Hello everyone here .
Am right now trying to repair a switching style power supply , this one converts low input current to pretty much 160 amps to be mainly used as a MMA welder .
Anyways i checked it step by step , started with the primary side , the primary caps got 300 Vdc on them , now arriving to the chopper circuit witch consists of 2 power IGBTs , that are making the input signal chopped at a very high frequency with the command of a pulse width modulation chip " UC3842 " .
So i checked the power transistors with a continuity tester , and they are both shorted , also found 2 shorted A3120 optoisolators , four 18 v zeners .
I then changed them all with new parts , in the hope to save this unit but again all the parts that i' ve replaced have again fried .
I guess something else is causing them to burn , i hope i get some ideas from people who encountered similar issue .
Here is a Service manual of the SMPS welder :
Am right now trying to repair a switching style power supply , this one converts low input current to pretty much 160 amps to be mainly used as a MMA welder .
Anyways i checked it step by step , started with the primary side , the primary caps got 300 Vdc on them , now arriving to the chopper circuit witch consists of 2 power IGBTs , that are making the input signal chopped at a very high frequency with the command of a pulse width modulation chip " UC3842 " .
So i checked the power transistors with a continuity tester , and they are both shorted , also found 2 shorted A3120 optoisolators , four 18 v zeners .
I then changed them all with new parts , in the hope to save this unit but again all the parts that i' ve replaced have again fried .
I guess something else is causing them to burn , i hope i get some ideas from people who encountered similar issue .
Here is a Service manual of the SMPS welder :
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