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Old 29 August 2019, 13:09   #1
Sim085
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Desoldering A1200 RF Modulator (How did you do it?)

Hello, I am trying to desolder the RF modulator from a broken A1200 motherboard. Here is what I tried and failed so far;

1. Put the soldering station to 450 degree, put the solder head on one of the soldered leg. Nothing happens. Solder on leg does not melt.

2. Put flux on the soldered leg and try again. Nothing happens. Solder on leg does not melt.

3. Put more solder on the soldered leg. This looks like it is going to work as when I touch the soldered leg again the soldering looks like it melts.

4. Use which to try and remove the access solder. This again looks like working. However there always remain some soldering and the RF modulator feels like still stuck.

I am not using any force. I try to gently lift the RF modulator while melting the solder on one of the legs but can't see any progress.

Anyone has any advice on how they removed this?

Should I be using the hot air station for this work? If yes what temperatures? It feels like soldering from factory is much hard to melt than soldering I apply fresh. Also want to point out that I am using the flat solder head (like the one attached) and I keep this clean through Steel Cleaning Wire Sponge.
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Old 29 August 2019, 13:19   #2
indigolemon
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I had no intention of keeping the RF modulator after I removed it, so i used snips to cut away most of it - then desoldering was much easier as I wasn't heating a massive lump of metal attached to a large groundplane anymore.
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Old 29 August 2019, 13:56   #3
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What soldering iron is it?

You will most likely need a more powerful soldering iron. The modulator being made out of metal and having a large surface area will quickly absorb the heat away from the soldering iron. Heating the iron up to 450C will only add a bit more headroom before it cools down to the point where it can't melt the solder anymore. Doesn't help the fact that it is also soldered to the ground plane which has a massive surface area draining the heat away from the iron.
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Old 29 August 2019, 14:29   #4
Sim085
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So what temperature do i need to use?



Quote:
Originally Posted by GearCross View Post
What soldering iron is it?
You will most likely need a more powerful soldering iron. The modulator being made out of metal and having a large surface area will quickly absorb the heat away from the soldering iron. Heating the iron up to 450C will only add a bit more headroom before it cools down to the point where it can't melt the solder anymore. Doesn't help the fact that it is also soldered to the ground plane which has a massive surface area draining the heat away from the iron.
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Old 29 August 2019, 14:32   #5
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It's not a question of temperature, it's all about the wattage of the iron. If your iron isn't powerful enough, the heat will be drawn from it before the solder has melted due to the large metal surface area of the modulator.
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Old 29 August 2019, 15:21   #6
Sim085
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I have a Fixpoint Digital soldering station. It has the following technical details;

power soldering iron: ca. 48 W
soldering iron voltage: 24V
frequency: 50 Hz
temperature range: 150-450 °C

Quote:
Originally Posted by Hewitson View Post
It's not a question of temperature, it's all about the wattage of the iron. If your iron isn't powerful enough, the heat will be drawn from it before the solder has melted due to the large metal surface area of the modulator.
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Old 29 August 2019, 15:24   #7
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The soldering iron needs to be powerful enough to keep itself hot after being in contact with the RF modulator's shield, or any large metal body. Both the RF shield and the massive ground plane on the motherboard will act like a heatsink, drawing the heat from the iron much faster than it can keep up, becoming unable to melt the solder. Adding more heat will only add a slightly larger margin, which can be useful if your iron is JUST barely powerful enough for the job you're undertaking, but in your case, it seems that your iron is heavily underpowered. For reference, 60/40 leaded solder (which is most likely what the Amiga is using) melts at about 180C.

For comparison, I went from a 15W iron to a 75W one for my tinkerings, and even on small soldering jobs, I noticed a massive difference. Stuff involving a ground plane was literally the difference between an unsuccessful desoldering job due to solder not melting enough, or not at all, and a clean, 5 second desoldering job.


EDIT: Just saw your reply. If that soldering station has real time temperature reading, check its temperature while you're trying to de-solder the RF modulator. Also, make sure the tip is securely in place.
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Old 29 August 2019, 15:47   #8
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If the tip is too small you won't be able to keep the heat in it either, even if the iron is powerful enough. You'll need a larger tip and a powerful iron to do it. My main iron is pretty small and works great for most things, but for doing the modulator I've used a gas-powered iron and a larger tip. What will also help is to preheat the modulator and surrounding area. Reducing the temperature difference between the modulator casing and the iron means less heat gets drawn away from the tip. If you have a hot air station, that can be used to heat the area for a few minutes beforehand.
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Old 29 August 2019, 16:43   #9
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The reason it was harder to melt the factory solder was partly because the surface was oxidized and partly because the contact area between the pad and a dry iron is very small (a small point). Applying flux (which is inside fresh solder) will remove the oxidization and coating the tip with a good amount of solder will increase the contact area, improving the heat transfer. The wattage of the iron is important, but not as much as the thermal capacity of the tip. Basically you need a tip with a large mass to minimize the temperature drop.

Even when you are able to melt the pads, that does not mean it will be easy to desolder. As you found out, there is always a little solder left which holds the pins in place. Even with a good desoldering station or desoldering braid (I like this) it is still not easy. Right after you remove as much solder as you can, it might be possible to push the pin to the center of the hole so it does not touch any of the sides when the solder hardens. If the pin is a tight fit, then that is not an option though.

I would say that you should probably just be a little destructive as otherwise mentioned. Will you ever want to reinstall the RF modulator? I know I never will.
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Old 29 August 2019, 16:49   #10
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Make sure you have solder on the iron tip too, to aid with heat transfer.
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Old 29 August 2019, 22:03   #11
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So trying again to remove the RF modulator...
I can see the temperature never goes down more than 5 degrees, i.e. from 450 it goes down to 445 and then up again, etc. However the things does not want to get stuck. The back small three pins have been ok, used wick to remove soldering no problem, but wick does not even have the strength to remove soldering from the three large pins.

So ... what was the other way how I can remove the RF modulator given I am going to throw it away? Can't understand how I can cut it off as there is no space between the RF modulator and the motherboard.

I have no intention to put the RF modulator on. All that is important for me is not to damage the motherboard in the process.

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Old 30 August 2019, 00:28   #12
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I took the top cover off, and ate away the PCB inside with the snips. Once that was gone I cut away at the outer frame. Just took my time and ate it all away bit by bit, taking care to avoid the components around it.
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Old 30 August 2019, 00:34   #13
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Quote:
Originally Posted by Sim085 View Post
Hello, I am trying to desolder the RF modulator from a broken A1200 motherboard. Here is what I tried and failed so far;

1. Put the soldering station to 450 degree, put the solder head on one of the soldered leg. Nothing happens. Solder on leg does not melt.

2. Put flux on the soldered leg and try again. Nothing happens. Solder on leg does not melt.

3. Put more solder on the soldered leg. This looks like it is going to work as when I touch the soldered leg again the soldering looks like it melts.

4. Use which to try and remove the access solder. This again looks like working. However there always remain some soldering and the RF modulator feels like still stuck.

I am not using any force. I try to gently lift the RF modulator while melting the solder on one of the legs but can't see any progress.

Anyone has any advice on how they removed this?

Should I be using the hot air station for this work? If yes what temperatures? It feels like soldering from factory is much hard to melt than soldering I apply fresh. Also want to point out that I am using the flat solder head (like the one attached) and I keep this clean through Steel Cleaning Wire Sponge.
I desoldered mine with a crappy 30W Soldering Iron couiple of years ago. Even did a small tutorial .. -ish...
http://www.exretro.com/galleries/com...%29/index.html

/eX
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Old 31 August 2019, 10:10   #14
Sim085
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Thanks to all for the great advice given here
I managed to remove the RF modulator. First I de-soldered all the internal stuff I could find within it and finished up with an empty box. I then added more and more solder to the pins holding the box to the motherboard, melted this while pulling gently. After doing this on all three legs the box was out. The three electrical pins at the back where a breeze to remove. Still think the solder for the pins must have something to it as the soldering wick still can't pull it out! Attached a photo of area after clean up.

Again many thanks to all.

I had read somewhere I can also remove some capacitor / capacitors after removing the RF modulator. Would anyone know which capacitors are these?
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Old 31 August 2019, 10:34   #15
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Quote:
Originally Posted by Sim085 View Post
Still think the solder for the pins must have something to it as the soldering wick still can't pull it out!
Desoldering braid needs a proper temperature before it will work - higher than what is needed to simply melt the solder, and your iron is simply not beefy enough to heat it up.
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Old 31 August 2019, 12:36   #16
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The other thing that sometimes helps in this situation is to bring in a 2nd soldering iron! Getting someone else to hold the 2nd iron is the best idea, so you can then remove the solder (you kind of need 3 hands - it can be done with two though).
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Old 31 August 2019, 21:37   #17
Sim085
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I do have a spare solder station (the first one I bought) so I might try this. Today received new soldering wick. At first I had some success managed to remove solder from one of the wholes. But the other two are no use so far. I do have one of those pens which should suck soldering somewhere around. So maybe will try that one as well.

Quote:
Originally Posted by GadgetUK View Post
The other thing that sometimes helps in this situation is to bring in a 2nd soldering iron! Getting someone else to hold the 2nd iron is the best idea, so you can then remove the solder (you kind of need 3 hands - it can be done with two though).
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Old 31 August 2019, 22:21   #18
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My way to do it:

1. Hot air handle mounted in retort stand, set to 160°C, heating the PCB from the bottom side (mainboard placed upside down), preheating for 5 minutes.
2. Apply gel flux to the joints.
3. Signal pins can be desoldered now, with regular soldering station, usually one by one.
4. For desoldering the shielding: transformer soldering gun, 120 watt, used together with desoldering pump.
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Old 31 August 2019, 22:23   #19
ChrisUnionNJ
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I used hot air on my station and blew the solder out on the heavy spots
with no problems..
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