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michael8554

Surface Mounted Chip Replacement?

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Looking for a UK company that has the expertise and equipment to replace a faulty 16-pin Surface Mounted MAX232 chip. 


About 10 years ago I managed to solder hair-thin wires onto a Philips Toucam for the long exposure mod, but that was a £30 item, not a board that costs £250 to replace if I screw up.


Michael

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Hi Michael, it's not impossible to do it yourself. The Max232 is a fairly hefty chip by SMT standards.

Get a decent soldering iron. Apply extra solder along the whole line of pins on each side. This will hold more heat, keeping the solder melted longer. Use 60/40 leaded solder as this melts at a lower temperature and will make the lead free (that may be there already) melt easier too.

Use a fine-tipped screwdriver to put GENTLE raising force on end of one row of pins.

Apply the iron and move it back and forth until the chip lifts a little. Repeat moving the screwdriver around the corners of the chip until it comes free. Do not over force it or the tracks will lift.

A pro would use a big shaped copper bit that heats all 16 pins at once.

Alternative method I have used for a big chip - carefully cut all the pins with a dremel and a narrow cut off wheel. desolder each pin individually.

Once clear, clean up the pads with desolder braid, then with a fine tip tin each pad with a small amount of solder.

Place the new chip in place (the right way round, don't ask!)

Using the fine tip just press each pin down onto its pad, you will feel it 'give' as the solder melts. The chip will be left a bit 'proud' but it will work fine. I have soldered chips with 30+ 0.5mm pitch pins this way.

Edit - another way is to make a sheet metal shroud that just leaves the Max 232 exposed and use a hot air gun to melt the solder and lift off the chip. My stepson 'reflowed' a major chip on a playstation this way that had broken away from its pads.

Edited by Stub Mandrel

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Thanks Stub

Part of the reason I'm hesitating on this is recent experience replacing popped electrolytics on a PC motherboard.
My soldering iron is powerful enough to do jobs like fitting a new 5.5x2.5 power plug, but after snipping the electrolytics off of their legs, it failed to melt the solder on any of the remaining legs.
So a hotter more concentrated approach was needed, with the risk of damaging the track and adjacent components.
Though your idea of the hot-air gun is appealing - do they really get that hot, 60/40 melts at 188C/370F?
Michael

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What's your location Michael ? I know a place in S London that will do it while you wait.

Some vids on YT  on replacing SMDs.

Dave

Edited by Davey-T

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Looked at the videos on YT

The first one had about the same packing density of my board

Wasn't impressed with the heat that was getting to adjacent electrolytics, given my experience above of dried out electrolytics - maybe a metal shield like Stub suggested.

But was impressed how brutal they were with the solder and iron, and how cleanly the chips came off, I thought that extra added solder would be everywhere.

Michael

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There are several issues with removing surface mount chips they are sometimes glued to the board and tracks can be easily damaged, I allways cut the legs close to the body with a scalpel and remove them one at a time. Fitting a new divice is made easier by a tiny dab of glue to hold it in place it is amasing how "sticky" solder can be without the component held in place.

These tasks get easier with practice so its worth honing your skills on a junk piece of kit first.

Alan

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Cutting the legs/pin first then remove the body of chip but be careful there are no tracks passing under it (it is possible to grind it thinner then place new chip on top) remove legs with solder wick or a solder sucker. Re soldering is best done under a stereo microscope with a very small tip thin solder and a solder flux pen. Get hold of a scrap board and with some cheap e-bay chips have several practice goes after all experience will pay. I'm over Severn bridge should you wish help and equipment.  

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Thanks Stub

Part of the reason I'm hesitating on this is recent experience replacing popped electrolytics on a PC motherboard.
My soldering iron is powerful enough to do jobs like fitting a new 5.5x2.5 power plug, but after snipping the electrolytics off of their legs, it failed to melt the solder on any of the remaining legs.
So a hotter more concentrated approach was needed, with the risk of damaging the track and adjacent components.
Though your idea of the hot-air gun is appealing - do they really get that hot, 60/40 melts at 188C/370F?
Michael

The thing about motherboards is that they are multilayer PCBs and some of those internal layers are often include hefty ground planes and power buses - and the caps will be wired in to these. This means they will rapidly suck the heat out of a small iron, even if the visible pad is very small.

You should find SMD much easier to desolder.

This £9.99 hot air gun from Screwfix does 450 and 600 degrees C. http://www.screwfix.com/p/energer-2000w-heat-gun-240v/59740

it comes with a reducer nozzle (must get one myself).

Or there's something like this SMD rework station with soldering iron and small hot air gun

http://www.amazon.co.uk/852D-Soldering-Rework-Station-Nozzle/dp/B009POW2XA

Don't forget the whole board will have been at 230 degrees when the SMD components (including any SMD capacitors) were attached

Edited by Stub Mandrel

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Many thanks to all of you for your replies.

They have given me a number of choices and the confidence to consider DIY as one of them.

Michael

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Well one of the StarPatch gurus made some suggestions that have sorted the problem, the ports have sprung into life.

Thanks anyway to everyone who replied.

Michael

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The Max 232 family are pretty bombproof, although I did blow up one in my BBC B (it was the RS423 chip, even if it wasn't the maxim one...).

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Well one of the StarPatch gurus made some suggestions that have sorted the problem, the ports have sprung into life.

Thanks anyway to everyone who replied.

Michael

My Bad - I meant general Meade LX200 and MyStar guru, not StarPatch

Michael

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