Computer Hardware - Power Good
This episode is about the trials of working out why the computer will not turn on even though the power supply tests ok
Back in the days of building PCs, working out why the PC no longer turns on when the motherboard status LED says its ok was always a problem
I mostly saw this on the gaming PCs as the power supply is run to its limits with graphics cards requiring huge amounts of power
Assuming the problem wasn't motherboard related, it was almost always the power supply, assuming the PC was built well
Normally the symptoms were the power supply fan "jolts" or fully powers on, while the PC will not turn on
Testing the power supply seems to show its working ok
The ATX standard (a subject we covered in an earlier podcast) saw the introduction of motherboard power supply connections
using a 20 or 24 pin main and an extra 4 pin CPU 12v supply connector
In the main motherboard power connections is a green wire located at pin 16, this has to go live (5v) within half a second
failing this the motherboard will not power on.
The test circuit this wire represents confirms that all power rails in the power supply are stable, the motherboard expects this with in half a second
The power supply might fully work taking 2 seconds, this however is outside the specification, ergo the motherboard will not power on
Most power supply testers do not check the status of this power good cable and therefore diagnoses of the problem is missed
Pushing power supplies to the limit and cheaper quality results in a short life span
The internal test system shows how efficient the power supply is, thus avoiding damage damages to the main motherboard
We always had known working power supply on hand, connecting it outside the case confirms if it was a suspect power supply thats at faulty
was a very easy test to run
