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68B09EP to 63C09EP Upgrade with socket

This procedure may differ in the images that are shown based on what model of Colour Computer you own. The methods involved are the same though. 

This procedure requires soldering. If you are uncomfortable with soldering, stop now. Go away and practice on scraps of vero board or old PCB's until you are.

As with most things there is more than one way to skin a cat. This method uses a destructive means to remove the CPU from the main board. It is quick and reliable. If there is a desire to retain  a working 68B09EP CPU then use a de-solder gun or struggle through with soder wick.  Those methods are not detailed here though.

This page shows the replacement of the 68B09EP with a 63C09EP with socket. The procedure assumes that the main board has already been removed and that if a PAL board is fitted it too has been removed.

 The procedure follows these steps:
  1. Remove the existing 68B09EP from the main board
  2. De-solder the CPU pins
  3. Remove remaining solder form PCB
  4. Solder socket into the main board
  5. Insert 63C09EP CPU into socket
Tools required:
  • Variable temperature soldering iron
  • Needle nose pliers
  • Solder sucker (if you don't own one Ebay it - cheap as chips)
  • Solder 0.8mm
  • Flush cutters or precision side cutters
  • Isopropyl Alcohol (IPA) 99.997% with brush
  • Flux (suitable for electronics) with brush
  • Anti static wrist strap - correctly grounded. 'Ideally' also an anti static mat for the bench that is also grounded correctly.
  • Multimeter (optional)
While it is not strictly necessary to use a variable temperature soldering iron there will be less pain if you do which will become obvious further down.

Precautions/Safety:
  • Be careful. These machines are getting old, think twice before you do something.
  • As with any work involving handling of static sensitive components it is imperative that an anti static strap be worn. The main danger with the Coco is zapping chips that are hard to replace, like the GIME. The problem with static is you might not know you have even caused any damage straight away until weird issues seem to pop up for no known reason. So make sure the strap is on and terminated correctly via a 1M Ohm resistor to ground before handling the board. Note: the resistor will already be in the wrist strap if the wrist strap is any good. To check measure the resistance from the wrist metal tab inside the strap to the end of the cable with a multimeter. Having said all that people don't always heed this so make your call and live with the consequences.
  • Be careful with tools near the board and slips of the soldering iron across PCB tracks. Position yourself so there is no strain in how you handle the tools and keep things in comfortable reach.
  • Wear eye protection when using IPA, flux and soldering.
  • Be aware of protrusions on the main board. One particular area to watch out for on the Coco 3 is the RGB header. If the board is laid flat on a surface either place something under the board to keep the header from being damaged or make sure only light pressure is applied to the top side of the board when working on it. Most of the work in this procedure is done with the board in a vertical position so both sides can be worked on at the same time.
  • Ensure there is proper ventilation in the room or the use of an appropriate fume extraction device is used to clear any chemical or solder fumes away

1. Remove the existing 68B09EP from the main board

In order to remove the existing CPU from the main board each leg of the CPU has to be cut. With a pair of small flush/side cutters go along each side of the CPU and cut each leg leaving enough of the leg still soldered to the board so a pair of small pliers can be used to grip the soldered end of the leg later on. Once all the CPU legs have been cut the CPU can be lifted free.

There should be two rows of pins left in the board. These will need to be de-soldered.




2. De-solder the CPU pins

All of the de-soldering in this procedure is done with the board in a vertical position.  For me this was the most straight forward way of doing it. It is possible to de-solder the CPU legs from the top side of the board if that is your preference.

Hold the board vertically using a small bench vice with protective rubber grips. It is essential that wherever the vice is placed that it is placed in a position that does not damage components and is tightened only enough to hold the board in place.

With some IPA and a small brush clean both sides of the board where the legs are positioned to clear away any substances which may inhibit a successful procedure. Wait for the IPA to evaporate and then apply some flux to the soldered legs on the bottom side of the board. I use liquid flux which can just be brushed on. Flux will make life easier and helps immensely with solder flow.

Set the soldering iron to 360 degrees Celsius and ensure the tip is clean and dab a small bit of solder on it to wet it.

WARNING: At no stage following should the leg tried to be pulled clear of the main board until the solder has melted completely in the PCB hole. Trying to pull the leg out when it isn't completely free to move can lead to damage of the PCB traces.

Now grip the first leg protruding from the top side of the board with the needle nose pliers and with your other hand apply the soldering iron tip to the other end of the leg on the bottom side of the board. Wait for the solder to melt and then gently pull the leg out with the needle nose pliers. Once you have the leg in the grip of the pliers you can just tilt your head to the bottom side of the board in order to locate the appropriate pin. Do this with the remainder of the legs.
   

By this stage all the CPU legs should be out. There will be solder still in the holes left behind by the leg removal. The next step is to make sure as much solder as possible is removed from the holes so the socket can be positioned with little to no resistance.



3. Remove remaining solder form PCB

Using the above step to remove the CPU legs will leave some solder in the PCB holes which will obstruct the socket from being inserted into the main board. The task now is to remove all the unwanted solder. This time we are going to heat the solder from the top side of the board and using a solder sucker extract from the bottom side.

Once again prepare the board by brushing some IPA over the PCB holes, evaporate then apply flux. Wet the soldering iron with a dab of solder and leave it set to 360 degrees Celsius.

Note: Sometimes the solder sucker doesn't work very well if there isn't enough solder mass to suck out of the hole. In these cases applying a bit more solder to the hole can help as contradictory as that may seem.

You will find that any holes which have lands/traces with a lot of copper will suck up the heat of the soldering iron. For those specific holes increase the temperature of the iron to 390 degrees Celsius. This should give enough heat to do the job. If not you may need to up it a bit more.

Load the solder sucker (push the piston down) and place it flush on the hole you are going to apply the solder iron to. Holding it in place apply the soldering iron to the PCB hole. Wait for the solder to melt and then press the button on the solder sucker. The solder should have been sucked out of the hole. Move the solder sucker away and press down on the piston again to clear it. Some solder may fall out but sometimes it can stay in the sucker until the next cycle.

The same process should be done with each hole. You can use a small tooth pick or component off cut to push through the last hole done as you go so you can keep track of what hole you're up to from both sides of the board. Keep the soldering iron tip clean and free of any unnecessary loading of solder. Apply flux to the board as required to ease the job.
   

Once all the holes have been cleared get a magnifying glass and make sure there is no damage to any of the pads. Try inserting the socket into the main board to test for fit. If the holes are clean it will fit but there may be a minimum of resistance depending on the type of socket pins that are on the socket. I typically go for the round tip pins. Do not force it. If you find that there is an obstruction in one of the holes go back and resolve it - typically by filling the hole with solder again and re-suckering it.

If the socket fits remove it and give the CPU area of the board a good cleaning with IPA and a brush.

All holes cleaned and ready for socket insertion.



4. Solder socket into the main board

Before inserting the socket take some time to identify the correct orientation the socket should go into the board. If your socket has a notch in one end of it then it should be oriented to match the notch that appears on the silk screen on the main board. This indicates the end of the CPU where pin 1 resides. While the socket can be inserted which ever way, it is more professional to line up the silk screen and the socket so no mistakes are made when the CPU is inserted. In addition if the CPU is ever removed and a replacement fitted there will be little chance of mistakes.

Place the socket on to the main board and make sure it won't fall out as the board needs to be turned over in order to solder all the pins. Use tape or when the board has been turned over make sure some padding is placed under the socket to make sure the pins protrude all the way out of the bottom of the board. 

With the board inverted so the bottom side is face up apply flux to both rows of pins. Solder one of the socket legs to hold the socket in place. Lift the board up and check that the socket is flush against the board before proceeding - if not  re-apply heat to the pin that was soldered and re-position until it is (see note below). This will hold the socket so the other pins can be soldered.  When the socket has been positioned start soldering the pins one at a time down one row then the other - start with the pin diagonally at the far end of the pin that was initially soldered.

Note: It is always better to get this right first time - heating the solder joint up multiple times is not a great idea and can lead to unreliable and bad solder joints. I'd even go as far as de-soldering and cleaning  that joint after the other pins are done and re-soldering it.

Give the newly soldered pins a good clean with IPA and brush. The socket is in place and now ready for the new CPU.
 
 

Optional - continuity test
Before proceeding I like to meter out all the socket pins to where they go on the board. Essentially what I'm trying to do here is make sure that all the solder joints are doing their job and making good connectivity to their associated traces.

5. Insert 63C09EP CPU into socket

At this point the CPU can be inserted into the board. My preference is to do this while the board is not mounted in the case, this will reduce flexing of the mother board. While there is not a huge risk of this in the way the board sit's in the case, why abandon good practise when there's no need to.

Before doing this inspect the CPU you are going to place in the socket. If it's new you will find that it likely won't insert into the socket without a great deal of man handling due to the tendency of chips to come with the legs slightly splayed outwards - like this:

     

Clearly this isn't going to fit. Obviously we need to bend the pins inwards so they align with the socket holes. Here's two ways you could do it and both ways will work. Note: there are actual tools which can do this job but for one off's it's not necessary.

Having used precautions to reduce static discharge (anti static strap) carefully hold the CPU between both hands and with one side laid flat against a hard surface (the anti static mat I used will work but something a bit harder would be better) GENTLY lever the CPU forward to cause the pins to bend inwards.

Be very measured when doing this and alternate SLIGHT adjustments with both sides of the CPU - that is, turn the CPU over and do the same thing with the other side and continue until the pins will line up with the socket. Try not to bend the pins backwards and forwards as they won't handle too much punishment.

So in this image the top of the CPU would be tipped away from you putting force on the bottom row of pins to cause them to bend inwards:


An other way of doing it is to use a flat object like a ruler which will clamp the pins flat and may other a bit more control. Once again this is better on a hard surface. If using this way place a fair bit of pressure on the ruler so the pins are held firmly. The mechanics are the same apply pressure to the top of the CPU and cause the pins to bend inwards. Note: the ruler should probably be a bit closer to the base of the CPU then what I show in this image.

 Like anything you could probably skin this cat using different methods but these work for me. Controlled force is the key to these methods - position your hands so they can administer slight pressure without having the full weight of your arm behind it which implies the pushing hand/s should rest against the bench or desk surface.

Now that the CPU can fit the socket it's time to insert the CPU into the socket. Most chips will identify pin one the chip with a small indent or notch or a mark. The CPU must be placed into the socket so that pin one mates with pin one on the mother board. This is why it was important that the CPU socket be soldered into the mother board so it also matches with the PCB pin out. Use the image below which shows the CPU mounted in the socket. Zoom in and you will see the correct orientation of the CPU. Note: this is for a PAL Coco3 but an NTSC version will have the same identifying marks on the PCB etc.

As extra support it's good to place the mother board on something that can support directly below the CPU socket so when you push the CPU into the socket the pressure is applied to just that point. In my case I used two pieces of anti static foam - could be anything that will do the job but better if it is a bit softer so as not to damage any of the solder joints on the bottom of the board. In addition the padding will keep the RGB pins from getting squashed (Coco3).

 
 

It is essential the pins line up otherwise damage will occur to the pins. Carefully line the CPU pins up with the socket and apply a downward force so the CPU just engages the socket and you can see all the pins have penetrated the socket. After you have triple checked this push the CPU the rest of the way into the socket. You may find the CPU goes all the way in on the first push. This will vary depending on what sort of socket was used. 

If all went well the CPU should be sitting proudly in the socket and you are ready to re-assemble and test. Before applying power double check the CPU orientation is correct otherwise bad things will happen. Good work!