Shrink Way Wielder
- Jan 20, 2018
That's the problem with those PSU testers - they don't really test much, as they place zero load on the PSU. And a PSU needs to be pretty broken to not show correct voltages at zero load.No clue either...
To sum up:
- There is no problem on the 'computer' hardware parts as you are able to start the computer with an ATX PSU
- You are able to start the computer when the PDCB is connected to an external brick, so the PDCB is also fine
-> then the only remaining part that can be faulty is the PSU
- The PDCB output values when attached to the PSU give good results on the tester
-> so the PSU seems to be working as expected, at least when there is no power draw or very few
Don't you have another setup that requires less power to test your PSU with? Like a motherboard with an embedded CPU drawing 20W from the wall or something.
Or having the PSU to take care of the motherboard only, and the ATX PSU for the CPU?
If that's not risky for your hardware that is, just thinking aloud here...
Well maybe it's time to summon our 12V chief magician @Thehack !
There are cheap ways to do some simple load testing (even if it is by no means equivalent to proper PSU testing): Buy a set of powerful 12V lamps - you should be able to find up to 60W relatively easily (car headlights, for example). Connect these to the PSU, ideally in parallel to the PSU tester. As this is a pure test setup and at low voltage, there's no need for fancy wiring - just get it hooked up, ideally in a way that lets you relatively easily connect and disconnect the loads. See how the PSU reacts to scenarios such as the sudden addition of loads from zero power draw by monitoring voltages on the PSU tester. (Worth noting: incandescent lamps are purely resistive loads, while a PC is a complex combination different loads. Using pure resistive loads for PSU testing is thus not really realistic - but it can give some indication of PSU behaviour.) If the 12V voltage drops significantly, then that's your answer - which would likely be due to an insufficient bulk capacitor in the PSU (likely IMO for a compact, low output LED driver), coupled with too slow transient response (if the PSU has no voltage monitoring, which is likely the case for an LED driver, then it has no way of compensating for sudden load spikes and the accompanying voltage drops), either causing the cap to drain and the motherboard to no longer see a sufficient voltage for operation, or it might even trigger some form of protection in the PSU if the inrush current from the PC is sufficient. Either way, that would result in the PC simply not booting, as from it's point of view it's not actually receiving power.
Another highly useful tool in a scenario like this would be a clamp style multimeter/ampmeter, to measure the current draw from the PSU when turning on the PC. The filter caps on a large CPU VRM can cause quite high inrush currents when connected to power, even if nothing in the system is actually drawing significant power - the filter caps want to fill up as quickly as possible. This could be enough to trigger OCP on your PSU if it's sensitive.