Upgrading CPU in HP Compaq DC7600 SFF

[Zander_Reed]

I am looking to upgrade the CPU from a Pentium D 521 SL9CG to a Pentium D 945 SL9QB.

I read this was the best upgrade on this forum for this computer.

I am on Bios 1.61 and Microcode 1.11. The motherboard revision is 332-2 Rev 0E S31. 
The problem I’m  having is when I install the 945 the computer fails to post and beeps a red light repeatedly 9 times I presume indicating a fault. When I replace the 945 with the original 521 the computer works normally again. 
Looking for advice as to what the issue could be. 

dc7600s/P4-521/33318/4I US

serial no: 2UA63605BS

p/n: RC389UC#ABA

Thanks

Alex

[NonSequitur777]

@Zander_Reed,

You have done some excellent troubleshooting by reinstalling your original Pentium D 521. Because that restores normal operation, it proves your motherboard is functional and narrows the issue down to a compatibility conflict with the replacement CPU.

What the 9 Red Beeps Mean:

According to official HP Compaq dc7600 service documentation, 9 red flashes and beeps specifically indicate a processor recovery or microcode failure. The system physically powers on, but the BIOS halts and rejects the CPU during the earliest stages of the POST sequence.

The Root Cause: Motherboard Revisions:

Whilst your BIOS version 1.61 is fully updated, you are running into a well-documented physical hardware limitation.

When looking at successful Pentium D 3.40GHz upgrades on forums or database sites like UserBenchmark (such as this HP Compaq dc7600 Small Form Factor user benchmark), those systems are almost universally running a later Hewlett-Packard 09F8h motherboard revision.

Your computer is equipped with an early 332-2 Rev 0E motherboard. The physical differences between these board revisions dictate what CPUs can run:

• Voltage Regulator (VRM) Limitations: Early motherboard revisions like your Rev 0E lack the electrical infrastructure and updated voltage regulators required to properly deliver power to 65nm dual-core "Presler" processors (like the Pentium D 945). The later 09F8h revision board was physically redesigned to handle these dual-core power profiles.
• The Silicon Stepping: Your replacement is an SL9QB (C1 stepping). The rare instances where a dc7600 handles a Pentium D 945 usually require the final SL9QQ (D0 stepping) variant, which features updated microcode and tighter power efficiency thresholds that older HP proprietary firmware requires to pass POST.

Recommended Next Steps:

1. Verify the Physical CPU: Check the top heat spreader of the replacement chip to make sure it is genuinely stamped SL9QB and wasn't mislabeled by the seller.
2. Do Not Buy Another Dual-Core: Avoid purchasing another generic Pentium D 3.40GHz (945 or 950). Because your physical motherboard revision is the limiting factor, any true dual-core chip is highly likely to trigger the exact same 9-beep power/microcode fault.
3. The Best Safe Alternative: If you want a guaranteed, noticeable performance boost that works perfectly within the power limits of your specific Rev 0E board, look for a Pentium 4 651 (3.4GHz) or Pentium 4 661 (3.6GHz). These are single-core, Hyper-Threaded processors built on a cooler 65nm process. They will give you the clock speed bump you are looking for without triggering a hardware recovery halt.

Kind Regards,

NonSequitur777

[Paul_Tikkanen]

@Zander_Reed 

I believe that there is only one PD 945 processor sSpec you can install that will work--SL9QQ.

See this discussion where I upgraded the processor in a dc7600 many years ago.

Solved: DC7600 CPU Upgrade - HP Support Community - 578827

[Zander_Reed]

Hi paul

the eBay listing I bought was titled for a sl9QQ but I was sent the SL9QB. In the listing photo you can look at the blurry photo and just make out that the last 2 letters are not the same ( not QQ). As per the other reply I’ll look into some other processors

Alex

[Paul_Tikkanen]

Hi, Alex:

If you read the ancient discussion I posted anyone that installed the SL9QQ processor indicated it worked.

This listing clearly has the SL9QQ sSpec in the photo.

Intel Pentium D 945 3.4 GHz LGA 775 CPU SL9QQ 4M/800 Presler Dual Core Processor 735858190459 | eBay...

It was the lowest overall price of the ones I saw by doing a search.

Sl9qq for sale | eBay

[Zander_Reed]

Hi Paul

yes I read the post earlier today whilst I researched before posting a question on here that’s when I decided to check the microcode version I had before posting a separate question. I didn’t notice anybody say anything about motherboard revisions which is why I included that information 

Alex

[Paul_Tikkanen]

Hi. Alex.

I have no info on that either and since we donated the PC years ago, I can't look up the motherboard revision.

I don't recall anyone in the past indicating that only certain dc7600 motherboard revisions would support specific processors.

If memory serves me right, the only PD 945 sSpec stepping code that was supported by the BIOS and microcode update was the SL9QQ.

Many years ago, there used to be a HP business PC support forum which had a treasure trove of info on the older HP business desktops notebooks and workstations. 

That's where I got the info on the SL9QQ being the only supported PD 945 processor for the dc7600.

Sadly, HP didn't import all of the posts from that forum to this one, and thousands of posts containing valuable info were gone in a flash forever.

I forgot what year they decided the cutoff was, but we lost a lot of good business class desktop and notebook PC info during that merger.

I had joined that forum in 2007-- three years before I joined this one, and the business support forum was around for several years before I joined it.

Cheers,

Paul 

[Zander_Reed]

Hi Paul

The microcode 1.11 on the support page lists both the F64 (sl9QB) & F65 (sl9QQ) as supported so that would suggest it “should” work. 
https://support.hp.com/bg-en/drivers/swdetails/hp-compaq-dc7600-small-form-factor-pc/model/472259/sw...

This is also the processor I purchase: https://ebay.io/m/gIDa6q

I also saw the manufacturer date of the pc stamped on the inside of the case is marked 2006-07-24

Alex

[Paul_Tikkanen]

Yes, based on that information either one should have worked. 

The dc7600 was released to market in Q2 of 2005, so yours was not an early model in the series. 

As a matter of fact, the dc7700 was released in Q3 of 2006.

It's unfortunate you don't have another PC to test that processor in, because IMHO, the processor may be defective. 

[NonSequitur777]

@Zander_Reed,

I agree with Paul's latest assessment. Given your BIOS version 1.61, HP microcode 1.11 listing both processor signatures, and the documented dc7600 configurations with a Pentium D 945, I see no solid evidence that motherboard revision 332-2 Rev 0E is inherently incompatible with the SL9QB.

A defective replacement CPU is certainly plausible, although testing it in another compatible system would be the best way to confirm that diagnosis.

Since the seller advertised an SL9QQ but supplied an SL9QB, I would pursue a replacement or refund rather than purchase another processor at your own expense.

Best of luck getting this sorted out!

Kind Regards,

NonSequitur777