Switch Mode PSU Fault

Thread Starter


Joined Nov 16, 2006
Hi All
I am currently trying to make repairs to a Battery Charger, basically it seems to be a typical forward convertor.
I have identified some obvious blown components and replaced them but still having some trouble getting it to work.
I started debugging using an osciloscope starting with the primary side of the Rectifier. On the DC side of the rectifier i can;t seem to get the text book waveform. I have tested teh rectifier using a multimeter to test the 4 diodes and it checks out fine, i have also replaced the rectifier. #
I have posted the waveforms i get when i place the probe on the + side of the rectifier and - side of the rectifier.
Note that i can't connect the "ground" or shield of the oscilloscope probe as it shorts out the fuse in the power supply, so the signals i am gettinga re probably with respect to the AC earth.

Would appreciate any suggestions.



Joined Jul 9, 2011
When repairing things like this it's helpful to draw/extract the schematic from the pcb layout. If you could do this and post it?

Also measuring with an oscilloscope without GND doesn't mean much, if not to see if some switching element is doing its job.

Do you have an isolated transformer to power your oscilloscope (or the charger you want to repair)?