SMPS INFO & BASIC TROUBLESHOOTING ↓↓↓

Switched-Mode Power Supply (SMPS)
By Wikipedia 😊 a switched-mode power supply is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently.

Typical frequencies range from 20Khz to 2MHz.

Increased switching frequency reduces size of associated components such as the inductors, transformers, resistors and capacitors.

Generates EMI and electrical noise.

BASIC SMPS BLOCK DIAGRAM




SMPS TOPOLOGIES


Common failures and the possible root cause includes but not limited to the following:



@Point A
Compare the high voltage Vdc reading at point A using Vdc = (1.4 * Vac rms) - Vd. 
Vd is the voltage drop across rectifier diodes (0.7V Si or 0.3V Ge) but it is negligible. Thus, if the input Vac is 230Vac then Vdc = (1.4)(230) = ~322 V. If the actual reading goes much lower or higher then troubleshoot the primary side. Start with capacitors and semiconductor components.

@Point B
Now if the high voltage Vdc is good, then do check the PWM Vcc at point B. See the reading if within range compare with datasheet. If not then start tracing the Vcc line and finding the root cause.

@Point C
If the PWM Vcc is within range, then check the Vref based from the datasheet (at point C). If the reading is out, then replaced the PWM IC directly. But if got same results then replaced all secondary switching transistors and capacitors associated with the PWM.

Note: If all voltage readings were good, not only at 3 points as per above, then possibly an electrolytic capacitors goes bad. Must remove and check their capacitance and ESR. 
  OPEN   the link below to guide you checking capacitors.




Capacitor Checking