Tuesday, April 19, 2016

Just a Cable (Part 1)

Subtitle: A PC Bench

My quest to build another Ultra Reliable, economically priced Home Firewall has been met with some challenges in the last 2 weeks.

Essentially DOA Hardware.  And DOA is an acronym for Dead on Arrival or in my case Dodgy On Arrival hardware :-)

You are Just not going to Believe It
The centre of the problem was a very weird error

I built a new computer

With a SSD hard disk.

I found that when only 1 SSD disk was connected, to any of the 4 SATA ports,  PC would not start, Power Supply Starts and Stops repeatedly

PSU Start Stop is a symptom for Electrical Short

Modern PSU are intelligent to shut down on short, wait a while, then power back up.  Hence the observed behaviour.

When a second non SSD, i.e. Spinning Disk was added to any other SATA port, the Motherboard booted up fine.

I know.  Bloody unbelievable. 
3 different PSU tried.
Changed Memory
Tried different Keyboard/Mouse

Behaviour repeatable.

The Good News
As of today, some 21 days later, and a long time to wait to resolve the problem, all is well.  I'll document it later.  Here I want to show you how to build a PC test Bench

The PC test Bench
Now you can buy a special "Open Air" PC case, which is really just an open Chassis onto which you can put your new Motherboard or peripheral etc.

But most of us don't have the space, or want to dedicate resources to this setup.  So here is what I recommend as a minimal test bench

- A Table
- A Plastic Sheet
- A Power Supply
- A Spare SSD hard disk
- Connection to a Monitor
- A special Power cable!!

This cable  took about 2 weeks to arrive from China.  It cost 2 GBP.  Now that is a bargain

 Consult the manual to find where the Power On header is

The PC Reset or Power Switch in 2016 works by quickly shorting 2 contacts.  It should not  (like in the old days) remain shorted permanently.

So this cable has a single button, wired to a plug called Reset.   You can thus use this either as a power on button or a reset button. Initially connect this to the Power-Reset pins on the motherboard, for use as a power button.

The other connectors on this cable are marked Power+ Power -, HDD+ HDD-  and drive 2 LEDS.

There is another way
Without the cable you can take a screwdriver and just for an instant, touch, i.e. short the Power and Ground pins (on that System Panel Header).  That should start the PC.

But this is dumbo really.   Chances are, you may slip and short something expensive.  So really for 2 GBP the cable is not so much to ask.

For simplicity at this stage, to test out the Motherboard only, it has just memory and CPU installed.  Other items like pluggable Graphics card, mini PCI card, M.2 disk or other disk can wait until your Motherboard testing is over.

Next connect up the power supply and also I connected the screen out and Ethernet

For me it helps to use a Modular Power supply so that there is a not a /rats nest/ of cables coming out.   You see here the modestly priced  (40 GBP) be Quiet, 400W, Pure Power 9

Of course Everything is sitting on an insulating plastic sheet on a wooden table so that there is going to be no chance of any electrical short.

Personally I recommend this Microsoft Media Keyboard with integrated touchpad.  It connects wirelessly using a single USB dongle.  Great for testing


If you don't immediately get a BIOS, or Boot screen something is wrong and you need to check your connections.

The monitor I use is a smart ASUS 2560x1440 native pel screen with multiple (HDMI, DisplayPort, VGA, DVI) inputs. It can also adjust to different resolutions.  So for me no display is unlikely to be due to Monitor issues.

Once in the BIOS, I immediately change the Power On settings to allow power on via a Keyboard press or mouse key.

THEN, after saving this, and powering off,  you can rewire the cable connectors market reset, that you initially had over the Power contacts, to the Reset contacts.  In future you will start the PC just by pressing a button on the keyboard, and that push button is now a genuine reset button only.

Last step is to connect the Hard Disk.  And then you can try a test install from a USB key.

I'll document the way to download a free evaluation copy of Windows and do a test install via the USB key in Part 2.

Before assembling your new Motherboard into a case it is a great idea to check it works first.  You can do this with minimal components.   It is handy to have an ATX power/ reset cable.

ATX Power Cable with HDD and Power LEDS