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How To Repair RAM

The RAMCHECK LX memory tester is a powerful tool for repairing defective DIMM and SODIMM modules by
pinpointing the defect and identifying the defective chip. Of course, the first thing you need to do is test the suspect module to confirm that it is faulty. This takes just a few seconds with RAMCHECK LX.

RAMCHECK LX will quickly identify the module's speed, size and type, and give a pass/fail message. RAMCHECK LX error messages also generally identify the relevant pins (circuit connections to the test socket) of the module being tested which are associated with the problem. It is designed to provide you with explicit error data to enable you to identify the defective component(s) on the module.



RAMCHECK LX DETAILED ERROR MESSAGES
DDR3 data
                              error RAMCHECK LX reports data bits error in each rank explicitly, using two lines. The first line is the "byte" view, indicating errors within byte 1 to byte 8 for an x64 module. You can scroll left or right, as the second line shows the individual bad bits within the bytes highlighted in the first line. In this example, DQ31 of RANK 2 is bad.  
  Use F3/F4 to get more detailed error information
DDR3 DQ
                              error The first press of button F4 replaces the module size speed info in the bottom line with the explicit DQ error (DQ31 in this example). It also indicates the module pin number which is connected to this DQ line. As you will see below, knowing the DQxx error tells you which chip is bad! 
DDR3
                              address error for DQ Pressing F3 returns to the previous screen, an additional press of F4 drills down into more information. Here it tells you the address where the error was detected. 
DDR3 data
                              error screen 4 Press F4 again to see the Row/Column component of the address at which the error was detected. 
DDR3 data
                              error screen 5 Press F4 again to see the hexadecimal error in a 64 bit double word. 
DDR3 data
                              screen 6 You can also see which test type found the current error. In this example, the error was found by an array type test that scans the memory array.  
DDR3 data
                              screen 8 Here it shows the data in the S control line (S=2 means that S0=0, S1=1, for RANK 2).  The B2/0 indicate RANK 2 with bank address  BA=000. 

When RAMCHECK LX reports a data bit error, it tells you which DQ bit/s are bad and it also identifies the relevant pins (circuit connections to the test socket) of the module which are associated with the bad bits. You can remove the module from the socket and review the Test Log of the last memory test by pressing F4 during Standby. Easier still, use the RAMCHECK PC interface to identify faults (see below).



Spotting the Defective Memory Chip

Every memory module has chips that are arranged from left to right (when you look at rank 1) in accordance with the bits (each bit has a DQ number) of the module. RAMCHECK LX data errors clearly identify the DQ bit/s which are bad and it tells you which chips are being used. You can easily identify the bad chip from the RAMCHECK LX data errors as follows.

The most popular modules (regardless of size and DDR1/2/3 type) use individual chips with x8 data width. Therefore, x64 module uses 8 such chips per rank and ECC (x72) uses 9 chips. The first chip on the left always connects to DQ0-7. The second chip connects to DQ8-15, the third chip from the left connects to DQ16-23, and so forth. The ECC chip (for DQ64-71), if available, is placed in the middle of the module as the 5th chip, as shown in the following drawing.

Module with
                x8 chips
For example, 
if RAMCHECK LX reports the error DQ17 bad, you know it is the third chip (DQ16-23)  from the left. If you test a dual rank module (one that has chips in both sides), you need to follow the RANK number reported by RAMCHECK LX. If it is RANK 2, you need to turn the module over and follow the chips in a reversed order - DQ0-7 of RANK 2 will be the first chip on the right side when you look at the back side of the module.  

Similarly, an x64 data width module (regardless of size) that uses x16 data width individual chips, has 4 chips per rank. The first chip on the left always connects to DQ0-15. The second chip connects to DQ16-31, the third chip from the left connects to DQ32-47, and so forth, as shown in the following drawing. So if for example RAMCHECK LX reports the error DQ30 bad in RANK 1, you know it is the second chip.  


Module with
                x16 chips

If RAMCHECK LX reports DQ30 in RANK 2, the bad chip will be the second from the right when you look at the back side of the module, as shown here

RANK 2 x16
                chips

Server ECC x72 modules with x4 chips also have a regular orderly arrangement and your technician can convert the RAMCHECK LX error report to identify the chips. Such module are typically include 36 chips, for two RANKS. The following drawing illustrates how the chips are connected. The chips marked D0-D4, D10-D13, D18-D22 and D28 to D31 comprise RANK 1. The chips marked D5-D9, D14-D17, D23-D27 and D32-D35 comprise RANK 2 of the module. The vertical chips pairs (e.g D0 and D5, D1 and D6, etc.) connect in parallel, and control by module control lines S0 (for RANK 1) or S1 (for RANK 2).

Chips D0 and D5 connects to DQ0-3 in the front of the module. Chips D18 and D23, which are placed directly beneath D0 and D5 on the back of the module, connect to DQ4-7. Continuing in this order, chips D1 and D6 connect to DQ8-11 on the front side of the module. Chips D19 and D24 on the back of the module connect to DQ12-15, and so on. Finally, the last chip pair in the front side (D13 and D17) connect to DQ56-59 while the chips D31 and D35 beneath them on the back side of the module connect to DQ60-63.

Module with
                x4 chips 

Server ECC x72 modules with x4 chips and only one rank are much less popular. The arrangement of the chips is similar to the above drawing, with the omission of chips D5-D9, D14-D17, D23-D27 and D32-35. More explicit drawings of modules is available in the JEDEC web site, but the above drawing should be sufficient to determine the chips in most cases.





Now that you know where the defective chip is you'll have to replace it. Only a technician with component-level repair expertise can repair a memory module. The required soldering/ desoldering equipment is relatively complex, especially with modules and cards made with extremely thin Surface Mount Technology (i.e., devices with BGA or TSOP RAMCHECK LX DDR2 memory tester now availablechips). You will need a good deal of practice with desoldering techniques. Nevertheless, a few minor problems, which are identified by RAMCHECK, can be repaired with simple tools. A short between an adjacent pin may be caused by a small piece of metallic debris, which is stuck between two chips. You "repair" the module in this case with an Exacto knife or a watchmaker's fine screwdriver by simply removing the debris. If you use RAMCHECK in the production shop, you should be able to easily replace the module's components.

Repairing memory does involve a fair amount of work, but as companies around the world have discovered with RAMCHECK LX, it can be a lucrative business.

Other Resources:
New structure analysis for RAMCHECK test results - important for memory module repair.
How to Desolder
Desoldering tools




Other articles in this series:


How to repair RAM

Selecting a memory tester

How to test memory

Quality of Memory - Remarked versus marked, brand name vs no name

What is the SPD and how to program it

Evolution of memory

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