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June 22nd, 2025 17:35
Dell T5400: FB-DIMM full length heat spreader
I got an old T5400, with 6 sticks of DDR2 ECC FB-DIMMs (4x1GB+2x2GB). Brought 4x4GB DDR2 ECC FB-DIMMs, with full length heat spreader and look just like those FB-DIMMs in the machine.
POST complained about those are NOT full-length heat spreader DIMMs :(.
Any suggestions on how to overcome this?
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qili00
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July 7th, 2025 19:32
I think I have found the solution - undocumented in the user manual: you will need to reset the RTC after the memory modules are repopulated.
I put in 8x4GB sticks, reset the RTC jumper (next to the coin battery). Boot it up. 8x4GB detected, and 8x4GB usable, in the BIOS / Windows / Linux.
Hope this helps someone down the road.
qili00
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July 5th, 2025 23:58
Got 8 sticks of 4gb ddr2 fb-dimm memory. Boot up just fine. Looks like what I had was faulty.
qili00
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July 6th, 2025 00:24
But I have a new problem.
The board has 8 memory slots. Slots 1...4 are white and slots 5...8 are black.
The manual calls for 4 matching pairs to be installed in slots 1...4 and then 5..6.
When all 8x4gb identical sticks are installed in slots 1...8, they are all correctly detected but the system shows only 8gb of memory installed, dual channel, in bios and in Windows 11 and Linux (all 64bit).
When 4x4gb sticks are installed in slots 1...4, all 4 sticks are detected in bios but only 4gb, single channel, are usable in bios and in Windows 11 and Linux.
System wouldn't boot if 4x4gb are installed in slots 5...8.
qili00
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July 6th, 2025 00:26
4x4gb are installed in slots 1..2, 5..6, 16gb is detected and 16gb, dual channel is usable,
Installing any additional sticks in slots 3..4 or 7..8 I'm back to 4gb or 8gb usable.
qili00
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July 6th, 2025 00:27
Installing 1x4gb gave me 4gb of usable space.
Installing 2x4gb gave me 8gb of usable space.
qili00
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July 6th, 2025 12:08
The only common theme here is that ram sticks in slots 3..4 and 7..8 can be detected but don't contribute to usable memory for some reason.
However, this very machine used to run an 8gb configuration successfully: 4x1gb in slots 1..4, and 2x2gb in slots 5..6.
Scratching my head 😞