Amiga Technical Resource

Replacing a memory SIMM socket


Introduction:
A common problem with the Amiga A4000D motherboard is that the plastic retaining clips on the sides of the memory SIMM (Single Inline Memory Module) sockets break off, so the memory no longer stays seated in the socket correctly, also causing intermittent or no electrical contact.
While various people try cable ties, tape and glue(!) to attempt fixing the SIMMs in place, the only real solution is to replace the entire socket.

This guide will cover removing the old sockets and fitting new replacements which have metal clips.
Original SIMM sockets on A4000D

Original plastic SIMM sockets in A4000D motherboard.

Disclaimer and caution

While the information on this page has been checked and is correct to the best of my knowledge, there is still the possibility of unintentional errors.
Please report any errors directly to this address so they can be corrected.

As with any repair work to delicate electronic equipment, you risk causing further damage to your system or yourself. I cannot be held responsible for any equipment damage or personal injury.

It is strongly advised that you possess some good common sense and preferably have previous experience in working with electronics before undertaking any repair on your system.
As always, you should take all anti-static precautions when working with semiconductor devices.



Things you'll need:
AmigaKit_logo.gif (2340 bytes)


Removing and replacing the sockets:
  1. The most difficult part of the job is of course removing the old sockets from the motherboard without causing any damage to the board. Because each socket has 72 pins which are soldered into "plated through holes", great care needs to be taken with the de-soldering process as it's all to easy to damage the through hole plating or tracks on the PCB.
    The most common way of de-soldering such a device is to use a vacuum solder sucker (hand operated or electric) and/or the use of de-soldering braid/wick. This is not only time consuming, but has a very high risk of causing PCB damage.

    In this example, I'll be using a surface mount device (SMD) hot air rework tool to assist with the de-soldering. Though there are no SMD components involved with this job, the hot air rework tool allows us to quickly de-solder the old sockets with less risk of damaging the PCB.


  2. Fit a medium (5-6mm inside diameter) single tube nozzle to the hot air rework tool. Set the heat and the air speed to medium.
    You can see below I've used a heat setting of 3 and an air speed of 2, though using a higher airflow and a slightly hotter temperature may assist with the job. Switch the tool on and leave it to heat up for about a minute.
    Rework tool settings



  3. Position the tip of the tool's nozzle about 5cm above the board and heat one half of the socket's solder joints. We want to concentrate on one end only to begin with as attempting to heat the whole socket at once will require too much heat which will damage the PCB.
     Important! Never hold the nozzle in one spot when it's close to the board!! Keep it moving all the time, otherwise the concentrated heat in one area can scorch the circuit board or cause it to blister.
    Heat half the socket

    Don't forget you can click on these images for a larger version.
  4. After approximately 1-2 minutes of heating, the solder will begin to melt. Using a pair of small pliers to grab the socket on the opposite side of the board, gently rock the socket from side to side. You'll feel when the solder melts; the socket will suddenly feel very loose. Heat for another few seconds and then use the pliers to lift the end of the socket out of the PCB. The socket's plastic body will fold very easily.

    If the socket will not lift out of the board, do not force it, as this indicates the solder has not yet fully melted.
    Lift the socket end from the PCB

    Apologies some images are a little blurry, making that damn camera focus was next to impossible!
  5. Once one end of the socket is partially removed, the easiest way to remove the rest is by applying heat to the top side of the socket. Using a distance of 5-10cm from the rework tool nozzle and the metal pins of the socket (from the side), gently heat for approx 10 seconds.
    Heat the top side of the socket



  6. As the solder on the pins gradually melts, use a small screwdriver or fine pliers to help lift the pins and socket body out of the board. Do not force the pins out of the board as this will cause PCB damage. The socket will lift very easily when the solder has melted.
    Remove pins as the solder melts



  7. Once the socket is removed, use de-soldering braid/wick or a vacuum removal tool to carefully clear the old solder from the PCB.
    Check very carefully for any PCB track damage. Once the new socket is fitted, it is very difficult to diagnose and repair a PCB problem.
    Clear old solder from PCB



  8. Repeat removal procedure for any other damaged sockets which require replacement.



  9. Locate the new socket and test fit it into the PCB. Due to the slight size differences, the old sockets may require trimming for the new socket to fit alongside.
    New SIMM socket

    Old socket needs trimmed



  10. From the image above, you'll see that the new socket doesn't quite fit. Simply use small side-cutters to trim the two protruding pieces of plastic from the neighbouring socket.
    Trimming protruding plastic pieces



  11. Fit the new socket into place and solder the joints on the bottom side of the PCB.
    If you are fitting more than one of the new sockets, the new sockets will not require trimming as their shape allows them to fit correctly in the PCB alongside each other.
    Clear old solder from PCB



  12. Before fully fitting the motherboard back into the case, populate the memory SIMMs, connect up power, monitor, hard drive, etc. Power on the machine and check the fast and chip memory is showing correctly.

    Remember that with A4000 memory, the motherboard only addresses a maximum of 2MB chip memory and 16MB fast memory on board.
    For 2MB chip memory (socket U261), you generally have to use a 2MB SIMM. Other sizes, such as 4 or 8MB will only show up as 1Mb.
    For 16MB fast memory, you should populate sockets U850 - U853 with single sided 4MB SIMMs.

    If the memory is not showing up correctly or at all, check the SIMMs in a working machine, or use different SIMMs. Check for soldering shorts on the bottom side of the board.

    More detail on the type of SIMMs you can use here.



Questions, comments, errors? Email me.






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