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Thread: TRS-80 Model 4P RAM question

  1. #1

    Default TRS-80 Model 4P RAM question

    So I'm finally getting around to working on my model 4P.

    According to what I've been reading, the issue that I have is that some of the RAM is bad.

    The chips are labelled: 8040665 FQD8446, but 2 are 8040665 TQD8446

    My question is: Are those really the same? If I picked up some TQD8446 chips, would those work in the FQD8446 slots?

  2. #2
    Join Date
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    The 4P wants 4164 200 ns or better. This thread may help you
    http://www.vcfed.org/forum/showthrea...Memory-Upgrade

  3. #3

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    Quote Originally Posted by rlauzon View Post

    The chips are labelled: 8040665 FQD8446, but 2 are 8040665 TQD8446

    My question is: Are those really the same? If I picked up some TQD8446 chips, would those work in the FQD8446 slots?
    You're unlikely to find any "TQD8446" chips. The "8446" refers to a single production week (week 46 of 1984). The difference between "TQD" and "FQD" is trivial.

    Any chips with the Tandy part number on them (8040665) are guaranteed to be compatible. But you don't have to try to find those. Lots of other 4164 chips should work. The main Model 4/4P requirement that not all chips will meet is that they must require only 128 refresh addresses (rather than 256). Here's a good list of lots of manufacturers' 4164 chips and their properties:

    http://www.minuszerodegrees.net/memory/4164.htm
    Last edited by Petrofsky; July 21st, 2019 at 04:33 PM.
    -Alan

  4. #4
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    Just bought a load from Bulgaria, all MN4164P, 150ns with the 128 bit refresh that seems to be the real problem

    They are on Ebay at 1.42 for two and while it states not tested, every one I got worked fine (i did buy 16 just to ensure I got enough to replace the bad chip and do the upgrade on my model 4 GA)

    serch for MN4164P-15-Page-Mode-DRAM-64KX1-150ns-NMOS-USED-2-pieces on Ebay

  5. #5
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    And as its a 4P, its just a jumper to move once the chips are in by the looks.

    http://www.classiccmp.org/dunfield/trs80/m4memory.pdf

  6. #6

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    Thanks!

    I was able to source some 4164 chips from Jameco. My 4P only has 64K right now, but it looks like I'll just upgrade it to 128K while I'm fixing the RAM.

  7. #7
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    Quote Originally Posted by rlauzon View Post
    Thanks!

    I was able to source some 4164 chips from Jameco. My 4P only has 64K right now, but it looks like I'll just upgrade it to 128K while I'm fixing the RAM.
    Are they the 128 cycle refresh chips or the 256 cycle refresh. If its the latter, they wont work but have similar part numbers.

    info here http://www.vcfed.org/forum/showthrea...th-128-refresh

    Looking at the Jameco website, https://www.jameco.com/z/4164-120-Sa...6_2290535.html type KN4166B have a 128 refresh cycle but https://www.jameco.com/z/4164-150-Ma...DIP_41662.html do not.

  8. #8

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    Quote Originally Posted by Gary C View Post
    Are they the 128 cycle refresh chips or the 256 cycle refresh. If its the latter, they wont work but have similar part numbers.

    info here http://www.vcfed.org/forum/showthrea...th-128-refresh

    Looking at the Jameco website, https://www.jameco.com/z/4164-120-Sa...6_2290535.html type KN4166B have a 128 refresh cycle but https://www.jameco.com/z/4164-150-Ma...DIP_41662.html do not.
    Thanks for the warning. I was going to get the wrong chips.

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