Memory board latch diagnostic test behavior

Troubleshooting

Problem

When multiple memory boards are installed in a system, and one memory board has a defective latch sensor, the Memory Latch Test in the on-board diagnostics will incorrectly identify more than one defective memory board.

Resolving The Problem

Source

RETAIN tip: H186774

Issue

Affected configurations

The system may be any of the following IBM servers:

System x3800, type 8865, any model
System x3800, type 8866, any model
System x3850, type 8863, any model
System x3850, type 8864, any model
System x3950 E, type 8874, any model
System x3950 E, type 8879, any model
System x3950, type 8872, any model
System x3950, type 8878, any model
xSeries 260, type 8865, any model
xSeries 366, type 8863, any model
xSeries 460, type 8872, any model
xSeries MXE-460, type 8874, any model

This tip is not option specific.

This tip is not software specific.

Workaround

Run the Memory Latch Test on two and only two memory boards at a time installed either in slots 1 and 3, or installed in slots 2 and 4.

Additional information

The memory latch sensors from the boards in slots 1 and 2 are electrically connected together on the CPU board, so it is not possible for the Memory Latch Test to distinguish which board's sensor is defective. The same is true for the sensors on the boards in slots 3 and 4.

If there are no defective latch sensors on the memory boards, then the Memory Latch Test will run correctly to show that the sensors on the memory boards in all slots are good.

The Memory Latch Test will be allowed to run by the Diagnostics only if memory is configured as Hot Add Memory or Full Array Mirrored Memory. Two or four memory boards are required to be installed for either of these memory configurations to be enabled.

Diagnostics versions 1.05 and earlier permitted the Memory Latch Test to be run regardless of memory configuration.

Because the Memory Latch sensor is only required in FAMM and HAM, Diagnostics versions 1.06 and later disable the Memory Latch Test when memory is configured as Redundant Bit Steering or High Performance Memory Access as described in RETAIN tip H186204 (MIGR-63543).

Please refer to RETAIN tips H185846 and H186204 for information about an issue with weak hotplug sensors in early memory boards, replacement part number 23K4107. The sensors were fixed in FRUs 40K0221 and 41Y3153.

Document Location

Worldwide

Operating System

System x:Operating system independent / None

Older System x:Operating system independent / None

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Tips

Memory board latch diagnostic test behavior - Servers