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Power Good Problem In ATX Power Supply

By Jestine Yong on June 27, 2013

I managed to fix the power supply partially and measured all the 24 pin and they all have proper voltages (3.3V, 12.1V, 5V…etc.) however one issue remains…. I’m using coolmaster ATX tester and it passes all the voltages except PG which show as ‘HH’ which means it is above 900ms and is beeping. Can you tell me what is causing that power good delay in Power Supply? Which component is responsible for it? What should I check (capacitor, resistors, diode, mosfet, power IC….?)

Answer:

PG problem can be due to bad main filter cap, secondary side PWM IC and corresponding components like open resistor, bad caps and leaky diodes. What you need to do now is to trace backward from the PG point. All components related to the PG line can be a suspect. The line will usually lead back to the PWM IC or Op-amp ic. Try replace that IC and if the problem still remain the same then the only choice is to check all the components surrounding the IC.

Don’t forget I came across few cases where one of the main filter capacitor open circuit causing the ripple to enter into secondary side disabling the PG signal.

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