Desoldering SMT Chips?

From experience, these are likely to be line out buffer amps, but I would have said that it is unlikely that both or even one of them is faulty, unless something nasty has been done on the jack side of things. I would have thought that the most likely suspects are that the analogue sound has been disabled or muted somewhere in software, or that a supply rail to the opamps has gone missing, often due to a short circuit decoupling electrolytic somewhere. I get faults like this on various manufacturer's items on a regular basis, and SM chips are, on the whole, pretty reliable. This exact symptom was very common a couple of years back, on a particular Toshiba DVD chassis, and was caused by a short circuit cap. It's also very easy to accidentally turn off the PCM analogue mixdown to the line out sockets via one of the menus, often several layers down in the "Audio Setup" menu suite.

If it's definitely not a 'soft' issue, you should first 'scope the inputs to the chips, and analyze the DC conditions on their pins, but if you do need to ultimately get them out, there are several ways. With a little 8-pin, my preferred way is to use an 8-pin-shaped bit on my Antex temp controlled station. That unsolders all 8 pins at once. Flood the pins with new solder first, and before Smitty says so, add a little liquid flux to the equation !! ;~} The Antex bit with a long sloping edge does a pretty good job too, but only one side of 4 pins a a time. My next method is to flood the pins with new solder, then wick it all off with new, good quality soldamop. I then slide a piece of thin wire like rework wire or wirewrap wire under all the pins on one side, and anchor its end by touch soldering to any convenient joint. It is then just a case of pulling firmly away, and slightly up from, the pins with the free end, whilst touching each pin in turn with the tip of a fairly hot iron. Each one will pop up from the board, and the wire will pass under the pin at the same time, removing any remnants of solder. Be careful that the last pin to be left attached, doesn't twist, taking the pad with it.

After that method, the final one is by using hot air. There are good people on here who swear by all sorts of ways of doing this using paint stripper guns and the like, but I've always found that this is tricky for the amateur, and is best done with a proper hot-air rework station.

To solder in new ICs, make sure first that the pads are wicked absolutely flat, then carefully position the new chip ( right way round of course ). Whilst holding down the centre of the chip, touch one corner pin with a fairly hot iron. The remnants of solder on the pad, and the tinning on the leg, will normally be enough to tack it in place. Recheck the positioning of the other legs, then tack the opposite corner. Now add some liquid flux, and go ahead and solder normally. Don't worry if the solder 'blobs' between a couple of pins here and there at this point, but the liquid flux will go a long way to preventing this. When all pins have been soldered, check with a magnifying glass, and remove any solder shorts with a hot iron and thin gauge soldamop, applied to the vertical faces of any affected pins. Recheck that you've removed the blob, whilst still leaving a fillet of solder between the pad and the pin. Removal and refitting is not hard at this level - it just needs a bit of care. If you have some scrap boards around, practice first.

Arfa

For small chips like that, you can remove them easily using a regular soldering iron. One method I use is to apply a blob of solder to all

4 pins on one side. This will allow you to melt the solder on those 4 pins at the same time so you can lift up that side. Remove the solder from the lifted side with solder wick and then repeat on the other side.

An alternate method is to simply cut the pins with a sharp blade, then remove them from the board with solder wick. Be careful not to cut into the board traces.

Note that the chip is probably glued to the board, so it will take some force to remove it. Practice on a junk board if you can.

Having said that, I doubt this is your problem. Op-amps are very reliable. Andy Cuffe

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steve

No it will not. I wish you guys would quit buying that junk -- and even buy a good used unit -- for the same price -- you se them on eBay (and let quality go to trash!)

If you don't mind a little homebrewing, consider building an SMT hot air pencil; here is my version:

Regards,

Michael

msg wrote in news: snipped-for-privacy@corp.supernews.com:

or unsolder one leg at a time. Heat each leg with a soldering iron, and lift the leg with tweezers. For the last two or three just heat and lift the part...

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me wrote in news:Xns995589828BEFmeherenet@38.119.71.210:

Hard to do with surface mount technology. No legs to lift.

And the pads are CLOSE together.

BTW, thanks to MSG for the cool idea of converting a cheap soldering iron to into a hot air device, and the well written description of how to do it, step by step.

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