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IBM Eduquest 40 CPU Upgrade woes!

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    IBM Eduquest 40 CPU Upgrade woes!

    Howdy all,

    I recently acquired an IBM Eduquest 35, which besides a dying hard drive, works great and an Eduquest 40 planer\motherboard. To test the 40's board, I simply took out the 30's and put in the 40's in it's place. It also worked, which I was really happy to find out. I've read that you can add a 486\5x86 "Overdrive" chip into this slot and that it disables the soldered on 486 SX25, so you can use this to upgrade the processor. However, I've tried an AMD 5x86-133, an Intel 486 DX100, and a Cx486DX2-66 with no success. I insert the processor, turn the computer on, fans spin up and monitor powers up, and nothing. No image, no signs of life. Take the processor out of the upgrade socket, turn it on, and it springs to life.

    My question is this, has anyone successfully used this socket to upgrade their CPU, and if so what was the processor you used?

    Thank you!
    Travis

    #2
    Have you followed the advice here with regard to the use of 3 volt processors in the Model 40 processor upgrade socket:
    http://www.walshcomptech.com/ps2/25-upgrade.htm#eq40upg

    Any of Intel's 80486 "OverDrive" processors will work in this socket. The article above suggests that a "standard" 80486-type processor will also work, as long as it is designed for a 5 volt processor socket.
    Last edited by hmb; August 24, 2020, 07:23 AM.

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      #3
      Originally posted by travphel View Post
      Howdy all,
      I've read that you can add a 486\5x86 "Overdrive" chip into this slot and that it disables the soldered on 486 SX25, so you can use this to upgrade the processor. However, I've tried an AMD 5x86-133, an Intel 486 DX100, and a Cx486DX2-66 with no success.
      Apart from the 3.3V issue, you can normally not insert a standard CPU there. In order for the on-board 486SX getting disabled, you need to insert a 487 (which is actually a 486DX with an extra pin). An Overdrive will work as well, but again, not a standard one. You need an Overdrive made for the 487 socket.

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        #4
        Originally posted by Timo W. View Post
        Apart from the 3.3V issue, you can normally not insert a standard CPU there. In order for the on-board 486SX getting disabled, you need to insert a 487 (which is actually a 486DX with an extra pin). An Overdrive will work as well, but again, not a standard one. You need an Overdrive made for the 487 socket.
        Thank you so much! I'm guessing that would be the issue then as I've been trying just standard 486 chips I have around the house. I'll look for an overdrive made for the 487 socket. Any suggestions on a good one for this machine?

        Comment


          #5
          Originally posted by travphel View Post
          Thank you so much! I'm guessing that would be the issue then as I've been trying just standard 486 chips I have around the house.
          Make sure they're 5v chips and not 3, 3.3 or 3.45 volts, also make sure you have the CPU installed in the right orientation and centered in the socket. I remember seeing people back in the day installing 486 CPUs in the 487 overdrive socket offset one row of pins on motherboards with crappy LIF sockets that had loose enough tolerances to allow it.

          Another "gotcha" is that some 486 chipsets, especially Intel chipsets, refuse to work with any 486 that isn't Intel. I've had several such systems over the years which only work with Intel 486 CPUs, including my current Zeos 486. It won't boot with anything other than an Intel chip installed.

          Originally posted by travphel View Post
          I'll look for an overdrive made for the 487 socket. Any suggestions on a good one for this machine?
          The most compatible would probably be the DX/2 50 or 66. The only problem with such chips is they're hideously expensive. I remember a time when you couldn't give those things away, but now people want stupid money for them.

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