Why an Oscilloscope?
An oscilloscope measures and displays voltage levels in real time. To understand what this means, let's start by plotting a simple chart.
In this chart, we are looking at a time line of 12 seconds. The voltage level is represented by the green line, which can move up to 15 volts positive, and go down to -15 volts negative. For the first second, the voltage is 0, then, during the next second, it rises to 10 volts, which it holds for another second. It then drops back to 0 volts, which it holds for one more second. This action is shown in the gray area.
In the next second, the voltage drops to -10 volts, and holds that level for one second, before returning to 0 again (the blue area).
What happens next is that the voltage spikes all the way up to 15 volts for just a fraction of a second, then drops to 0 and stays there for the rest of the time.
An oscilloscope has the same type of representation. When connected to an electronic circuit, such as a power supply, it will display the voltage level (usually with a green line across a black screen), and trace out any changes in the voltage level in exactly the same way. The only difference is that instead of a time line representing seconds, the oscilloscope can display voltage changes happening in hundredths, thousandths, and even millionths of a second.
How does this help the PC technician?
The technician should already know that the PC power supply provides three critical voltages: 3.3 volts, 5 volts, and 12 volts, for the motherboard and other hardware. These voltages cannot stray very far at all without causing problems in the computer. A tech can use a DC voltmeter to read each voltage. PCI cards are also available that can display the voltages, or the tech can view them in the BIOS, or by using various programs as well, providing the computer will boot at all.
The problem with all these methods of monitoring the voltages is that numerical readouts are slow to respond. They can track the sort of voltage changes in the shaded areas in the above example, but they will not accurately show the huge spike shown toward the end. Neither will an LED display, as found on most inexpensive power supply testers. Yet, if one of the PC power supply voltages does spike like that, even for a thousandth of a second, it's enough to shut down the computer, and may even damage some of the components. The voltages must be stable at all times, with no exception.
The GT4 ATX Power Supply Tester comes with a jack that connects to the sound card of a computer. With a program like Paul Kellet's Oscilloscope (provided with the GT4), the PC becomes an oscilloscope that can display the graphical readout that will easily show such spikes in the operation of the power supply under test. No other form of tester can detect and display these spikes.
Spikes and Other Events:
What causes spikes? There are a number of reasons these spikes may occur, such as a bad solder joint in the power supply, or a component in the supply beginning to fail. It isn't important to know why it is happening, but rather that it's plain to see, the power supply is faulty, and needs to be replaced.
Another type of problem is called "excessive ripple." This is a bit more complicated to explain. Without getting too technical, suffice it to say a power supply converts AC (alternating current) to DC (direct current). AC is a voltage that swings from one extreme to the other, back and forth, as shown at right:
The voltage is rising to 15 volts, and then dropping to -15 volts, over and over again. It takes two seconds for it to return to the positive 15 volts each time. A technician could see this on his meter, as this is quite slow. In a power supply, this happens several thousand times each second. A standard meter will not be able to track the changes that rapidly.
Some of the components in the power supply are designed to stop the voltage from swinging below zero (creating only a positive voltage), so the voltage swings between 0 and +15 volts over and over again.
It's one spike after another, as seen at left. As stated before, this happens thousands of times a second, so instead of the time line being 12 seconds, let's make it a thousand times faster, or 12 milliseconds. The technician's DC meter can't read this, but will give a false, sort of averaged reading of around 11 or 12 volts.
Another set of components, including "capacitors," are designed to smooth this spiking out and lower the voltage for a solid DC voltage level of 12 volts. Now, the technician's meter will accurately read 12 volts.
See the problem? There are a number of components, such as capacitors, that can fail, without changing the reading on a DC voltmeter. This can happen with the 12 volt supply, as shown here, or with the 3.3 and 5 volt lines, and the -12 volt line as well.
These components need not completely fail, either. If the failure is just beginning, and the spiking doesn't drop or raise the voltage above acceptable ranges (tolerance), the power supply will still function properly. The spiking (ripple) will increase with any increase in the load. So a computer may work well until one tries to burn a DVD, for example, when the hard drive, the CPU, the RAM, and the DVD burner are all working at full load. This would cause "excessive ripple."
The GT4 will put this sort of heavy load on the power supply as it tests it, and allow the tech to watch the ripple change on the oscilloscope. A good power supply will show very little change, if any at all (below left), while a faulty one will show a larger change with the heavier loads (below right). The larger ripple could cause a computer to freeze, reboot, or shut down.
Summary
The GT4 will expose most common failures in an ATX power supply when used by itself. Most power supply failures are related directly to the voltage levels and how different loads affect them. The oscilloscope function provides an added level of testing more familiar to technicians with an electronics background, yet even the novice can learn to use the oscilloscope with a little practice. This added function will detect rarer anomalies and "failures in progress" that may not yet be affecting the PC. This sort of testing is most useful for quality control when building systems, verifying a power supply's factory specs, and in the rare stubborn case when all else hasn't solved the problem.
Contact Support with any questions regarding the GT4 and GWScope functions.