Re: What maybe causing this Chopper to short ?
One thing can be that the U3845 (as shown in page 9) DR+ has the output stuck HI instead of turning those two Optos on and off.
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What maybe causing this Chopper to short ?
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Re: What maybe causing this Chopper to short ?
That very good manual most of them are not very good
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Re: What maybe causing this Chopper to short ?
Originally posted by selldoor View Postperhaps pictures of the board would help , take it you have ~220vac mains.
Perhaps use the dim lamp trick - a 75watt filament bulb in line wth the + mains
saves blowing up components
You can take a look at the PDF service manual , it contains schematic and picture of the PCB .
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Re: What maybe causing this Chopper to short ?
perhaps pictures of the board would help , take it you have ~220vac mains.
Perhaps use the dim lamp trick - a 75watt filament bulb in line wth the + mains
saves blowing up components
Leave a comment:
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What maybe causing this Chopper to short ?
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 :Attached FilesLast edited by SM-Piyes90; 02-25-2014, 08:56 AM.Tags: None
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