Socketing DRAM chip on 130XE

[ijor]

One of the RAM chips on my 130XE stopped working correctly. Soldering is not one of my few talents, so I asked a friend to replace the chip. I thought it would be better to solder a socket instead of soldering the new RAM chip directly. He is not very familiar with old through hole systems, but said it will be ok. While desoldering the old chip he noted that it was soldered on both sides of the board. He said he won't be able to do that with the socket, and it might be then better to solder the new chip directly instead of installing a socket.

 

Does this make any sense? Is is really important to solder the socket on the top side of the board as well? I searched and I found some special sockets that have pins like a chip, and I guess those sockets could be soldered on both sides of the board. But is this really needed, or important at all?

 

Thanks

[+DrVenkman]

The through-holes on vintage Atari computers are plated - there is a little hollow rivet of copper pressed into the hole to attach to a circuit trace on either the top or bottom of the board.  The old chip can be de-soldered like any component: using solder wick, a solder sucker or a vacuum desoldering pump to heat and remove solder surrounding each leg. Provided it's done correctly, the chip can be removed from the PCB once all the legs of the chip are clear of solder. Alternately, if the chip is well and truly dead, you can clip each leg off at the "shoulder" where it meets the plastic or ceramic body of the chip. The legs can then be removed from each hole by melting the solder with a soldering iron. Once all the legs are removed from the board, remaining solder may be removed from the holes via solder wick, a solder sucker or a desoldering pump.

[+bob1200xl]

The holes are plated thru from one side of the board to the other, so soldering either side connects both.

 

Bob

 

[ijor]

19 minutes ago, bob1200xl said:

The holes are plated thru from one side of the board to the other, so soldering either side connects both.

 

That's what I thought. Many thanks.

 

20 minutes ago, DrVenkman said:

Alternately, if the chip is well and truly dead, you can clip each leg off at the "shoulder" where it meets the plastic or ceramic body of the chip. The legs can then be removed from each hole by melting the solder with a soldering iron. Once all the legs are removed from the board, remaining solder may be removed from the holes via solder wick, a solder sucker or a desoldering pump.

 

Good recommendation. Thanks.

[manterola]

It makes no sense that soldering the chip directly is different than soldering the dip socket

[+Stephen]

1 hour ago, ijor said:

One of the RAM chips on my 130XE stopped working correctly. Soldering is not one of my few talents, so I asked a friend to replace the chip. I thought it would be better to solder a socket instead of soldering the new RAM chip directly. He is not very familiar with old through hole systems, but said it will be ok. While desoldering the old chip he noted that it was soldered on both sides of the board. He said he won't be able to do that with the socket, and it might be then better to solder the new chip directly instead of installing a socket.

 

Does this make any sense? Is is really important to solder the socket on the top side of the board as well? I searched and I found some special sockets that have pins like a chip, and I guess those sockets could be soldered on both sides of the board. But is this really needed, or important at all?

 

Thanks

Makes zero sense.  If soldering the chip directly to the board would get both sides, then the socket will too.  If done properly, a little bit of flux on top and bottom of the board will take care of everything.  The flux will basically "pull" the solder through the plated PCB and up onto the top of the PCB.  Solder only need to be applied from the bottom.  Adequate flux and heat will do the rest.

[ijor]

Ok, thanks everybody for making this clear.

 

Btw, just for my info, what about those sockets that have legs more similar to a chip. Such as this: https://www.newark.com/amp-te-connectivity/516-ag10d/dip-socket-16-position-through/dp/14F2702

 

Are they any better than "regular" sockets or are for special purposes? They seem to be more expensive.

[TGB1718]

5 hours ago, ijor said:

They seem to be more expensive.

That's extortion, over $6 for one, have a look on Amazon there's many different types, although some people

on this forum don't like the cheaper "side wipe" type of contact, but personally in over 40 years of using them

I've never had an issue with one.

[foft]

For desoldering I find I have to use a solder sucker, about 10 times on each pin, then braid on both sides. With lots of flux too from a flux pen. Then I still remove some tracks sometimes. Is there a better way?

[TGB1718]

36 minutes ago, foft said:

Is there a better way?

Unfortunately you just have to be careful, selecting just the right temperature in your iron so it's not too hot,

don't keep the iron on the pad too long, if it's looking like a difficult one, don't be tempted to keep the iron on

the pad and keep trying to unsolder it, I find if you let it cool, re-flow the joint with fresh solder and try again.

 

As said before, cut the legs off if you can, if not then as I say, just be careful.

 

I've removed many chips and whether it's luck or pure skill  I've not removed many pads/tracks.

 

Not a fan of braid, I think it tends to need too much heat to be effective, I use a 40+ year old Solderpult

and a Maplin temp controlled iron with a fine tip. 

 

I 

[+DrVenkman]

1 hour ago, foft said:

For desoldering I find I have to use a solder sucker, about 10 times on each pin, then braid on both sides. With lots of flux too from a flux pen. Then I still remove some tracks sometimes. Is there a better way?

Adding fresh solder to each pin first is incredibly helpful regardless of what tool you use to clean the through-hole. If you use a solder sucker, it shouldn’t require more than two or maybe three attempts on each pin to get most of the solder out. I use an Engineer solder sucker for small things like a capacitor or a resistor leg. I like it because it has a high-temp flexible silicone tip, which allows you to get a decent suction around the soldering iron such that you’re heating and removing solder at the same time. 

 

For IC’s and sockets, I use a Hakko FR-301 vacuum desoldering pump. Add a bit of fresh solder, apply heat to the pad and component leg for just a sec, wiggling it a bit as you do, then activate the pump. Clears the hole almost instantly. 

 

No matter what tools you use, once the holes appear clear, use the hot tip of your iron to wiggle each leg of the chip to ensure it isn’t stuck to the side of the via with a small invisible drop of solder and can move freely. Once the legs are all free, the chip should lift right out without a problem.

 

 

[TGB1718]

@DrVenkman that's a really nice chip removal, I can see why your a Doctor

 

[mimo]

I treated myself to one of these earlier this year. Not used it as much as I hoped but it has been brilliant for removing chips from two faulty XEGS machines I had (both needed new RAM and CPU)

 

https://www.amazon.co.uk/DESOLDERING-STATION-PLUG-D00672-DURATOOL/dp/B011873JQU/ref=pd_lpo_60_t_0/262-8237544-2140045?_encoding=UTF8&pd_rd_i=B011873JQU&pd_rd_r=34608e36-6bcf-4861-a8c7-a66ae8db3669&pd_rd_w=wVuJI&pd_rd_wg=LR4R7&pf_rd_p=7b8e3b03-1439-4489-abd4-4a138cf4eca6&pf_rd_r=A9B3KM2DC1AYBZP4HMJP&psc=1&refRID=A9B3KM2DC1AYBZP4HMJP

 

I bought it from CPC and at the time it was under £100

Edited December 8, 2020 by mimo

[ZuluGula]

I know that adding fresh solder helps with chip removal, but did anyone experimented with low temp solder used in SMD rework, like Fast Chip or Chip Quik? Will it work in Atari? It supposed to lower the temperature required to melt the solder and protect delicate XE pcb.

[Sugarland]

4 hours ago, ZuluGula said:

I know that adding fresh solder helps with chip removal, but did anyone experimented with low temp solder used in SMD rework, like Fast Chip or Chip Quik? Will it work in Atari? It supposed to lower the temperature required to melt the solder and protect delicate XE pcb.

 

As long as it conducts electricity and will hold things in place. Best to read up on these particular solutions and see what they say.  For chip removal I'm not so sure.

 

[ZuluGula]

It should work. I'm just asking if anyone here used it on Atari pcb and if it help anything. This stuff is not cheap.

 

 

[manterola]

When you don't care about the chip being removed, it is much easier to remove (even I can do it in a reasonable amount of time), like Dr. Venkman mentioned: you just cut all feet and then remove the feet one by one: apply heat to one foot, and then pull out that foot/pin. After the process is completed you might need to clean the passthru hole with wick or desoldering pump (sucker).

 

 

Edited December 8, 2020 by manterola