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DIAGNOSING MEMORY PROBLEMS IN PC

Discussion in 'PC Tricks, Tutorials, Softwares And Solutions' started by Babadinho, Oct 15, 2010.

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    Babadinho Administrator

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          If you encounter the message "parity error" while operating your PC, a
          malfunction has occurred somewhere in the PC's memory (RAM).  In many
          instances, a parity error can be traced to a defective RAM chip or one
          that is seated poorly in its socket.
         
          To find the cause of the parity error, turn off the PC, wait about five
          seconds, and turn it on again.  After flipping the power switch on, the
          PC automatically runs a series of diagnostics which tests different
          parts of the system.  If a memory problem exists, a PARITY CHECK 1 or
          PARITY CHECK 2 error message will appear.  This article will help you
          interpret these error messages, isolate defective memory chips, and
          correct the situation.
         

          System Board Memory
         
          Early PCs have system boards which hold only 64K of RAM.  These system
          boards have four parallel rows (or banks) of nine 16K 4116 RAM chips.
          Newer PCs and XTs with 256K system boards have four parallel rows of
          nine 64K 4164 RAM chips.  In both cases, each row has eight chips for
          memory (data bits) and one for parity checking (parity bit).
         
          When facing the PC chassis from the front, the row of chips closest to
          the front is designated row 3, with the next row being row 2, then row
          1, and row 0 next to the expansion slots.  In each row or bank, the
          chip on the extreme left, slightly separated from the data bits, is the
          parity bit chip.
         

          Expansion Board Memory
         
          The amount of memory contained on expansion boards varies widely from
          manufacturer to manufacturer.  While the early expansion memory boards
          only contained 64K memory, the current standard seems to be memory
          boards in one of three configurations:  256K, 384K, or 512K.  Most
          memory boards still use the 64K 4164 RAM chip, although use of the
          newer 256K 41256 RAM chip has become more prevalent as its
          availability has increased and unit cost has dropped substantially
          (from $60/chip to $7/chip during the past six months).  The
          introduction of 80286-based computers like the AT has also impacted the
          popularity of mega-memory expansion cards because the 80286 can address
          up to 16 megabytes of RAM, as compared to the 1 megabyte limitation of
          8088-based PCs.








                                            1



          To simplify matters, we will limit our discussion here to those
          expansion memory boards that use the 64K RAM chips.  In general, these
          expansion boards comprise from four (256K) to eight (512K) parallel
          rows of nine 64K memory chips.  The rows are usually arranged
          horizontally, numbered from 1 to 8, and are populated sequentially from
          right to left (row 1 is on the extreme right; row 8 on the extreme
          left).
         

          Memory Error Messages
         
          Now that you know which row is where and its "numeric" position
          indicator, you can begin to isolate which chip may be causing the
          parity error.
         
          If your computer has a memory problem, a memory error message will
          appear on the monitor during the start-up diagnostic (Power-On Self
          Test) or when performing system diagnostics.  This memory error message
          consists of two parts:  a four-digit error code followed by the numbers
          201, e.g. 3040 201; and either a PARITY CHECK 1 or PARITY CHECK 2
          message.
         
          A PARITY CHECK 1 message indicates that the memory error was detected
          on the system board memory; a PARITY CHECK 2 message identifies a
          memory error on a memory expansion board.
         

          PARITY CHECK 1 -- System Board Memory Errors
         
          The first number of the memory error code indicates which 64K bank of
          memory is involved.  On PCs with 256K system boards, this can be rows
          0, 1, 2, or 3.  On 64K system board PCs, the number 0 represents the
          entire 64K bank of 36 16K chips.
         
          For PCs with 64K system boards, the second digit can be 0, 4, 8, or C,
          and points to the 16K bank within the 64K which is failing; 0 is row
          0, 4 is row 1, 8 is row 2, and C is row 3.  In contrast, for PCs with
          256K system boards, the second digit of the error message identifies
          the 4K page in the memory chip that is failing; this number is not
          needed to identify the problem chip and should be ignored.
         
          The third and fourth digits represent which bit position (or RAM chip)
          in the 64K row is causing the error condition.  This number represents
          the hexadecimal address of the chip within the row.













                                            2


          Table 1 provides the address for each of the chips on a 64K or 256K
          system board:
         
            Bank    64K    256K  Parity  Bit  Bit  Bit  Bit  Bit  Bit  Bit  Bit
            Number  System  System  Bit    0    1    2    3    4    5    6    7
         
              0      00      0x      00    01  02  04  08  10  20  40  80
              1      04      1x      00    01  02  04  08  10  20  40  80
              2      08      2x      00    01  02  04  08  10  20  40  80
              3      0C      3x      00    01  02  04  08  10  20  40  80
         
                                    M  E  M  O  R  Y      C  H  I  P  S
         
                                        F R O N T    O F    C O M P U T E R
         
            Table 1.  System Board Memory Addresses.
         
          Using the error message example given earlier, 3040  201, we can
          quickly identify the faulty chip as the eighth chip (Bit 6) in the
          first row from the front (Bank 3) of a 256K system board.
         

          PARITY CHECK 2 -- Expansion Board Memory Errors
         
          The procedures for diagnosing errors in memory contained on expansion
          boards is similar to that used for system board memory diagnosis.
         
          The first number of the memory error code indicates which 64K bank of
          memory is involved.  On PCs with 256K system boards, this can be row 4
          or greater; on 64K system board PCs, row 1 or greater.
         
          For both 64K and 256K system board PCs, the second digit is not used
          and should be ignored.  The third and fourth digits contain the
          hexadecimal address (within the row) of the problem memory chip.
         
          Because there are numerous third-party manufacturers of expansion
          memory boards and because each manufacturer may use a different
          configuration and/or bank numbering scheme, the rules for
          identifying errant memory chip addresses for your expansion board might
          be different.  You should check the documentation provided with your
          expansion board as reference for proper diagnosis of expansion board
          memory problems.
         
          For demonstration purposes, however, the following example uses a 384K
          memory expansion board (AST Six Pak Plus), configured with six banks of
          chips, numbered 1 to 6, from right to left.











                                            3


          Table 2 provides the address for each of the chips on the expansion
          memory card.  Notice that the starting address for the rows of memory
          chips is different for the 64K and 256K system boards.  This is due to
          the fact that the expansion board rows begin addressing where the
          system board stops:  for the 64K board, starting address is 1x; the
          starting address for the 256K system board is 4x (x can be any number).
         

          Bank No.          6    5    4    3    2    1
         
          64K System      6x  5x  4x  3x  2x  1x
         
          256K System      9x  8x  7x  6x  5x  4x
          ____________________________________________
         
          Parity Bit      00  00  00  00  00  00      M
         
          Bit 7            80  80  80  80  80  80      E
         
          Bit 6            40  40  40  40  40  40      M
         
          Bit 5            20  20  20  20  20  20      O
         
          Bit 4            10  10  10  10  10  10      R
         
          Bit 3            08  08  08  08  08  08      Y
         
          Bit 2            04  04  04  04  04  04      C
                                                            H
          Bit 1            02  02  02  02  02  02      I
                                                            P
          Bit 0            01  01  01  01  01  01      S
         
                            BOTTOM OF EXPANSION BOARD
         
          Table 2.  Expansion Board Memory Addresses.

          Using the above table, we can see that a 7120 201 error code identifies
          the errant memory chip as the sixth chip from the bottom (Bit 5) in the
          fourth bank from the right (Bank 4) in a 256K system board machine.
         

          Correcting Memory Errors
         
          Now that we have identified the problem chip, we should verify it by
          replacing it with a spare chip and run the diagnostics again and see
          whether the error is corrected.  If no spare chip is available,
          exchange the suspect chip with another one in an adjacent bank.  If we
          have correctly identified the problem chip, the diagnostics will
          display a different memory code -- that of the location where we put
          the suspected chip.
         
          If, however, the error code continues to identify the original
          location, a problem may exist with the socket and you should contact
          your dealer for assistance.


                                            4


          If the system board or expansion board switches are not set properly or
          a chip is missing, the bit position in the error code may be AA, FF,
          55, or 01.  If you are experiencing problems with more than one memory
          chip, the bit position code displayed will be the sum (in Hexadecimal)
          of the problem chip locations and consequently, will not match any of
          the values in Table 1 or 2.  When this happens, the resultant error
          code could be any number from FF to 00.  Diagnosis of the errant chips
          will involve a trial and error process of switching several chips from
          the identified row to an adjacent row.
         

          Reseat Chips Before Switching
         
          Before switching chips in the "suspect" row, however, remove all chips
          and reseat them in their sockets.  Run the diagnostics again.  Because
          many parity problems are due to poor contacts between chips and
          sockets, this trick may eliminate the parity error.  RAM chip failures
          are rather rare.
         
          The most difficult parity error or memory error to locate is one which
          occurs "intermittently".  For example, heat generated by expansion
          boards, disk drives or other add-ons may cause a memory chip or some
          other memory-related component to shift sufficiently to break the
          electrical contact.  You may never find this particular problem since
          the same set of conditions may not be duplicated exactly during
          diagnostics.
         

          A Simple, Do-It-Yourself Remedy
         
          What has been discussed here is a simple method to troubleshoot your
          PC.  If in doubt, professional service technicians have the tools to
          diagnose memory problems instantly.  But performing these simple checks
          yourself can save you money, especially if the cause is a poorly
          socketed chip.



              Diagnosing Memory Problems
                                              by
                                          Arnold Kishi
                                    Hawaii PC Users Group
                      [as updated by Jerry Schneider, CPCUG]

    coded-1 Member

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    Dinho i see say na u own d joint nd u hv don a nice job bt u don come my lodge nd i go run u out coz na me get diz ground(and hmm wethin u write make sense nd long oh see ya later)
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    Babadinho Administrator

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    hehe! Make u remain 4 ur place oo..

    Me just dey do normal posting.

    coded-1 Member

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    dinho iz particular thread dey hard to open with web browser (nd d computer forum dey dull everyone iz intrested in cheatz)na wa oh sha u are hear u would c wht am talking about
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    Babadinho Administrator

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    Na condition wey mtn put people...But just ride on bro...With time all these go normal.

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