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Incompatability of AST Sixpackplus and NEC V20 Experienced with Clone XT

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    #16
    Thank you for checking with your card. I will continue forward with looking into ram and switches/jumpers. Seller of card told me it was removed from machine with 256K on the main board the same as my machine so I expected switches to be set correctly.

    I noticed that the sixth row of ram chips (counting from the end of the card inward) is different from the other five rows. The sixth row of chips are MCM6665BP20 all of the other chips are TMM4164AP-15. This is correct?

    Before getting your comments, today I checked the resistance of the three capacitors and the C45 is the only one that shows resistance. Tomorrow I will try to remove it from the card and see what happens. Will let you know what happens.

    Thanks again,

    Comment


      #17
      I don't think you can accurately check the resistance of a capacitor that is still in the circuit.
      PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

      Comment


        #18
        Originally posted by SailorEd View Post
        Before getting your comments, today I checked the resistance of the three capacitors and the C45 is the only one that shows resistance.
        Stone is correct. Making a measurement of C45 with it in-circuit, results in a measurement of the combined resistance of all devices on the -12V line, not just C45.

        Originally posted by SailorEd View Post
        I noticed that the sixth row of ram chips (counting from the end of the card inward) is different from the other five rows. The sixth row of chips are MCM6665BP20 all of the other chips are TMM4164AP-15. This is correct?
        Not a problem. My card uses a mixture of both MCM6665BP20 and TMS4164-15NL.

        Originally posted by SailorEd View Post
        Thank you for checking with your card. I will continue forward with looking into ram and switches/jumpers. Seller of card told me it was removed from machine with 256K on the main board the same as my machine so I expected switches to be set correctly.
        On my card, switch 7 on the switch bank is off. Looking at the documentation for the early versions of the card, switch 7 does not do anything, and there is nothing to indicate if switch 7 needs to be left off, or left on. You could try switch 7 off and see if it makes a difference, but I don't think it will.

        Comment


          #19
          Making Progress. Removed C45, checked with Ohm meter and short was gone. Installed in machine and it booted through the ram check and reported error as follows:
          512K OK
          08 RAM Bad 80004

          Does this indicate location of bad chip? How are the banks of ram and chips identified on the AST card?

          Thanks again for all the help getting to this point. I have some additional ram chips that I expect are OK; but not 100% sure.

          Comment


            #20
            It looks like the error is in the 5th bank. You can verify this by switching the 5th bank chips with the sixth bank chips. If the error moves accordingly you will know that there is a bad chip in the (now) 6th bank. Replacing those chips one by one with a known good chip will locate the bad one.
            PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

            Comment


              #21
              How are the banks numbered? From the BUS End (inside row out) or end of the card? Is the parity chip the bus plug edge or top edge of the card? Thanks Ed

              Comment


                #22
                Originally posted by SailorEd View Post
                512K OK
                08 RAM Bad 80004
                So, bit 3 in the bank starting at 512K.

                Originally posted by SailorEd View Post
                How are the banks numbered? From the BUS End (inside row out) or end of the card? Is the parity chip the bus plug edge or top edge of the card? Thanks Ed
                A quick experiment shows that it is the same as used in the first version of the card:
                Banks run from center of card to edge of card.
                Bits: From top to bottom are P/7/6/5/4/3/2/1/0

                Comment


                  #23
                  Originally posted by SailorEd View Post
                  Making Progress. Removed C45, checked with Ohm meter and short was gone.
                  I am sorry if any of the following is 'suck eggs'.

                  For a replacement capacitor, you have the option of using an aluminium electrolytic type. In fact, that is what AST used on my card. Photo at [here].
                  Height must not be such that the capacitor can make contact with an adjacent card.

                  Positive leg of capacitor into positive hole. For C45, the positive hole is the one closest to the DB25 connector.

                  In this application, a larger capacitance value is okay, e.g. 33uF

                  You can also use a higher voltage rating, e.g. 25V

                  Comment


                    #24
                    SUCCESS!! Rotated memory bank 4 & 5 and that got RAM OK up to 576. Then played swap and test until found two bad chips. Everything is now working except serial port given removal of C45. Really do not need it now and will leave it for a future activity as I will have to buy solder sucker, iron and capacitor(s).

                    Actually, the card does not have all chips populated, so I expect the serial chip(s) are what is missing.

                    Thank you so much again for all your guidance and coaching. I would not have been able to get it running without your and the forum support.

                    Buying from e-bay is a risk; sometimes you win and other times you are challenged to find value in what you buy.

                    We can now consider this thread closed and successful. Have a good weekend.
                    Best regards
                    Ed

                    Comment


                      #25
                      I placed tape over the B7 contact and installed installed card. Computer started OK!! Of course did not recognize card had been installed.

                      Comment

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