrote: Well, it'd be worth a shot. The thing about a preheater is that it has a much larger surface area -- so instead of heating a small patch of board (which is what the hot-air gun is for) it'll bring the whole board (or a large section of it) up to a given temperature. The idea being that instead of having to bring every pin on the chip 250C. Less energy required, faster time-to-melt, and as a result less damage to the PCB. Usually the solder joints will stay hot for a little longer too -- meaning you get a few extra seconds to vacuum-pick the part off of the board. Well, that ties in with my experience with the Aoyue one (basically a clone of one of the Hakko workstation-type vacuum solder suckers). I would have thought the OKI one would have been pretty decent though... weren't they Metcal at one point? I suspect the reason that trick works is the flux -- you add extra flux, which helps to remove oxidised solder. The bit of extra solder improves the thermal coupling between soldering iron tip and joint. Yes -- exactly right. You cut the pins off with flush-cutters -- these are the very small wire-nippers that you usually use to cut component pins flush to a solder joint, not the massive (by comparison) side-cutters usually used for cutting wire and cable. Cut the pins and remove as much of the connector frame as possible. I usually use a Dremel and a selection of cutting/grinding bits to go most of the way through, then finish off with hand tools -- needle files and maybe a junior hacksaw blade. Desolder the pins and pull them out, the holes will be filled with solder. Put some flux on the joint, and a drop of solder on your iron tip. Apply to the joint and melt in some fresh solder until you get a convex bubble on both sides. Use desolder wick to remove this -- sometimes you can push a little bit of the wick into the hole, which helps A LOT when wicking solder out of holes. If the hole won't clear after two or three tries at this, remove all the solder you can, then heat a piece of tinned copper wire alongside the joint, like this: wire | ## soldering iron tip | ## |## =============== board Push the wire through the hole while heating it. Again: fresh solder and flux are VERY useful. If it won't go through from one side, try the other side. When the wire goes through, start moving it up and down, and remove the soldering iron. The motion prevents the solder from sticking to the wire. You should now have a clean (or close enough) hole which you can push a new part lead through (and solder it). I've got a box full of the things... only problem with carbide bits is that they break if you look at them funny. Any decent supplier should have it. Farnell stock the 3M stuff, but it's unbelievably expensive (?30 a roll). Their own-brand version ("Multicomp") is about a third of the price. I honestly can't remember if you get 10m or 25m on a roll... but it lasts ages. Just don't let the kids near it! Either the 12.7mm (1/2in) or 18mm wide tape is fine for most things. The thinner stuff (1/4in) is better if you're going to be taping down wires and nothing else... -- Phil. classiccmp at philpem.me.uk http://www.philpem.me.uk/