PC Power supply Voltage regulation limits (Min-Max) PSU inspection & Diagnosis

[Kiriakos GR]

Bellow there is a chart this demonstrating PC Power supply DC Voltage regulation limits.

In the past ten years thousands out there was wondering of why them to invest at getting a REAL in quality multimeter.
Now is the time of them to find the why... Voltage regulation limits they are consisting due high precision measurements.

This 5% Min or Max this should be the variation of the voltage alone, by taking out of this calculation the error in accuracy of the device which this is in use at taking the measurement.
Another consideration here this is the speed of measurements per second.
Even the best handheld DMM this will be able to measure voltage sag by a rate of five to seven times per second that is 5~7 delivered measurements per second.

An much faster DMM sampling  rate ( measure -> store the reading -> measure again and store the reading) this is possible only with faster and best in quality of benchtop multimeter and this would be approximately 20 times per second at 6 1/2 resolution (we can record 20 measurements within 1000ms of time).

PC Power supply Voltage regulation monitoring this is a task of high difficulty, if this it must be made properly.
Even so one quality handheld multimeter, this is very capable to measure DC voltage and give as one idea if the circuit under test this has a permanent issue in one of the DC rails at Idle state.

For testing of DC power supply under load, the solution of benchtop DMM at t 6 1/2 resolution this performing data logging, this is unavoidable if you seek reliable test results.

The use of Oscilloscope for this verification it can help in case that you are validating the quality of the power supply regarding electrical specifications compliance.

In summary:
a) Quality handheld DMM = detection of permanent damage
b) Quality benchtop DMM and data logging = verification of Voltage regulation limits
c) Quality Oscilloscope and data logging = total verification of electrical specifications compliance 
 
Such DC power supply with out any electrolytic capacitors in it output, this will deliver plain high frequency pulses which only one Oscilloscope can detect and measure. 
In conclusion 
If you are serious at PC power supply testing and or repair,  you need to have the all three measuring solutions ( Handheld & Bench-top DMM among with one Oscilloscope).   


 

 

[Kiriakos GR]

Thanks to Taiwanese brand Thermaltake  here is a chart relative to protection and when this engages.
Over Voltage
Over Current
Over Power

I am 100% confident that those specifications are given by the electronic engineers of CWT  (in Taiwan) the source which leading at PSU development when China this always running behind to catch up and never does it right.   

[Kiriakos GR]

All right, after necessary theory it is now time of me to demonstrate the best approach about the first cycle of PSU testing.

This task is possible only if we build our own testing harness.
 
We are going to need the ATX male connector, this can be de-soldered from a dead motherboard.
Next item that we are going to need this is wires, we can get them also for free, if we use the harness of a 650W dead PSU or larger in watts, we need the wire thickness to be the largest.
Quality banana plugs this is the third item.
Other parts:
a) power switch
b) small plastic box
c) small self powered voltmeter

Testing harness and servicing tasks.

Primarily the PSU testing starts as soon the PSU this gets connected to Mains (power switch on) .
Even one half working PSU this it will immediately deliver 5VSB at the purple wire,  the self powered voltmeter will measure this right away.

If 5VSB this is present?  then the next step this is PSU activation command, this is given by a short of green wire with any of the black wires.

When this mechanical PSU activation is On,  the PSU gets in to diagnostic mode, in case of no issues, this will start delivering voltage at all rails.
Additionally the PSU will produce a signal this named as POWER GOOD this supplied at the motherboard due the gray wire.

Such a testing harness it can be used only with all four multimeter connected to it, such a configuration it will increase safety and nothing will be sorted as active rail, and no electricity will came in touch with us.

Now we are able to verify entire number of voltage rails and their specific voltages. 
Next level for a more advanced diagnosis, this is us to be able to perform load testing.

Voltage rails of importance they should be tested at a minimum of 8~10 Amperes.
At my harness, when a single rail this has installed three wires, this translates that this banana plug can be connected for load testing too, the voltage measurement this is just the beginning. 
   
Load testing this is also a task for dedicated tools,  but the closest replacement this could be 40W car bulbs just as quick verification that all rails they do deliver a minimum of power under load.     
High quality load testing, the one which will deliver highest confidence, this can be performed with four units of dedicated adjustable electronic DC load.   
I have just one in my lab.

Either way, about us finding or discovering if the PSU this is within factory electrical specifications, we are going to need ripple measurements.
This task requiring a more capable voltmeter that what is offered at the handheld multimeter.
We are up to explore ACV component over DCV Rail, at a bandwidth of 40 kHz ~150 kHz,  very few special made benchtop multimeter they are capable for such a measurement.

For now just review the pictures of my own harness and get inspired.