4 red LED flashes (4 short beeps)

[block306]

I have the Z400 for the last 4 years. Have been working great.

Couple of weeks ago, one of the hard disks connected to the system was faulty. I opened up the chasis to remove the faulty hard disks. When I put everything back, the workstation went into the 4 short beeps (4 red LED flashes for me as the front speaker is not working). I have followed the diagnosis on page 196 of this guide to determine the problem:

http://h20628.www2.hp.com/km-ext/kmcsdirect/emr_na-c02589908-1.pdf

At first I thought it was the psu since the psu fan was not spinning. I managed to buy a good refurbished psu and connect it to the setup. Same prblem- 4 short beeps. I went through the steps again, even removing the cmos button battery for over a day (to erase its memory). Same problem persists.

I am now suspecting the motherboard may be compromised. Before I embark on searching for a replacement (which may be a challenge, considering the age of the workstation), is there anything else I should try??

Thanks.

[SDH]

The 4 beeps/flashes indicate a fault that is getting back to the power supply, and it can be from any connection.  It is a PITA to figure out, but you can debug this by disconnecting everything (down to that faulty speaker, where I'd start first), and I mean everything, and then slowly start adding things back in.  You want the power supply disconnected from everything and everything disconncted from the motherboard.

Any connection that the power supply perceives as a short or causing a too-low resistance event will trigger this.

So, set aside an afternoon and get out your flashlight and take some notes..... I have done this and generally have found it is not the motherboard at fault.......