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Old 11-25-2018, 11:47 AM   #1
roadrash
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Default Why do I struggle to desolder pentium 3 etc computer motherboards

I dont know if this is in the wrong section but it is a soldering issue.
I dont usualy have any problems soldering or desoldering things usualy and have just repaired a old crt monitor and soldering etc on this was easy. Today I have been trying to remove capacitors from a pentium 3 computer motherboard which is a mix of SMD & through hole. The problem I have is that I tin up my iron and hold it to the solder around the components leg but the solder just refuses to melt. These were only 68uf 6.3v electrolytics but i heated them for ages sometimes and they will not move. I can sometimes get a better result by holing some new solder against the leg and melt it onto the existing solder and then it will usualy help to get it melted although not always. Its like the solder on these type of motherboards is a different type and it doesnt conduct heat from the tip of the iron very well. there is no way I can desolder them with a suction tool because I cant get the solder to melt. Any solder I add to the existing solder still melts easily but the original solder underneath does't. Once I have the component out I can solder in the new one easily enough. I have a roll of RS cored lead solder I use which melts easily but Is this solder on these boards possibly lead free or some other solder and is there a special way of getting it to absorb the heat from the iron better.
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Old 11-25-2018, 01:30 PM   #2
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

this is typical when your soldering iron has insufficient wattage. for computer pcbs and computer graphic card pcbs, they are typically multi-layer pcbs with a lot of copper in them for the ground planes. this acts as a heatsink that sucks thermal energy. if your soldering iron has insufficent wattage, it will not be able to overcome this and the solder will not melt. a soldering iron with a wattage range of 60-80w is needed for computer pcbs.
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Old 11-25-2018, 01:38 PM   #3
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

If you have a hot air gun you heat the bottom of board with that but be careful doing this if there surface mount components on that side of the board they might fall off

Here is what I am talking about

ZD-939-L Digial Display

http://www.mpja.com/Hot-Air-Rework-S...info/34737+TL/

Or a ZD-939-A

https://www.newark.com/duratool/zd-9...vac/dp/81Y9840

Or you could use a Desoldiering Gun like this one

ZD-915

http://www.mpja.com/Desoldering-Stat...info/19034+TL/

I realize that you are in a another country but you can take the model number and find them near where you live
__________________
9 PC LCD Monitor
6 LCD Flat Screen TV
30 Desk Top Switching Power Supply
10 Desk Top Power Supply
10 Battery Charger Switching Power Supply for Power Tool
6 18v Lithium Battery Power Boards for Tool Battery Packs
1 XBox 360 Switching Power Supply and M Board
25 Servo Drives 220/460 3 Phase
6 De-soldering Station Switching Power Supply 1 Power Supply
1 Dell Mother Board
15 Computer Power Supply
1 HP Printer Supply & Control Board * lighting finished it *


These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board
2 Hem Saw Computer Stack Board

All of these had CAPs POOF
All of the mosfet that are taken out by bad caps

Last edited by sam_sam_sam; 11-25-2018 at 01:57 PM..
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Old 11-25-2018, 03:58 PM   #4
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

Replacing through hole caps on MB is quite troublesome specially if they are on power lanes. Adding cored lead solder before removing helps a lot.
But keep in mind you'll need a powerful iron, 80W or higher, because, as pointed out by @ChaosLegionnaire, inner power layers do have a huge area therefore acting as heat sink.
Also do not tin up your iron tip. Even better, use a large one (bezel alike).
Using a manual suction pump on the ground hole is quite often useless.
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Old 11-26-2018, 02:24 PM   #5
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

Thanls everyone for that info. I wondered why it was only these type of pcb gave me trouble. Is this I should use my gas soldering iron on then? Like that desoldering station sam_sam_sam.

Last edited by roadrash; 11-26-2018 at 02:28 PM..
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Old 11-26-2018, 08:25 PM   #6
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

no, gas irons are bad.
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Old 11-26-2018, 09:19 PM   #7
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

Quote:
Originally Posted by ChaosLegionnaire View Post
this is typical when your soldering iron has insufficient wattage. for computer pcbs and computer graphic card pcbs, they are typically multi-layer pcbs with a lot of copper in them for the ground planes. this acts as a heatsink that sucks thermal energy. if your soldering iron has insufficent wattage, it will not be able to overcome this and the solder will not melt. a soldering iron with a wattage range of 60-80w is needed for computer pcbs.
I have a few decades of soldering experience under my belt that has let me become proficient with motherboards at getting by with only soldering irons of 40 watts all though I use custom made tips. YMMV.
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Old 11-27-2018, 09:29 PM   #8
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

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Originally Posted by Sparkey55 View Post
with only soldering irons of 40 watts all though I use custom made tips. YMMV.
Just how did you modify your tip and only using a 40 watt iron
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Old 11-28-2018, 12:47 AM   #9
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

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Just how did you modify your tip and only using a 40 watt iron
I make my own tips from either brass stock or copper wire. I then file them to a chisel point with no more than about 1/16 inch thick at the tip. The real trick to using a 40 watt iron is not to use a long tip but keep it as short as possible and still be able to get it into tight places. Of course I still need to use additional help with preheating the board at times. That is when my hot air embossing blower comes in handy. I used to go to the trouble of clearing the through holes when I first started but now I just walk the new caps in the holes then add a little more solder at the bottom. This works for me.
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Old 11-28-2018, 06:21 AM   #10
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

The struggle is real. A couple of points that may have been mentioned but might need some clarification. The obstacle in your path to removing your components is thermal mass. The larger the mass, the more it acts as a heat sink. Increasing the heat is one way to deal with it. That can mean more wattage or increasing the efficiency of the heat transfer. Liquid flux or flux paste will aid with heat transfer. Lightly tinning the tip of your iron and wiping off the excess with a brass pad just before applying it to the area you intend de-solder will increase thermal conductivity. Using a damp sponge to clean the tip works well, but will reduce the temperature of your iron. The iron will then need to "recover" to maximum temperature. By then, the tip is already beginning to slightly oxidize, which will lower the thermal conductivity. Adding solder to the mass will help as well, the higher the lead content the better. 63/37 works well anywhere you need solder. As this new solder is introduced, the mass becomes a new alloy with a lower melting point. Pre-heating the board and/or adding a second controlled heat source will also help. You can also try reducing the amount of mass you need to heat. Carefully grinding away some of the solder mass with a rotary tool will reduce the overall mass you need to heat(this is very delicate as you don't want to damage the component if you intend to use it again or more importantly the board). That is not always an option, but simply creating a channel or groove around the leg of what you are de-soldering can reduce the ability for the mass to channel the heat away from the leg, thus allowing for a bit of flow. I(like the commentator above) have also made tips from solid copper wire that have worked well, keeping the new tip as short as possible and flattening the edge to a "chisel". Bare copper is an excellent thermal conductor and when a bit of flux is added and it has been tinned, it works far better than the tips that come with the soldering iron. If your gas iron has the ability to transfer more heat than your electric iron(and I assume it does), then there is no reason not to use it and you should be able to incorporate the copper tip method with it as well. I hope this helps. Take care.
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Old 11-28-2018, 07:30 AM   #11
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

just pre-heat the area with a hot-air station.
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Old 11-29-2018, 02:15 PM   #12
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

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Originally Posted by Sparkey55 View Post
I have a few decades of soldering experience under my belt that has let me become proficient with motherboards at getting by with only soldering irons of 40 watts all though I use custom made tips. YMMV.
Now you said that I remeber I had a old 240v 60w soldering iton that I made a tip for myself from a short bit of copper rod. Maybe I will try that. Can you tell me why I cant use a cordless gas soldering iron? I had to use it on that Viglen monitor I repaired recently so I could desolder a heatsink and then to resolder it back on. I could not get enough heat into it with a weller iron.

Last edited by roadrash; 11-29-2018 at 02:16 PM..
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Old 11-29-2018, 03:08 PM   #13
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

gas irons have no thermal control, they WILL lift tracks.

btw, get a set of these.
https://www.aliexpress.com/item/10-K...862870959.html
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Old 11-30-2018, 04:42 AM   #14
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

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gas irons have no thermal control, they WILL lift tracks.

btw, get a set of these.
https://www.aliexpress.com/item/10-K...862870959.html
See what you mean they are as hot as you want them and uncontrolled. Just have to be careful not to heat any longer than it takes to melt the solder. Those stainless needleslook very handy but use a pin myself to keep a hole open and stop it filling with remaining solder when iron is removed. Still they are better at getting more solder out because they look like they can file it out too.
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Old 11-30-2018, 05:07 AM   #15
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

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Originally Posted by roadrash View Post
See what you mean they are as hot as you want them and uncontrolled. Just have to be careful not to heat any longer than it takes to melt the solder. Those stainless needleslook very handy but use a pin myself to keep a hole open and stop it filling with remaining solder when iron is removed. Still they are better at getting more solder out because they look like they can file it out too.
When holes need to be cleared of solder I use either common nickel plated safety pins or unbent paper clips. The trick to keeping most of the solder from sticking to the pins is to scrape the pins often after a couple of holes with a dull box knife blade. YMMV
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Old 11-30-2018, 07:09 AM   #16
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

but for a € you get 10 of those in assorted sizes - why mess with needles & paperclips?
you can solder paperclips and needles btw, so dont use flux near them!!
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Old 12-02-2018, 01:16 PM   #17
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Default Re: Why do I struggle to desolder pentium 3 etc computer motherboards

Stainless steel dental pick set can be had for very cheap on Ebay and such. They are very useful in keeping tracks clear as well as manipulating component legs in hard to reach areas. I use them for both micro-soldering and point to point applications.
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