16gb upgrade on old Asus M4A785-M

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Ceph92

Limp Gawd
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Sep 17, 2019
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I have an Asus M4A785-M which is AM3 with DDR2. I recently tried to upgrade its memory from 8gb to 16gb and am running into problems with various memory testers (eg memtest86+). Maybe some of you hardware grandpas have some wisdom to share.

The configuration is just the mobo, phenom II 960T (4x), various mem configurations, no other hardware. Firmware is latest, v1101 - no mention of 16gb limitation or fixes in documentation or bios patches.

Observations:
  1. the exact samsung sticks are in the "tested" list per Asus
  2. configurations that work: 4x2gb, 2x4gb + 2x2gb
  3. configurations that do not work in any arrangement: 4x4gb
  4. all sticks tested individually - ok
  5. each slot tested individually - ok
  6. default memory settings in BIOS
  7. tried a variety of dual channel and interleaving settings - no obvious effect
Thanks for any help.

https://www.asus.com/Motherboards/M4A785M/
 
This thread should probably be in the motherboard forum. If a mod can move it, that would be fine with me.
 
You may need to increase RAM voltage and \ or manually lower ram speed \ increase timing to get all 4 sticks to run without error.
 
https://www.asus.com/Motherboards/M4A785M/HelpDesk_QVL/

Download the
Memory / Device Support file and review your memory type.

Not all memory types support 4 dimm slots on this mobo.

4 Dimm :
• A*: Supports one module inserted in any slot as Single-channel memory configuration
• B*: Supports one pair of modules inserted into eithor the blue slots or the black slots as one pair of Dual-channel memory configuration
• C*: Supports 4 modules inserted into both the blue and black slots as two pairs of Dual-channel memory configuration
 
deaedius said:
Not all memory types support 4 dimm slots on this mobo.

4 Dimm :
• A*: Supports one module inserted in any slot as Single-channel memory configuration
• B*: Supports one pair of modules inserted into eithor the blue slots or the black slots as one pair of Dual-channel memory configuration
• C*: Supports 4 modules inserted into both the blue and black slots as two pairs of Dual-channel memory configuration
Click to expand...

Thanks for finding that. It does show that 4 DIMMs are supported for M378T5263AZ3-CF7, though.
 
Kardonxt said:
You may need to increase RAM voltage and \ or manually lower ram speed \ increase timing to get all 4 sticks to run without error.
Click to expand...

I'm taking a look, thanks. I actually haven't done this stuff in many years and when I did I didn't play much with timings.
 
yeah id try the voltage, didn't think of timings but that might help too. put in whatever config works and bump the voltage by 10%. save shutdown and add the other sticks. see if that helps. if not, raise the timings a notch.
 
So I tried 333mhz which works fine. There aren't fine increments for ram clock, it must be a multiplier of some other clock that does...

6-6-6-18 is as loose as the timings get on that board, so I've got nothing to play with. 6-6-6-18 is default for 400mhz, and 6-5-5-15 for 333mhz.

Setting the memclk to 400mhz explicitly made the system unbootable (!?).

Setting the ram voltage to 1.9v explicitly (from 1.8v default I assume) also made the system unbootable.

Is 3400MB/s - 3700MB/s too low for this system? That's the range memtest86+ (v4.20) is reporting.
 
Last edited:
sounds about right but I has been a loooooooong time since I touched ddr2.
 
I changed the base clock from 200mhz to 220mhz, which I think would raise the memory to 366mhz. It boots but completely fails memtest86+, as if it were back running 400mhz
 
IIRC 333mhz = ddr2 667 = pc5300. I don't think you will have any trouble, it's essentially just running 1 step down from its rated speed.

As with the others, I haven't touched this stuff in ages so could be wrong. If you were concerned about the speed you may want to take a look at hypertransport and north bridge multiplier \ voltages as well.

It's worth mentioning that 4gb sticks were pretty exotic and that mobo was pretty bottom of the barrel, 333 may be the best it gets. I was surprised to see any 4gb sticks on the QVL to be honest.
 
Kardonxt said:
IIRC 333mhz = ddr2 667 = pc5300. I don't think you will have any trouble, it's essentially just running 1 step down from its rated speed.

As with the others, I haven't touched this stuff in ages so could be wrong. If you were concerned about the speed you may want to take a look at hypertransport and north bridge multiplier \ voltages as well.

It's worth mentioning that 4gb sticks were pretty exotic and that mobo was pretty bottom of the barrel, 333 may be the best it gets. I was surprised to see any 4gb sticks on the QVL to be honest.
Click to expand...

How do NB & HT voltages affect RAM?
 
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