DL585 G7 stuck in Standby mode and will not start up.

Can you get in via iLO? That works in standby, otherwise you could not push the virtual power button. Most of the components on a traditional motherboard are on the SPI board (including the iLO) so that could be faulty.

"system board" is almost eliminated if you take all the PCI cards out although it is the main interconnect. I presume you've tried reseating the processor/memory drawer?

Also have you tried fleabay for the "rather pricey" primary processor board without the tray? HPE don't tend to list that part number, they even put it under mechanical components in the maintenance guide.

https://www.ebay.com/itm/HP-590472-001-Processor-and-Memory-Assembly-for-ProLiant-DL585-G7-/382848413902

There's a SPI for $40 on there too, someone's breaking one up for spares.

Thanks, Andy. Customer sent iLO screenshot. I uploaded it with this comment.
I had not tried reseating the processor/memory drawer but I intend to visit the site tomorrow and will try that.
DL585-G7-iLO--in-Standby.png

Hi,

there might be some BMC activity causing the server not to boot. This would indicate as a blinking green indicator called "BMC ACT". It will prevent the server to boot from standby mode!

If so then pllace a jumper on the RTC reset pins to clear the RTC and try to boot after.

Cheers

You didn't mention swapping the secondary processor board so I assume it is a 2P model. AFAIK you can still have 4 PSUs fitted in it, since you bought two anyway I'd put at least three in as a component may be dodgy and taking too much power. "Server power removed" normally means one PSU went off, there is enough power available to write the log entry though, you don't tend to see that message on single PSU models.

Found another oddity in the manual, not only does it only list the primary board as part of the metalwork it also misses step 0 from this bit...

"Remove the processor memory drawer1.Power down the server (on page 26).2.Release the latches on the release lever.3.Lower the handle, and then extend the processor memory drawer from the server..."

Step 0? Extend server 3 inches to remove the shipping screws some arse didn't take out when they installed it. Had a 300 mile round trip because a junior engineer gave up when HPE's method failed.

So, I replaced both the primary processor and memory system board and the I/O system board for the customer.
Result was that there was only a very slight improvement.
The server attempted to start for ~ 1/2" then back to Standby status.
This activity is repeated about every 9-1/2".
When it is attempting the restart
     Power button turns from amber to green for 1/2"
     Power supplies status light flash on for 1/2"
     Hard drive LEDS flash on then back to off.
The attached videos show these things going on.

Any thoughts on what could be the issue now?
Could the customer have gotten another defective board?
DL585G7-No-Start-Rear.mp4
DL585G7-No-Start-Front.mp4

Most of the components on a traditional motherboard are on the SPI board,  I already mentioned that but you have not replaced it. The iLO / BMC has I2C lanes everywhere. Although it does not contribute to processing power it is responsible for turning the thing on and off.  It lives on the SPI board.

Replaced the SPI but no change.
Replaced secondary processor / memory board but no change.
Cleared the NVM but no change.
Replaced CMOS battery but no change.

Boss has decided to just replace the whole system.

What is the minimum configuration needed to run one of these?

Since it's about 10 years old a high end gaming laptop would out-perform it.