Check if the is operating system. (F1, Del, F10, ESC, F6, F12)
Check if the CPU fan is connected properly or not and is running fast and smoothly or not.
Check the output voltage of SMPS using multimeter.
See if the hard disk reinstall the operating system and check if the system restart frequently or not.
SMPS (Switch Mode Power Supply)
Switch mode power supply is used to switch the alternating current (AC) voltage into direct current (DC) voltage which is required for our computer system to work. It is placed inside the casing of the computer and from it connections are given to all parts of computer including motherboard, hard drive, CD/ DVD drive, processor etc.
Block diagram of SMPS
Orange – 3.3 V – 29 A
Yellow – +12 V – 20 A
Blue – -12V – 0.8 A
Red – +15 V – 2.5 A
White – -5 V – 0.5 A
Purple – +5 V – 2 A (Stand by (SB))
Black – Common
Green – PS on
Grey – +5 V – PG (Power Good)
Power Good (PG)
It checks all the output voltage of the SMPS and examines whether it works property or not within 0.1 – 0.5 seconds.
The power good signal prevents a computer from attempting to operate on imporper voltage and damage itself.