Re: PSU how to test one
That is a really nicely produced tutorial!
But I do have a couple comments, if you don't mind. There is no mention of any ESD precautions. While I understand this tutorial is focused on testing a power supply outside the PC case, it is very likely users will be removing the PSU from the PC case, and/or disconnecting power connectors to test the PSU with the PSU still installed inside the PC case. In either event, if ESD precautions are not taken
PRIOR to sticking their hands inside the case, the user may very well destroy an ESD sensitive device, such as the CPU or RAM module without even being aware any static discharge occurred. Therefore, I recommend some warning in addition to unplugging from the wall to touch bare metal of the case interior (or use a
anti-static wrist-strap)
before reaching in to put user and computer/PSU "
at the same potential" thus ensuring no discharge can occur.
It it very rare for capacitors to hold on to charges as you describe in your warning because even budget supplies bleed that off in seconds when power is removed. HOWEVER, if there is damage, a faulty component, or poor assembly techniques uses - all bets are off so the important part of your message (Do not under any circumstances open the case on any PSU!) still certainly applies.
Sadly, there are many who feel since it is (relatively) safe to remove the side panel of a "running" PC and dig around and not risk electrocution, they feel they can do the same with a power supply that contains lethal voltages inside - perhaps to dig around inside the PSU with a multimeter! That is not recommended unless you are a formally trained electronics technician.
I note you say,
This is meant to determine if a suspect PSU is bad or not and not meant to be a definitive PSU test tutorial.
That is great. But note those methods can confirm a PSU is bad (if a voltage is missing, for example), but not necessarily that a PSU is good. And I note you also said at the bottom,
You are done! This should determine whether this PSU is good or bad.
You cannot conclusively test a PSU with a multimeter - especially using the paper clip method. To properly test any power supply (whether it be a computer PSU, battery, or car engine) the supply MUST be under a proper, realistic load - preferably tested over a wide range of "expected loads" (a requirement for
80 PLUS certification). A failing (or very cheap) PSU can measure within tolerances with no load (idle), then fail when put under a greater (but still realistic) load. So to measure a PSU properly with a multimeter, the PSU must be connected to the motherboard (realistic load) and powered up. That means jamming (with considerable force!) hardened steel, highly conductive, sharp, pointed probes into the main power connector deep in the heart of a live computer. That can take some significant physical dexterity (not to mention strategic and correct placement of your tongue) where one tiny slip can cut through several tiny circuit traces. Disciplined ESD prevention is essential! Therefore again, IMO testing with a multimeter should be left to a professional, or at least someone with this type experience.
Also, most multimeters are incapable of measuring
ripple and other anomalies that "ride" on DC voltages and affect computer stability. Your +5VDC can measure +5.00VDC but if the PSU is letting too much ripple through, freezes, system crashes, reboots and other problems can occur.
The plug-in testers are good, especially those with a digital readout, IF they go out at least 1 decimal point like this PSU Tester (not sure if the Rosewill does for the +12V - I keep a
PSU Tester in my truck tool bag). These testers typically have a little 10W resistor (well, 10W is big, for a resistor) for a small load, but not a realistic one. And none of those plug in testers measure ripple either.
Therefore, the only
conclusive way to accurately test a PSU is with a qualified technician using an oscilloscope or a power supply analyzer - sophisticated (and expensive) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results. Therefore, conclusively testing a power supply is done in properly equipped electronics repair facilities.
This is why swapping in a known good supply is often the best way to test a supply.
In my canned text for testing PSUs, I include a link to the
ATX Form Factor PSU Design Guide and reference “Table 2. DC Output Voltage Regulation” on Page 13. That way, I don't have to worry about me typing wrong information in my canned text, like your tutorial saying the 3.3VDC high-side tolerance is only 3.165 volts!
One last thing, I promise. There is nothing in the ATX PSU Design Guide, or the main
ATX Form Factor Standard that "requires" a standard wire color code scheme (except for the newest standard, SATA cables). They are only recommended color coding schemes and PSU makers do not have to comply - though most do. Still, there are some, typically older PSUs from off the wall manufacturers that did not use standard color codings. Therefore, it is always best to go by, or at least verify by pin number - which is standardized (unless modified like older Dell and HP PSUs and motherboards).
Sorry if that was more than you asked for.
