By Ira Wilner
I’ve built - or rather more correctly, assembled - my own personal computers since the dawn of personal computing with the Popular Electronics Altair computer project in the 1970s. Today, assembling a gaming or computational powerhouse is easier than ever before as compatibility between hardware components, motherboards and the operating system is far better than in the past. However, not every manufacturer gets their end right. For basic wiring stupidity I present the following:
Cooler Master the manufacturer of the gorgeous HAF 932 tower chassis designed to provide exceptional air flow for those hot-rodded, over-clocked CPUs provides the normal assortment of wiring to connect the front panel power switch, reset and hard drive activity lights along with two USB and one firewire port. Problem is. they tried to improve upon it by tying all of the circuit grounds together.
In most computer-case designs the wiring to the power and hard drive activity LEDs are isolated. They had better be! All motherboards and drive controllers that I’ve ever used control the return or ground side and provide a constant +5 volts on the hot side. With the HAF the net result is the hard drive light will remain permanently lit! And if you accidently reverse the wiring polarity at the motherboard you risk damaging the drive circuitry, perhaps burning up a current-limiting resistor.
The fix required removal of the circuit board in the top of the case, the use of an Exacto blade or sharp scribe to cut the ground plane around the cathode pin traces of the LEDs and the ground return pins of the chassis PC board cable socket and then soldering jumper wires to provide isolated negative lead connections to the LEDs.
Problem number two, also with the HAF 932 tower case. This was not only a design flaw, but a QC issue. A couple of the pins in a connector to the front panel board carrying a USB port were reversed in assembly at the factory. Normally this wouldn’t cause a problem until you actually plugged a USB device into it. But because all of the grounds were tied together on the board, the pin reversal created a USB power rail short! When I booted up the motherboard for the first time the POST firmware immediately reported a USB power overload fault condition. Fortunately, the USB power specification suggests built-in current limiting protection. Using fine tools, sewing needles, I was able to extract the errant pins and place them back into the connector in the correct order.
So, where was QC? With all the common grounding, they actually made it easier to check for wiring faults!