R640 DIMMs failed the memory test

Hi WINSF,

Based on the details you've shared, the most probable cause of this issue is as follows.

The Critical / No memory found / All channels have been disabled due to all DIMMs failed the Memory Test message means the BIOS found a DIMM on the memory bus but could not initialize/train it, so it disabled all channels and halted POST.

With a single SNPTFYHPC/16G (16 GB DDR4‑2933 RDIMM, 2Rx8) and BIOS 1.4.9 on a used PowerEdge R640, the most common reasons are:

1. Memory speed not supported by the installed CPU/BIOS
• 2933 MT/s memory is officially supported only with 2nd‑Gen Intel Xeon Scalable (Cascade Lake) processors, and even then, an early BIOS such as 1.4.9 may not initialize newer DIMM SPDs correctly.
• If the R640 has a 1st‑Gen Xeon Scalable (Skylake) CPU, the official max is 2666 MT/s; the 2933 DIMM may not downclock far enough to POST.
2. Wrong DIMM slot
• With a single CPU, the first DIMM must be in slot A1 (the white‑tab socket of Channel 0). Installing it in A7–A12 or any B slot can cause exactly this “no memory” behavior.
3. Physical / motherboard issue
• If two different 2933 sticks both fail after reseating, the DIMMs, the CPU socket, or the DIMM slot could be bad.

 Resolution steps

1. Install the DIMM in the correct slot
• Power off, drain flea power, open the server.
• Place the single 16 GB DIMM in A1 (white release tab, first slot of CPU1). Do not use any B slots unless a second CPU is installed.
2. Check the CPU installation
• Reseat the CPU and verify the heat sink/retention is evenly tightened.
• Inspect the CPU socket for bent pins or debris. A bad CPU‑to‑memory path can cause every channel to fail.
3. Clear NVRAM / reset BIOS
• Use the NVRAM_CLR jumper on the system board (or remove the coin‑cell battery for a few minutes) to force BIOS defaults. This rules out any manually set memory timing/voltage that could prevent training.
4. Test with a known‑good, lower‑speed DIMM
• If possible, try a DDR4‑2666 or DDR4‑2400 Dell‑certified RDIMM (16 GB, 2Rx8) in A1.
• If the lower‑speed DIMM boots, the 2933 module is incompatible with the current CPU/early BIOS.
• If it also fails, the board/CPU/DIMM slot is the more likely culprit.
5. Update BIOS / iDRAC
• If you can boot with a lower‑speed DIMM, update the R640 BIOS to the latest release from Dell Support, then retest the 2933 module.
• If the installed CPU is Skylake, you will need to use DDR4‑2666 modules; 2933 MT/s will not run at full speed on that generation even after a BIOS update.
• If the CPU is Cascade Lake, the 2933 module should work after a BIOS update.
6. Verify CPU model / memory density
• Confirm the CPU is Cascade Lake‑based if you intend to run DDR4‑2933.
• Also check that the DIMM is not a 16 Gb chip‑density module; Skylake does not support 16 Gb DRAM density (see Dell KB 000219510).

Bottom line

The SNPTFYHPC/16G part is generally a valid R640 DIMM, but with BIOS 1.4.9 and a possible Skylake CPU, the 2933 MT/s speed is the most likely trigger for the “all DIMMs failed memory test” error. Start by reseating the DIMM in A1, reset NVRAM, and—if you can borrow one—test with a DDR4‑2666 Dell RDIMM. If the lower‑speed module POSTs, update the BIOS; if the CPU is Skylake, swap the memory for 2666 MT/s modules. If no known‑good module works, the CPU socket or system board is suspect.

Regards,

DELL-Bridjet V

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