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Thread: Upgrading the Amstrad Mega PC

  1. Default Upgrading the Amstrad Mega PC

    Hi All

    Ive got two Amstrad Mega PC's although im always on the lookout for spares and documentation etc.

    These came with a 386 SX 25 processor as standard and 1mb RAM

    One of mine has 8mb RAM (2 X 4MB simms) as well as the cyrix 486 drx2 50 upgrade. I know these are 30 pin simms and that the mega pc can only take 4mb max per free memory slot.

    Can you please tell me if I just bought 4mb 30 pin simms to fill the other two slots this would be ok. For example do I have to worry about parity, 60ns/70ns and all the ratings?

    I want to upgrade the computer but dont want to buy stuff I cant use.

    Some pictures are here of the simms currently installed - ive taken the pictures at an angle as I havent taken apart the computer fully yet.

    I am also wondering if someone can point me in the direction of where I can get the original cryix 3.5 floppies or files so that I can install them should I replace my hard drive

    Thank you in advance

    http://s1269.photobucket.com/albums/...d%20Mega%20PC/

  2. #2
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    A problem that you need to deal with is the 'barrel' batteries. At least one has started to leak (due to age no doubt) - the light blue one. How do I know? Photo #16 shows a green deposit on the solder joint of the battery, a classic sign.

  3. #3
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    I don't know about parity, but I bought a couple of 30 pin SIMMs at random, hoping them to be at least 1 MB each. When I installed them into my Amstrad MegaPC, they turned out to be 4 MB modules so now it got a whopping 16 MB RAM!

    It should be mentioned there is a bit of stuff to remove to reach the memory slots, but I'm sure you already have located it and figured it out. Basically I had to take away the front, and in order to remove the Megadrive card, I had to lift and pull it backwards in a way that I was unsure if I'd get everything back in place again. Basically you only want to upgrade the memory once.

    I have no idea about CPU upgrades though, if that is your unasked question if you can get an upgrade 486 into the machine.

    My biggest issue is that I should replace or at least remove the CMOS battery, since it is flat. I kind of remember getting into that but for some reason I didn't finish the task. Then I don't have any original parts, so I'm using a generic AT keyboard and regular monitors. Yes, plural since one monitor can handle the DOS/VGA resolution and one monitor can handle the Sega RGB mode. I'm on a hunt for a dual or multi scan monitor but those are hard to find. I even tried a RGB to VGA adapter board from China. While it happily converted the 15 kHz RGB to VGA, it was less successful at putting through the 31 kHz VGA signal without upscaling, despite the reseller spec suggests the board should be able to.
    Anders Carlsson

  4. #4
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    I think it is best that leaking batteries be dealt with as soon as possible, before damage starts to occur to the motherboard.
    An example of damage is shown in the following photo. Copper tracks have been 'eaten away'.
    http://www.minuszerodegrees.net/imag...tt_int_ext.jpg

  5. Default

    Quote Originally Posted by modem7 View Post
    I think it is best that leaking batteries be dealt with as soon as possible, before damage starts to occur to the motherboard.
    An example of damage is shown in the following photo. Copper tracks have been 'eaten away'.
    http://www.minuszerodegrees.net/imag...tt_int_ext.jpg
    Ive taken the battery out today. I have a replacement NICAD but also a cr2032 holder.but dont know if i need a rechargable 2032 or standard one. Would be grateful for any help. Im uploading some more pics to the album where I have taken it apart. Would be grateful for help on the memory front please.

  6. Default

    Quote Originally Posted by carlsson View Post
    I don't know about parity, but I bought a couple of 30 pin SIMMs at random, hoping them to be at least 1 MB each. When I installed them into my Amstrad MegaPC, they turned out to be 4 MB modules so now it got a whopping 16 MB RAM!

    It should be mentioned there is a bit of stuff to remove to reach the memory slots, but I'm sure you already have located it and figured it out. Basically I had to take away the front, and in order to remove the Megadrive card, I had to lift and pull it backwards in a way that I was unsure if I'd get everything back in place again. Basically you only want to upgrade the memory once.

    I have no idea about CPU upgrades though, if that is your unasked question if you can get an upgrade 486 into the machine.

    My biggest issue is that I should replace or at least remove the CMOS battery, since it is flat. I kind of remember getting into that but for some reason I didn't finish the task. Then I don't have any original parts, so I'm using a generic AT keyboard and regular monitors. Yes, plural since one monitor can handle the DOS/VGA resolution and one monitor can handle the Sega RGB mode. I'm on a hunt for a dual or multi scan monitor but those are hard to find. I even tried a RGB to VGA adapter board from China. While it happily converted the 15 kHz RGB to VGA, it was less successful at putting through the 31 kHz VGA signal without upscaling, despite the reseller spec suggests the board should be able to.
    Amiga monitors should work. Ive got the origina mega pc monitor but it has some issues I need to fix. Opening up the mega pc is a pain in the rear but I took lots of pics while I was doing it. Do you have pics of your 4mb simms?

    you can upgrade the mega pc to 486 using the clip on upgrades. see my pics

  7. #7
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    Quote Originally Posted by limboy777 View Post
    Ive taken the battery out today. I have a replacement NICAD but also a cr2032 holder.but dont know if i need a rechargable 2032 or standard one.
    I presume that you intend for the 2032 holder to be soldered in where the leaking Ni-CD was desoldered from. Whatever battery (unmodified) is placed there is going to be charged by the motherboard. Different battery technologies (Ni-CD, Li-ion, Ni-MH, ...) require different charging methods. The motherboard believes that a 3.6V Ni-CD is in place and will charge accordingly.

    Option: Ni-MH

    For this application, replacing a Ni-CD with Ni-MH should work (reference: 'Replacing NiCds with NiMH cells:' section of http://www.ka7oei.com/nicds.html).
    So you would need to locate a 3.6V Ni-MH battery.

    Option: Non-rechargeable

    A non-rechargeable battery should work if a blocking diode is placed in series with it. The blocking diode prevents the battery charging circuitry from charging the battery (because charging a non-rechargeable battery can result in damage).


  8. Default

    Quote Originally Posted by modem7 View Post
    I presume that you intend for the 2032 holder to be soldered in where the leaking Ni-CD was desoldered from. Whatever battery (unmodified) is placed there is going to be charged by the motherboard. Different battery technologies (Ni-CD, Li-ion, Ni-MH, ...) require different charging methods. The motherboard believes that a 3.6V Ni-CD is in place and will charge accordingly.

    Option: Ni-MH

    For this application, replacing a Ni-CD with Ni-MH should work (reference: 'Replacing NiCds with NiMH cells:' section of http://www.ka7oei.com/nicds.html).
    So you would need to locate a 3.6V Ni-MH battery.

    Option: Non-rechargeable

    A non-rechargeable battery should work if a blocking diode is placed in series with it. The blocking diode prevents the battery charging circuitry from charging the battery (because charging a non-rechargeable battery can result in damage).


    Thank you for replying.

    Option A -Can i replace a NICD with ANIMH with any other modifications i.e blocking diode

    Option B - What does a blocking diode look like? Do I need one if I put in a rechargable cr2032?

  9. #9
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    No, I didn't take any pictures during my memory upgrade. As for monitors, you would need a 1940, 1942, 1950 (?) or 1960 to do dual or multi sync. Obviously I'm not lucky enough to have either of those. My trusty old 1084's would only be good for 15 kHz modes.
    Anders Carlsson

  10. #10
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    Quote Originally Posted by limboy777 View Post
    Option A -Can i replace a NICD with ANIMH with any other modifications i.e blocking diode
    In this application, it is a straight replacement - remove 3.6V Ni-CD then replace with 3.6V Ni-MH.

    Quote Originally Posted by limboy777 View Post
    Option B - What does a blocking diode look like?
    The "blocking" is only describing what function the diode is being used for.
    One of the following cheap/common diodes will do: 1N4001 or 1N4002 or 1N4003 or 1N4004.

    Quote Originally Posted by limboy777 View Post
    Do I need one if I put in a rechargable cr2032?
    No.

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