Troubleshooting the power supply basically means isolating the supply as the cause of problems within a system and, if necessary, replacing it.
Caution: It is rarely recommended that an inexperienced user open a power supply to make repairs because of the dangerous high voltages present. Even when unplugged, power supplies can retain dangerous voltage and must be discharged (like a monitor) before service. Such internal repairs are beyond the scope of this book and are specifically not recommended unless the technician knows what she is doing.
Many symptoms lead me to suspect that the power supply in a system is failing. This can sometimes be difficult for an inexperienced technician to see because at times little connection seems to exist between the symptom and the cause: the power supply.
For example, in many cases a parity check error message can indicate a problem with the power supply. This might seem strange because the parity check message specifically refers to memory that has failed. The connection is that the power supply powers the memory, and memory with inadequate power fails.
It takes some experience to know when this type of failure is power related and not caused by the memory. One clue is the repeatability of the problem. If the parity check message (or other problem) appears frequently and identifies the same memory location each time, I would suspect that defective memory is the problem. However, if the problem seems random, or if the memory location the error message cites as having failed seems random, I would suspect improper power as the culprit. The following is a list of PC problems that often are related to the power supply:
- Any power-on or system startup failures or lockups
- Spontaneous rebooting or intermittent lockups during normal operation
- Intermittent parity check or other memory-type errors
- Hard disk and fan simultaneously failing to spin (no +12 V)
- Overheating due to fan failure
- Small brownouts that cause the system to reset
- Electric shocks felt on the system case or connectors
- Slight static discharges that disrupt system operation
- Erratic recognition of bus-powered USB peripherals
In fact, just about any intermittent system problem can be caused by the power supply. I always suspect the supply when flaky system operation is a symptom. Of course, the following fairly obvious symptoms point right to the power supply as a possible cause:
- System that is completely dead (no fan, no cursor)
- Blown circuit breakers
If you suspect a power supply problem, some of the simple measurements and the more sophisticated tests outlined in this section can help you determine whether the power supply is at fault. Because these measurements might not detect some intermittent failures, you might have to use a spare power supply for a long-term evaluation. If the symptoms and problems disappear when a known-good spare unit is installed, you have found the source of your problem.
Following is a simple flowchart to help you zero in on common power supply–related problems:
- Check the AC power input. Make sure the cord is firmly seated in the wall socket and in the power supply socket. Try a different cord.
- Check the DC power connections. Make sure the motherboard and disk drive power connectors are firmly seated and making good contact. Check for loose screws.
- Check the DC power output. Use a digital multimeter to check for proper voltages. If it’s below spec, replace the power supply.
- Check the installed peripherals. Remove all boards and drives and retest the system. If it works, add items back in one at a time until the system fails again. The last item added before the failure returns is likely defective.
Many types of symptoms can indicate problems with the power supply. Because the power supply literally powers everything else in the system, everything from disk drive problems to memory problems to motherboard problems can often be traced back to the power supply as the root cause.
Overloaded Power Supplies
A weak or inadequate power supply can put a damper on your ideas for system expansion. Some systems are designed with beefy power supplies, as if to anticipate a great deal of system add-ons and expansion components. Most desktop or tower systems are built in this manner. Some systems have inadequate power supplies from the start, however, and can’t adequately service the power-hungry options you might want to add.
The wattage rating can sometimes be misleading. Not all 500-watt supplies are created the same. People familiar with high-end audio systems know that some watts are better than others. This is true for power supplies, too. Cheap power supplies might in fact put out the rated power, but at what temperature? Many cheap power supplies are rated at ridiculously low temperatures that will never be encountered in actual use. As the temperature goes up, the power output capability goes down, meaning that in some cases these supplies will only be capable of 50% less than their rating under normal use.
Also, what about noise and distortion? Some of the supplies are under-engineered to just barely meet their specifications, whereas others might greatly exceed their specifications. Many of the cheaper supplies provide noisy or unstable power, which can cause numerous problems with the system. Another problem with under-engineered power supplies is that they can run hot and force the system to do so as well. The repeated heating and cooling of solid-state components eventually causes a computer system to fail, and engineering principles dictate that the hotter a PC’s temperature, the shorter its life. Many people recommend replacing the original supply in a system with a heavier-duty model, which solves the problem. Because power supplies come in common form factors, finding a heavy-duty replacement for most systems is easy, as is the installation process.
Some replacement power supplies have higher-capacity cooling fans, which can minimize overheating problems—especially for hotter-running processors. If system noise is a problem, models with special fans can run more quietly than the standard models. These power supplies often use larger-diameter fans that spin more slowly, so they run more quietly but move the same amount of air as the smaller fans. There are even fanless power supplies, although these are more expensive and are generally available only in lower output ratings.
Ventilation in a system is also important. In most prebuilt systems, this is not much of a concern because most reputable manufacturers ensure that their systems have adequate ventilation to avoid overheating. If you are building or upgrading a system your own system, then the responsibility for proper cooling falls on you. In that situation it’s critical that your processor is cooled by an active heatsink and that the case include one or more cooling fans for additional ventilation. If you have free expansion slots, I recommend spacing out any expansion cards in the system to permit airflow between them. Place the hottest-running boards nearest the fan or the ventilation holes in the system. Make sure that adequate airflow exists around the hard disk drives, especially for those that spin at high rates of speed. Some hard disks can generate quite a bit of heat during operation. If the hard disks overheat, data can be lost.
Always be sure you run your computer with the case cover on, especially if you have an older, loaded system using passive heatsinks. Removing the cover in that situation can actually cause the system to overheat. With the cover off, the power supply and chassis fans no longer draw air through the system. Instead, the fans end up cooling only the supply, and the rest of the system must be cooled by simple convection. Systems that use an active heatsink on the processor aren’t as prone to this type of problem; in fact, the cooler air from outside the normally closed chassis can help them to run cooler.
In addition, be sure that any empty slot positions have the filler brackets installed. If you leave these brackets off after removing a card, the resultant hole in the case disrupts the internal airflow and can cause higher internal temperatures.
Finally, the location of the system can have an effect on cooling. I don’t recommend placing a system on a carpeted floor, as most chassis are designed to draw in air at the bottom of the front bezel, which can easily be blocked or become clogged with carpet fibers. Another problem is that a system sitting directly on a floor will ingest a large amount of dust and debris, even more so if the floor is carpeted. If you must place a system on the floor, whether it is carpeted or not I recommend elevating it at least an inch or so via some sort of platform.
If you experience intermittent problems that you suspect are related to overheating, upgraded chassis fans and/or a higher-capacity replacement power supply are usually the best cures.
- Power-Use Calculations
- Power Savings: 80 PLUS, Energy Star, Advanced Power Management
- Power Savings: Advanced Configuration And Power Interface
- Power Cycling
- Power Supply Troubleshooting: Basics, Overloading, Cooling
- Power Supply Troubleshooting: Test Equipment
- Power Supply Recommendations
- Power-Protection Systems: Surge Protectors And Line Conditioners
- Power-Protection Systems: Backup Power Options
- Real-Time Clock/Nonvolatile RAM (CMOS RAM) Batteries