DC7900 USDT claims support of 2x 4GB PC2-6400S-666 SO-DIMMs but I get POST error (5 beeps/RED LED)

[sallybotz]

In this KB:

https://support.hp.com/us-en/document/c01918674

Socket 1  Socket 2  Total

4GB          4GB            8GB

As well as in the DC7900 Manual here (Pg 34):

"The USDT form factor supports up to eight gigabytes of memory while the SFF and CMT form factors support up to 16
gigabytes of memory."

http://www.hp.com/ctg/Manual/c01549447.pdf

The DC7900 USDT claims to support dual 4GB PC2-6400S-666 SO-DIMMs but after acquiring a pair of Micron 2Rx8 PC2-6400S-666-13-E1 (MT16HTF51264HZ-800C1) SO-DIMMs and installing them in my DC7900 USDT, I get no video, a blinking RED power LED and 5 beep POST error code.  I can swap the pair of Samsung 2GB 2Rx8 PC2-6400S-666 SO-DIMMs back in place and the system operates as usual (I use this PC daily).   SO I know the DIMM sockets are good. 

I'm running the latest Bios (v1.27 from 10-2015) and the latest microcode update as I've upgraded the CPU in this dc7900 usdt to a Core2 Quad Q9505.  

I have also successfully added the same two  Micron 2Rx8 PC2-6400S-666-13-E1 (MT16HTF51264HZ-800C1) SO-DIMMs  to an Acer REVO R1600 system and it boots to Win10 just fine and I've been running it for several hours with 8GB of RAM reported and no issues.   So I think that eliminates most plausibility of the RAM DIMMs being bad.

So looks to me like the DC7900 might not actually support 8GB but I was surprised that the manual *and* support documents would've never been updated after all of these years if that were the case.   I'm not sure what else to try as these two Micro SO-DIMMs meet all the requirements as stated in the HP DC7900 USDT memory upgrade KB noted above:  

For proper system operation, the SODIMMs must be:
● Industry-standard 200-pin.
● Un-buffered PC2-6400 800 MHz-compliant.
● 1.8 volt DDR2-SDRAM SODIMMs.

The DDR2-SDRAM SODIMMs must also:
● Support CAS latency 5 DDR2 800 MHz (5-5-5 timing) and CAS latency 6 DDR2 800 MHz (6-6-6 timing).
● Contain the mandatory Joint Electronic Device Engineering Council (JEDEC) specification.

These DIMMs meet all of these specs per the Micron datasheet here as best as I can tell:

https://www.mouser.com/datasheet/2/671/htf16c128_256_512x64hz-1283564.pdf

Anyone have any idea if these were never actually supported and the documentation is simply incorrect?

Thanks in advance!
SC

[old_geekster]

@sallybotz , welcome back to the forum.

You are absolutely correct in stating that your new memory modules appear to match the specifications that HP states, perfectly.  My first thought was to recommend updating the BIOS, but your computer is too old and HP doesn't provide any software or driver updates for it.  The only other suggestion that I have is, contact the memory manufacturer's Tech Support to see if they can help you.  They are the experts on their products and normally know which motherboards are compatible with them.

Please click the Thumbs up + button if I have helped you and click Accept as Solution if your problem is solved.

[sallybotz]

Will do... thank you for taking the time to write!

[old_geekster]

You are welcome, @sallybotz!  I am always glad to help.