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Incompatability of AST Sixpackplus and NEC V20 Experienced with Clone XT

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    Incompatability of AST Sixpackplus and NEC V20 Experienced with Clone XT

    As noted in previous posts, I have also experienced the incompatibility of the SIxPackPlus board with the NEC V20 CPU chip.
    Booted OK until installed board. When installed, NOTHING; only a few rotations of fan in switching power supply. Remove board and boots OK.
    Wanted to install card to expand memory from main board of 256K up to 640K. I have now ordered Intel 8088 on e-bay to see if the SixPackPlus will boot on it.
    It is a clone system with two floppy, HDD and no math co-processor.

    #2
    Originally posted by SailorEd View Post
    When installed, NOTHING; only a few rotations of fan in switching power supply. Remove board and boots OK.
    Classic symptoms of a short circuit in the card (which overloads the power supply, stopping it from working).
    The short circuit is possibly in one of the tantalum capacitors.

    Comment


      #3
      Yeah, that screams of a rail shorting out on the card and less of a CPU failure.
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        #4
        Very easy to test for this with an ohmmeter.
        PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

        Comment


          #5
          Thanks for the suggestion. I have the ohn meter but not the knowledge to do the test. Would appreciate your advise on how to do it or where to go for the test procedure. Thanks Ed

          Comment


            #6
            Originally posted by SailorEd View Post
            Thanks for the suggestion. I have the ohn meter but not the knowledge to do the test. Would appreciate your advise on how to do it or where to go for the test procedure. Thanks Ed
            1. Remove card from computer.
            2. Turn card over so that the solder side of the card is showing.
            3. Put mutimeter into resistance mode.
            4. Refer to the diagram at [here].
            5. Measure the resistance of the +12V line by placing one of the meter probes onto the +12V pin, and the other probe onto either of the two ground lines. Note the resistance.
            6. Repeat step 5, except use the -12V pin. Note the resistance.
            7. Repeat step 5, except use the first +5V pin. Note the resistance.
            8. Repeat step 5, except use the second +5V pin. Note the resistance.
            9. Repeat step 5, except use the -5V pin. Note the resistance.

            If any of the resistance measurements are zero or a few ohms, then there is definitely a short citcuit (on the measured line).
            Perhaps report back your measurements.


            Note: Both +5V lines are measured, just in case a card maker decided to use only one (i.e. because of very low +5V consumption).

            Note: There is an assumption that the card maker has used both grounds on the solder side of the card, which is what I would expect. That can be proven by verifying that there is zero ohms between the two grounds.

            Comment


              #7
              I prefer to use a slightly simpler method. This involves testing for shorts where the PSU connects to the motherboard with the power off.

              First, remove all the cards from their slots. Then check the +5V, -5V, +12V and -12V connections for shorts to ground. If all is good there, insert the questionable card into a slot and repeat the test for shorts at the same four locations as just done. If there is now a short on one (or more) of the power rails it is due to the card you just inserted.
              PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

              Comment


                #8
                Thanks for the instructions. Will get it done tomorrow. I physically examined all the capacitors and they appear to be without physical distress.
                Ed

                Comment


                  #9
                  Thanks for the additional tip. Will try when have time to pull all cards from machine. Now it is running (knock on wood) with another card that I populated with chips.
                  Ed

                  Comment


                    #10
                    I have checked the resisance and got these results 20K scale Pin to Grd: 3-.29 5-open 7-0 9-0 29-.29
                    When using 20M scale appears that capacitors where being charged as readings on on 9 and seemed to start about 1.9 and go toward 0
                    Does this tells us anything about the condition of the board?
                    thanks
                    Ed

                    Comment


                      #11
                      Originally posted by SailorEd View Post
                      I have checked the resisance and got these results 20K scale Pin to Grd: 3-.29 5-open 7-0 9-0 29-.29
                      When using 20M scale appears that capacitors where being charged as readings on on 9 and seemed to start about 1.9 and go toward 0
                      Does this tells us anything about the condition of the board?
                      Well, the +5V and -5V appear to be okay.

                      The +12V and -12V show "0", suggesting a short circuit on both lines, however, it is highly unlikely that that is the case (both short).
                      I see that you are using a high scale. What do you read when you use the 20 ohm scale ?

                      Comment


                        #12
                        Checked using 200 ohm scale (no 20 scale on meter) with following results: 3-Open; 5-Open; 7-7.4; 9-Open; 29-Open.
                        Thanks for you input on what to do next?
                        Regards
                        Ed

                        Comment


                          #13
                          Originally posted by SailorEd View Post
                          Checked using 200 ohm scale (no 20 scale on meter) with following results: 3-Open; 5-Open; 7-7.4; 9-Open; 29-Open.
                          Thanks for you input on what to do next?
                          Partial short on the -12V line. Could be capacitor; could be something else. But forum history weighs heavily towards capacitor.

                          You can prove the 'short circuit on -12V line' hypothesis for yourself. Put a piece of sticky tape over the B7 contact, and then carefully (so as not to affect the tape) insert the card back into your computer. If the computer starts, it proves the hypothesis.

                          Provide us with a photo of your SixPakPlus card, or, point us to a photo of same on the Internet. If your SixPakPlus matches mine, I am in a better position to advise further.

                          Also, if you have not already, do a detailed visual inspection of the card, because the faulty component may be visually showing as damaged. With the capacitors, you are looking for signs like:
                          http://www.minuszerodegrees.net/imag...tantulum_1.jpg
                          http://www.minuszerodegrees.net/fail...upling_cap.jpg

                          Comment


                            #14
                            I physically examined both sides of card and see no physical deterioration of any components or leads touching.
                            I placed tape over the B7 contact and installed installed card. Computer started OK!! Of course did not recognize card had been installed.
                            I have attached pic of board.
                            Thanks again for all the help.
                            image1.jpgimage1(1).jpg

                            Comment


                              #15
                              Originally posted by SailorEd View Post
                              I have attached pic of board.
                              Your SixPakPlus card matches mine. Down near the edge connector are three blue tantalum capacitors, C44, C45, and C43. The middle one, C45, sits on the -12V line. Remove it (unsolder, or clip off) to see if it is the source of the partial short.

                              By the way, when you remove the sticky tape, it is a good idea to clean the contact in order to remove any 'sticky' residue.

                              Originally posted by SailorEd View Post
                              Computer started OK!! Of course did not recognize card had been installed.
                              I expect that the -12V is only being used to support the serial port. I covered up the B7 contact on my card, and as I expected, my card's RAM was still seen at power-on. That suggests that your card has additional issues. Switch/jumper configuration? Bad RAM in bank 0.

                              Comment

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