pc boot problems

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Alan11985

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Jul 15, 2016
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When my computer is turned off at plug or just shutdown and I then boot it up it doesn't boot properly and the cpu light on the motherboard lights up but nothing happens but if I then unplug it and turn it back on instantly it boots fine and then will run fine with no problems. Any Ideas whats wrong.

spec
i7 7700k
asus z270i
 
Solution
RetiredChief
Could be a time out with the "I'm OK" signal. With the Power on after Power off the returned signal may be faster as some capacitors are still charged.
Quote
The ATX specification requires that the power-good signal ("PWR_OK") go high no sooner than 100 ms after the power rails have stabilized, and remain high for 16 ms after loss of AC power, and fall (to less than 0.4 V) at least 1 ms before the power rails fall out of specification (to 95% of their nominal value).

Cheaper and/or lower quality power supplies do not follow the ATX specification of a separate monitoring circuit; they instead wire the power good output to one of the 5 V lines. This means the processor will never reset given bad power unless the 5 V line drops low...
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RetiredChief

RetiredChief

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Feb 22, 2007
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Could be a time out with the "I'm OK" signal. With the Power on after Power off the returned signal may be faster as some capacitors are still charged.
Quote
The ATX specification requires that the power-good signal ("PWR_OK") go high no sooner than 100 ms after the power rails have stabilized, and remain high for 16 ms after loss of AC power, and fall (to less than 0.4 V) at least 1 ms before the power rails fall out of specification (to 95% of their nominal value).

Cheaper and/or lower quality power supplies do not follow the ATX specification of a separate monitoring circuit; they instead wire the power good output to one of the 5 V lines. This means the processor will never reset given bad power unless the 5 V line drops low enough to turn off the trigger, which could be too low for proper operation.
End quote
 
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