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Help with an Intel Above Board/AT

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    Help with an Intel Above Board/AT

    Hi Everyone,

    I've been a computer enthusiast my entire life, however the last couple of years have seen me catch the retro PC bug rather badly. Luckily for me I kept much of my old hardware, and some of the things that I don't have I've managed to snag at thrift stores and the like. A couple of months ago I was at my parents place and dug out our first computer along with the monitor and printer and have spent the last little while restoring it to how I remembered it as a kid and playing with it again which has been a ton of fun. The forums here have been an invaluable resource over the years, however I can't seem to find anything that relates to my problem.

    Once I got it working I decided to add a bit more memory in the form of an Intel Above Board/AT that I managed to snag off Ebay to help smooth out Windows/286 performance. The board is fully populated with 1664 KB of RAM. Rows 0 and 1 have 64K DIPs while the rest are filled with 256K DIPs.

    The board is installed and mostly working except for an error when EMM.SYS loads stating that I have defective chips on the board and it initializes only to 1536KB. I've run the Intel confidence tool numerous times, including one session with 10 consecutive runs and all the memory chips come back fine. The tool includes an option to set the first two rows as 64K chips while the rest are 256K, as is installed on my board. In this configuration it passes. If I select all 256K chips the tool naturally says all the 64K chips are defective.

    This leads me to believe that the EMM.SYS driver (the one included with Windows/286 2.1) is having fits with the mixed memory sizes. I've tried an older version of the driver from an image of the original installation disk with the thought that it might deal with the mixed chip sizes better, but it results in a different error telling me that my machine is not completely AT compatible (Packard Bell 286 running at 12 MHz).

    It's not an earth shattering problem, but the error on startup is annoying and I would rather not move chips around on a board this old if I can avoid it.

    Have any of you encountered this problem before and have any kind of solution?

    Looking forward to contributing here moving forward!

    #2
    I don't remember for certain, but I don't think different DRAM chip sizes on the same Above Board was a supported configuration

    Comment


      #3
      Max is almost right. According to STASON.ORG, you should only have 64K chips in bank 0 for 1664KB. All others should be 256K.

      Comment


        #4
        Originally posted by ibmapc View Post
        Max is almost right. According to STASON.ORG, you should only have 64K chips in bank 0 for 1664KB. All others should be 256K.
        Yes, I noticed the same thing on STATSON.ORG when I was making sure the dip switches were set correctly. It explicitly states that SW2/1 should be switched to the ON position to support both sizes at once. In addition all of my 64K chips are in Bank 0 as directed. This is of course assuming that the website is accurate.

        The Above Board confidence tool (from 1986) has an option to check the board with 64K chips in bank 0 and 256K chips everywhere else and it passes. It's very confusing.

        The other problem is that documentation for the Above Board/AT has been impossible to find so far.

        Comment


          #5
          hello
          some information here:
          http://cd.textfiles.com/pier02/010a/
          INTMEMRY.ZIP Above Board Technical Specs for Adding/
          Dealing with Memory - all.
          ..but if it answers you question - i dont know
          /cimonvg

          Comment


            #6
            Originally posted by Cimonvg View Post
            hello
            some information here:
            http://cd.textfiles.com/pier02/010a/
            INTMEMRY.ZIP Above Board Technical Specs for Adding/
            Dealing with Memory - all.
            ..but if it answers you question - i dont know
            /cimonvg
            Sadly the zip file seems to be empty.

            Comment


              #7
              okay , same file another server..
              http://annex.retroarchive.org/cdrom/...R40/index.html

              /cimonvg

              Comment


                #8
                Thanks for the link!

                After reading through the relevent files it definitely confirms that having 64K chips in bank 0 with 256K chips everywhere else is a valid configuration. I also confirmed that my DIP switches are set correctly. Still no idea why the EMM.SYS driver is reporting the smaller chips as faulty.

                I'm going to hunt around and see if I can find another version of the driver other than the two that I have.

                Comment


                  #9
                  Originally posted by AndyM1981 View Post
                  Thanks for the link!

                  After reading through the relevent files it definitely confirms that having 64K chips in bank 0 with 256K chips everywhere else is a valid configuration. I also confirmed that my DIP switches are set correctly. Still no idea why the EMM.SYS driver is reporting the smaller chips as faulty.

                  I'm going to hunt around and see if I can find another version of the driver other than the two that I have.
                  Tried these versions offered here?
                  http://files.mpoli.fi/hardware/SETUP/INTEL/

                  Comment


                    #10
                    Originally posted by maxtherabbit View Post
                    Tried these versions offered here?
                    http://files.mpoli.fi/hardware/SETUP/INTEL/
                    Just gave those both a try and still the same.

                    I've also tried versions from 1987 and 1989 that give the same error. At least the one from 1989 does it without screaming out the PC speaker so I've switched to that one for now.

                    Did anther test on the chips for 15 rounds of the Intel confidence tool and they still checked out, so I'm stumped.

                    Perhaps the 64K chips are dedicated to providing conventional memory backfill and if they're not used it generates an error?

                    Comment


                      #11
                      Is your ISA bus also running at 12Mhz? If so, are all your chips 80ns or faster? If it is 6Mhz, are they all at least 150ns or faster? Does it has jumpers for RAS and CAS? Are they set correctly? Have you tried 3rd party programs like Checkit and such to see what they say?
                      Last edited by Moogle!; March 18, 2020, 08:26 AM.

                      Comment


                        #12
                        Originally posted by Moogle! View Post
                        Is your ISA bus also running at 12Mhz? If so, are all your chips 80ns or faster? If it is 6Mhz, are they all at least 150ns or faster? Does it has jumpers for RAS and CAS? Are they set correctly? Have you tried 3rd party programs like Checkit and such to see what they say?
                        I'll give Checkit a try and see what it says.

                        As far as I know the bus is running at the ISA standard 8 MHz. I actually thought it might be the case and downclocked via the Turbo button, but the memory test on the board then froze on POST. It was fine back at the faster 12 MHz clock.

                        All the chips on the board are rated for 150ns. Other than the error on startup the board is working fine and the remainder of the memory is accessible. I've loaded it hard in Windows/286 with multiple applications open at once to test it and it has been fine.

                        No jumpers for that on the board. Just the DIP switches to select memory split between conventional backfill, extended and expanded as well as the chip size and the IO address.

                        If I remember correctly the ISA bus includes a wait state specifically to stabilize things on higher clocked machines like 286s, I could be wrong however.

                        Comment


                          #13
                          Also, do you have any rom shadowing or memory remapping options turned on in the BIOS? Does the motherboard have jumpers that define the amount of ram, which was common on older 286s.

                          Comment


                            #14
                            There is a floppy image, that I think is for this card, at minuszerodegrees. I donít know if it will help. There is also a manual, but itís for a slightly different card.

                            http://www.minuszerodegrees.net/manuals.htm#Intel

                            Comment


                              #15
                              So I ran Checkit and it did not report any errors. That being said it only saw the 1536 KB of memory on the card that was initialized in the driver, so it didn't really test the 64K chips.

                              I have ROM and and Video shadowing turned off. That 384 KB have been turned into extended memory. I tried disabling that to see if it made a difference and there was none.

                              Sadly my motherboard has no jumpers to allow me to change the conventional memory allotment. It's stuck at 640 KB.

                              This has me stumped. I'm thinking in the end the only way to fix this is to either pull the chips and leave it at 1.5 MB, or remove the 64K ones and replace them with 256K.

                              Comment

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