HF 165 TIG/Stick DOA

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So, I bought a broken harbor freight TIG/Stick welder (98233 I think).  Call it for entertainment value to see if I could fix it.  Kind of stuck right now as the 220 power comes on, makes DC for the chopper board but no output.  Chopper IGBTs all test OK.  Chopper driver board components test OK.  Backing up to the controller board I am not finding the problem obvious as the 18 volt supply is up and running but I can not detect any output to the chopper driver board.  Should be a small high frequency signal to turn on the chopper driver transistors.  Nothing.  Looking for bad solder joints but that seems unlikely.  Anyone have a dead one or something in the 2010 era with A P06060506-4 controller board that I can buy?  A schematic would be a great help also.  Can't find anything as usual.  The "Chinese Welder Forum" disappeared from yahoo and their remnants are pretty skimpy.  UTube is some help.
Reply:Had that on a miller suitcase inverter mig. Bad optocoupler is what I ended up finding after stupidly fixing the rest of it to death. The optocoupler isolates the igbt driver from the low voltage side of the board. Just a guess hope it helps!