TROUBLESHOOTING PCB/BOARD WITHOUT SCHEMATIC ↓↓↓

My own method in repairing confirmed faulty PCB (Printed Circuit Board) without schematic diagram and no clear failure information.

STEP-1 
LOOK FOR POWER-INCHARGE-COMPONENTS AND DO OHM-CHECK.
PCB in general has power-in-charge components, I will find this area first. 
Common components involve are: 
Fuse            Regulators        Electrolytic capacitor
Diodes         Transistors        Inductors 
Rectifier      Transformers     DC-DC converter module 
And then I will check those components for any abnormalities: fuse blown? shorted or low-ohm diode/mosfet? High ESR capacitor? 
Image below are 3 PCB samples and their power-in-charge components.



STEP-2 
POWER-UP THE PCB AND CHECK FOR UNUSUAL VOLTAGES.
If all power-in-charge components ohm check are fine then I will power-up the PCB and check for unusual voltages.

Method 1:  Look for regulators or DC-DC converters and supply enough input voltage, based from datasheet, using external DC source. Check the output of regulators or DC-DC converters for any abnormal readings. Start troubleshooting if needed. Example as below:



Method 2:  If there are no regulators or DC-DC converters, I will use the electrolytic capacitors voltage rating to estimate the voltage input to power up the PCB. Example as below.


Important: Make sure to power-up the PCB with correct polarity. If the external DC source goes on constant current mode when powered-up the PCB then there’s a shorted components. I check these components first: diode, mosfet, transistors, rectifier, shorted resistors, and other semiconductor components.


STEP-3 
Ok if step 1 to 2 are all just fine then I will use the so called “Shotgun Method”. I will start replacing ICs that are related with the failures. Because functional failing ICs are very difficult to detect using offline troubleshooting. Believe me, I did a lot of success repairs too using this method.

 OPEN  the link below to guide you in selecting IC to replace.




» Troubleshooting part without schematic