Scratch101
1 Copper

Precision T7500 strange Pb7 message

I've had and loved my Precision T7500 for years now, unfortunately I have an issue that, no matter what I do, I can't seem to get rid of. Here's the story.

About a month ago I was attempting to install Linux on it and I was having difficulty (I later discovered the issue there was a SATA card that's not Linux compatible). As I tried different versions of Linux and they kept failing I needed to restart quite a bit. As I did, I noticed one time I got what I would later come to realize is a Pb7 Code  (http://www.dell.com/support/article/us/en/4/SLN288786/precision-t3500-t5500-t7500-workstations-diagn...). I continued to work on this for maybe another hour, then I got the Pb7 code and it wouldn't go away.

I started to panic a bit and I began disconnecting Hard Drives until I had just the system drive connected. That changed nothing. I removed all my PCI-e cards which also changed nothing. Then I reconnected the cards and went searching for answers. Based on what I read I thought that maybe I damaged my system board, so I purchased one. Once installed, I got the same error code. I then decided to pull the riser board (which I hadn't done until that point) and it booted immediately. Based on that I did additional testing. I put all the RAM on the motherboard and it booted just fine. I then swapped CPUs and it booted fine. I assumed that this meant that the Riser board was damaged so I replaced it and repopulated everything correctly. When booted I got the same Pb7 message. I then assumed that my power supply was bad, so I replaced it. That also did nothing. I did an extended Memtest check on my full set of RAM and it passed.

That brings me to where I am now which is to say, very confused. I want my computer back and running at full speed but I don't really want to spend more money on it without getting input about what the issue might be. It runs fine with 1 CPU, but always fails with the mentioned code when the riser board/second CPU's installed. I'd greatly appreciate any thoughts or suggestions.

For the record, my system specs are as follows: Before the problem I had 2x Xeon 5675 and 12 GB RAM with EVGA Geforce GT 750. I'm currently running half of that, so a single 5675 and 6 GB RAM.

0 Kudos
9 Replies
Community Manager
Community Manager

RE: Precision T7500 strange Pb7 message

Hi Scratch101,

Thanks for posting.

It would appear that your BIOS is affected:  http://dell.to/2rLmavr

You could try to re-flash the BIOS to correct the problem, otherwise, it would mean a motherboard replacement.


Dell-Robert P
Social Media Support
#IWork4Dell
To help us troubleshoot, please send us the Dell service tag number via a private message
Would you like to be a Dell Community Rockstar?


0 Kudos
Scratch101
1 Copper

RE: Precision T7500 strange Pb7 message

As I mentioned, I did replace the motherboard (in fact that's the first thing I replaced) and it has the same problem as before. In fact the only things I didn't replace are  the CPUs and the RAM. I suppose it is possible that the board I purchased is also bad in the same way but I find that less than likely.

There must be something else...something that I haven't replaced or something that I'm missing. I'm not sure what that would be at this point, though.

Again, I have replaced the motherboard, riserboard, and power supply. It boots/runs fine with no riserboard in all instances. What am I missing?

0 Kudos
RoHe
6 Thallium

RE: Precision T7500 strange Pb7 message

I'm confused... What OS are you running that works with 1 CPU but not when riser and second CPU are installed?

Are there any BIOS settings you have to change when the riser and second CPU are installed?  

Have you tried clearing BIOS? Reboot and press F2 to open BIOS setup. Copy (or photograph) all current settings, just to be safe.

Then power off and unplug. Press/hold power button for ~15 sec. Open case and remove motherboard battery. Press/hold power button for ~30 sec. Reinstall everything exactly the way it was when it last worked with 2 CPUs and all RAM installed. Now reinstall the battery. Close up and see if it boots with only mouse, monitor and keyboard attached.

Ron

   Forum Member since 2004
   I am not a Dell employee

0 Kudos
Scratch101
1 Copper

RE: Precision T7500 strange Pb7 message

I apologize for not making this clearer to begin with. I did attempt to but I've done so much

This issue arose when I was testing Linux and having a difficult time installing it. I did discover the problem with Linux was an unrelated SATA card. That was just testing as I wanted to move to Linux for certain things. I was running the same install of Windows 7 when the issue first happened but it doesn't matter since it acts the same under Windows 10. In short - it won't boot with any OS when both CPUs are installed but it will boot to whatever I want with one CPU.

I have now tried clearing the Bios, it had the same result...I get the Pb7 error when I attempt to boot with both CPUs but it boots and runs fine with a single CPU. This has happened with 2 different motherboards so I'm guessing that the issue has nothing to do with the motherboard or the Bios. That said I still have no clue what the issue might be.

0 Kudos
RoHe
6 Thallium

RE: Precision T7500 strange Pb7 message

The riser board requires several cable connections to be made, eg a power cable from motherboard to riser board, and cable from riser heat sink fan to riser board...

Sure you're connecting all of them correctly?

Check the instructions in the manual (page 86) for details of those cables and connectors.

downloads.dell.com/.../precision-t7500_service manual_en-us.pdf

And are you following the rules to populate RAM when the riser is installed (page 17)?

EDITED: And are you seating the riser correctly in its 2 slots?

Ron

   Forum Member since 2004
   I am not a Dell employee

0 Kudos
Scratch101
1 Copper

RE: Precision T7500 strange Pb7 message

I'm sure that the riser board was connected correctly when this originally occured and I'm sure it is now. As for the RAM I learned my lesson on that  after my first install of the riser board. For that it gave me a little message saying that the RAM configuration is sub-optimal so I learned quickly there.

As for seating the Riser board properly, I saw damaged pins on riser boards online before I purchased mine so when mine arrived I was (and have been) quite careful when installing it.

That said, it had been running for years when I first started getting this error code with both CPUs.

0 Kudos
RoHe
6 Thallium

RE: Precision T7500 strange Pb7 message

Have all my suggestions been done with new or old motherboard? Did you double-check to see if you still get pb7, no matter what you try?

pb7 is "BIOS not execution". Surprising you'd get same code if you changed the mobo. Do you know the new mobo is good, even if it boots with only 1 CPU?

What if you use the bare minimum amount of RAM to populate the mobo and riser, but still using a supported RAM config?

You replaced mobo, riser and PSU, removed PCI-e cards and disconnected non-boot hard drives. So that probably only leaves the boot hard drive, video card, and front panel circuit board, assuming the new board is ok.

Running out of other ideas...

Ron

   Forum Member since 2004
   I am not a Dell employee

0 Kudos
Highlighted
17RSE
1 Copper

RE: Precision T7500 strange Pb7 message

I've got same PB7 error. It's a T5500 with two X5690 and 48GB ram. Everything works with one CPU, but not when the second CPU (riser) is present. I've tried swapping CPU, both worked in the main motherboard, so it's certainly not CPU.

Check this post. en.community.dell.com/.../19589143

The last two seem to suggest that there is a mechanical issue. Can someone from Dell please confirm?

0 Kudos
Scratch101
1 Copper

RE: Precision T7500 strange Pb7 message

Well, my issue has been resolved.

I spoke with a friend whose thoughts I trust in computer matters. She suggested that, in spite of the fact that the computer will boot with both CPUs in individually, there could be an issue that would make them not match. She pointed me to a thread (which, for whatever reason, I can no longer find) where someone else described exactly what she had suggested.

I wanted to follow through but was delayed due to health issues. I recently ordered the replacement CPUs (I decided to upgrade while I was at it) and everything is working swimmingly now.

So folks who get this message please note that you can run an individual CPU (and you can swap them as I did) and still have things work fine but together they will fail and give this message every time. That means something small is busted in the CPU itself. It's not preventing it from booting but it prevents them from matching perfectly so that they will no longer run together.

I have to admit, I was surprised at this since CPUs are normally the last thing to go bad in a computer but it can and does happen.

Anyone who's having problems like I was (17RSE, for example) this may well be your problem.

0 Kudos