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Thread: IBM 5155 RAM upgrade questions

  1. #21
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    That looks rather promising, the only question is driver availability, but at least it's got the documentation with it.

  2. #22
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    Quote Originally Posted by vwestlife View Post
    Here's a likely possibility, for only $25 + free shipping:

    http://www.ebay.com/itm/272152675523
    This card may be difficult to fit in a 5155. There are only two full length slots available and the CGA card takes one of them. With the daughter card on it may interfere with things next to it.

  3. #23
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    It really depends on the thickness of the daughtercard, and how slots are arranged. You might also be able to squeeze it into slot 2, even if it does intrude into the next slot (which isn't full-length due to the front panel connectors).

  4. #24

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    Thought I'd update/close this thread - I recently bought an AST Six Pack Plus, populated with 256k, for a great price. Very excited, as finding software to run on this computer, that will fit in 256k of RAM has been admittedly frustrating.

    All I need is a hard drive now, and this computer will be right where I want it!

  5. #25

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    Hello,
    I have an ibm 5155 256k, I want to upgrade to 640k, the current chips are mk4564n from mostek in bank 0 and bank1, can I use 41256-15 for the upgrade? the timming are not the same, is that a problem? what exact reference would you recommend for the 41256?
    does the following reference work?
    Fujitsu MB81256-15
    Hitachi HM50257-15
    Mitsubishi M5M4256-15
    NEC uPD41256-15
    OKI MSM41256-15
    TI TMS4256-15
    Toshiba TMM41256-15

    Thank you for your help.

  6. #26
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    Quote Originally Posted by andromeda92 View Post
    Hello,
    Welcome to these forums.

    Quote Originally Posted by andromeda92 View Post
    I have an ibm 5155 256k, I want to upgrade to 640k ...
    Presumably, you have seen upgrade instructions, such as the one at pointed to in note 1 of [here].

    Quote Originally Posted by andromeda92 View Post
    ... the current chips are mk4564n from mostek in bank 0 and bank1, can I use 41256-15 for the upgrade? the timming are not the same, is that a problem?
    The -15 represents 150 ns. No problem.

    Quote Originally Posted by andromeda92 View Post
    what exact reference would you recommend for the 41256?
    does the following reference work?
    Fujitsu MB81256-15
    Hitachi HM50257-15
    Mitsubishi M5M4256-15
    NEC uPD41256-15
    OKI MSM41256-15
    TI TMS4256-15
    Toshiba TMM41256-15
    I would expect that any of the 150 ns (or faster) parts listed at [here] to work, but I cannot give any guarantee.

    If you do not wish to gamble, you could look for photos of the 256-640KB motherboard on the Internet, and see what those motherboards have fitted.

    On my fully functional 256-640KB motherboard, banks 0 and 1 contain a mixture of Oki MSM41256-15 and NEC uPD41256-15.

  7. #27

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    thank you for the information,

    but I saw two different documents concerning the upgrade to 640k,
    one in the link and another in this link
    which says Install a jumper wire from pin 1 to pin 8 on U44 (pal circuit in U44).

    Should we do it or not?

    it's weird, because the Oki MSM41256-15 and NEC uPD41256-15 have cycle 256cycle/4ms,

    I saw in a documentation but I do not know anymore or, that it was better to take 128cycle / 2ms, because it can not work, the memory chips of the card 5155 have 128cycle / 2ms.
    link

  8. #28
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    Quote Originally Posted by andromeda92 View Post
    Hello,
    I have an ibm 5155 256k, I want to upgrade to 640k, the current chips are mk4564n from mostek in bank 0 and bank1, can I use 41256-15 for the upgrade? the timming are not the same, is that a problem? what exact reference would you recommend for the 41256?
    does the following reference work?
    Fujitsu MB81256-15
    Hitachi HM50257-15
    Mitsubishi M5M4256-15
    NEC uPD41256-15
    OKI MSM41256-15
    TI TMS4256-15
    Toshiba TMM41256-15

    Thank you for your help.
    Quote Originally Posted by ibmapc View Post
    You should consider THIS MOD to put 1 MB on the motherboard. The thread linked HERE explains the process. It's a long thread but worth the reading in my opinion. I convinced Chuck(G) to help program the GAL to make it work some years ago. I would be glad to help you with the mod if you are interested. I can supply a programmed GAL and adapter for cost of postage. Just PM me.
    I'm 99.8% sure that either of the 41256 chips will work, But you'll need enough to fill all banks if you do 1 Meg Mod.

  9. #29
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    Quote Originally Posted by andromeda92 View Post
    but I saw two different documents concerning the upgrade to 640k,
    one in the link and another in this link
    which says Install a jumper wire from pin 1 to pin 8 on U44 (pal circuit in U44).
    Should we do it or not?
    The basic steps of the 640K mod are:
    * Put 41256 chips into RAM banks 0 and 1
    * Put a 74LS158 chip into socket U84
    * Ground pin 1 of chip U44

    The grounding of pin 1 of U44 can be done in different ways.
    Some examples:
    Example: Some instructions may have you ground pin 1 of U44 by jumpering pins 1 and 2 of jumper pad E2. E2 photo at [here].
    Example: Some instructions may have you ground pin 1 of U44 by placing a length of wire-wrap wire underneath the U44 chip, using it to join (by wrapping around the pin) pins 1 and 8 of U44.
    Example: Some instructions may have you ground pin 1 of U44 by soldering a wire between pins 1 and 8 of socket U44.

    Which method you choose to ground pin 1 of chip U44 is up to you.

    Quote Originally Posted by andromeda92 View Post
    it's weird, because the Oki MSM41256-15 and NEC uPD41256-15 have cycle 256cycle/4ms,
    I saw in a documentation but I do not know anymore or, that it was better to take 128cycle / 2ms, because it can not work, the memory chips of the card 5155 have 128cycle / 2ms.
    link
    I have seen nothing to indicate that 41256 chips on a '640K mod' 5155 motherboard, or on a 256-640KB 5160 motherboard, need to be of 128cycle/2ms.
    A motherboard that is performing 256cycle/4ms refresh, can use either 256cycle/4ms or 128cycle/2ms chips.

  10. #30
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    Tex Elec offers the Lo-tech 1Mb card for $57.99. No soldering required.

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