Use the FB-DIMM Fault Locator button to identify faulty FB-DIMMs.
Note - The location of this button is shown in FB-DIMM Fault Locator Button on the Motherboard. It is marked SW6500.
See Remove the Top Cover.
This will cause an amber LED associated with the faulty FB-DIMM to light for a few minutes.
Note - The FB-DIMM Fault Locator button is near the left edge of the motherboard (as viewed from the front panel). It has the label SW6500 in the following figure.
Figure 66 FB-DIMM Fault Locator Button on the Motherboard