How to repair a power adaptor

How to repair a simple power adaptor 

Prelude:

Servicing an electronics gadget is a challenging task. Unless one knows the working principle of the particular circuit design, it is somewhat difficult to repair the gadget and bring back to its normal working condition. On the demands of many i attempt to present here a simple way of troubleshooting a defective power adaptor that normally uses as a power source for the gadgets to function. 

The gadget under repair is 'A 6V DC power adaptor'.

Normally the power adaptors are used for charging purpose or external power source to run the gadget. The power adaptor here employs single rectifier diode that converts a low voltage AC to DC for our purpose. A stepdown power transformer is used to reduce the normal 230 V AC available at the wall electrical outlet. The transformer steps down to 6 V AC which is then rectified into DC and smoothed before taking the output for the gadget to be connected. 

Circuit schematic

The circuit schematic of this adaptor is self explanatory since it is a very simple circuit design working as half wave rectification mode for simplicity and cost effective. 

PT is the step down power transformer. IN4001 is the silicon rectifier diode for conversion. C2 is the electrolytic capacitor which smooths the DC output. F2 is the glass fuse for safety of transformer and the diode. 

Go through the circuit schematic before attempting any servicing steps to be undertaken for troubleshooting and repair.  

Trouble shooting 

Test point                Voltage                  Probable defect                                Troubleshoot

1. Adaptor output    6V DC                   Working fine

                                    0 V       Some defect in power supply/component   a) check wall power supply   

                                                                                                                     b)  check power cord

2. Point 2 in SW2       0V        SW2 on/off switch  defective         Disconnect Wall supply /check switch 

3. Point 1 in PT          0V                     F2 fuse open                       Check fuse for continuity

4. Point 3 in PT          0V                230V AC at pin 1                    PT primary open- check for continuity

5. D2 Cathode           0 V                  a)   C2 short                              Check C2 for short or leakage

                                                          b) D2 diode open                      Check D2 for open

These tests are very important test points to ascertain major defects in the circuit functioning. There may be very minor defects in soldering/ loose connection etc. which can be identified and rectified easily.   

For testing voltage, continuity etc. a good multimeter may be useful and handy to easily pinpoint the defective components/connections. Hence minimum test tools are required for any servicing work apart from a good soldering iron. 

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