HP z840, no boot, no beeps after plug into bottom PCIe 1x slot

[connerdailey]

I am baffled as this has now happened twice to me. I have an HP z840 workstation with 2 CPUs installed. Of the 7 PCIe slots on the motherboard, I had 1-6 populated with devices, running fine for weeks. I go to install a device into the bottom (slot 7) slot, I now get no boot. No beeps. Just 30 seconds of fans before shutdown.

This happened to me once before, I didn't connect the dots then, and figured I had a faulty motherboard. I replaced it, worked fine until I tried the bottom slot again, now same symptoms.

I reset CMOS button, no change. Power supply shows green button.

I just cannot fathom that this board destroys itself upon use of the bottom slot. Does anyone understand what is happening?

[TheOldMan]

Here is a tech document outlining the slots for the Z840 workstation.   Page 10 indicates the possible reason slot 7 acts differently than the rest.  Slot 7 is PCIe2 x1 connected directly to the chipset.  All of the other slots are connected thru the CPU controllers, and you can see the which one is controller by which CPU.  The device currently in slot 7, IMHO,  is not supported for that slot.  Depending on what that device is, and the others as well, you might get it to work by swapping devices around in the other slots.

https://www.manualslib.com/manual/928210/Hp-Z840-Workstation.html?page=10#manual

[DGroves]

power off and remove power cord, now press power button till beeping stops and power light is off

open case remove all addin cards except for video

then either remove the cmos battery for 5min then reinstall or press the cmos reset button for 10 sec

close cover, connect power cord and power on system should start if so enter bios set time/date only and reboot again

since you failed to state the card being installed and what is currently installed in each slot  i can't make any specific comments about this in regards to the z840 but i suspect the system is unable to relocate any free system resources necessary to configure the last card

[connerdailey]

Thanks for the swift replies.

I followed you advice closely, but the only change was faster fans. About 30 seconds fans on, then power goes off. No beeps, no screen, no boot. I had a Quadro K620 in slot 2 for video out for this test. This is exactly what happened last time as well.

My system has 2 E5-2699a v4 CPUs installed, all RAM slots populated with 256GB total of memory.

Before this, I had in the top slot a Quadro K620 for display output, and in slots 2-6 I had in each a Quadro P4000, 105W TDP.

Since with the 1125W power supply, HP quotes support for up to 3 225W graphics cards, I would think 6 105W graphics cards should not be a problem, along with some PCIe 6pin to dual 6pin adapter cables. So I got one of these PCIe 1x to 16x riser cards, and connected it to the 1x slot, with the riser card powered with molex, hoping to run now 6 of these cards at once. I don't care about PCIe bandwidth. I never even got the chance to even ramp up the power draw, as with the riser connected for the first time, no boot followed after, so this doesn't seem to be a power issue.

Now it seems like I have bricked this board by attempting to do this. I cannot understand why this would happen, as far as I can understand, there should be nothing wrong with this. There is some language in the service manual stating that the 1x slot is not supported for a certain card if a double wide card is in slot 6, but other than that, I don't see why using this slot would brick the board.

Is there even anything else I can do?

[SDH]

1. New motherboard, again.

2. Don't do that again.

3. You mining with all those cards?

4. I'm quite sure HP never certified your plan as "supported".

[connerdailey]

1.) Figured that

2.) Figured that

3.) No, this is a research machine that is faster the more GPU power I throw at it.

4.) I didn't expect official support for this, but I did expect PCIe lanes and power connections to work as they should. I wouldn't expect this not to work on any generic motherboard, so why not this one? Even if it didn't work, I wouldn't expect to brick a board just because I used a slot with a device designed for that slot.

[TheOldMan]

It would seem the adapter card is not compatible with the slot #7 or the extra load from the device is causing a motherboard burn-out.  Perhaps consider not using slot #7 in that manner, since it is different than the rest of the slots.

[DGroves]

The HP z8xx series of workstations use a multirail power supply, not the more common single rail design that consumer systems now use

by trying to use 6 120 watt video cards you have overloaded the z840's GPU power supply rail and possibly other rails

read the supplied HP docs, the z840 1125 watt supply can power up to two 150 watt video cards if "certain" conditions are met ( or one 300 watt card) note that the 150 watt spec is the total power draw of the card, not the GPU pwr rail

HP only certified up to 4 video cards in SPECIFIC COMBINATIONS on this system

google differences between multirail vs single rail power supply for details

https://help.corsair.com/hc/en-us/articles/4415065357069-PSU-What-you-need-to-know-about-single-rail...

[connerdailey]

But the service manual specifically states the following:

I was trying to use 6 105W cards, not 120W.

Even if it was the case that you have stated, this still wouldn't make any sense, as the power draw was never even ramped up to a max level, the board failed to boot with the configuration just connected. This is why I stated that this doesn't make sense as a power issue.

[SDH]

Conner,

In my mind your frying of 2 good motherboards has proven your idea is not a valid one. Nowhere in the manual does HP say the logic you're using will work. You have 3 PCIe x16 slots but are all 3 of those rated the same in power draw? And, into what slots did you put the other 3 video cards? Are each of those slots rated for the level of load you put on them? 6 x 105W does not equal 2 x 300W when the 6 cards are going into 6 different slots, a number of which are rated for different loads.

Are you aware that most PCIe x16 slots can feed 75W up into a card but that other PCIe slots cannot, and that some PCIe x16 slots can only feed less that 75W up into the card? The motherboard traces feeding power to PCIe slots are of different size based on their design engineering (so you might be melting one trace but not another). It is not simple.