I have been reading about the China ACDC machines around here and decided to pick one up that was non-functioning. When in MMA (stick) mode the unit turns on, the amp pot works and the digital display adjusts from 1 - 153 amps. The internal fans are on.
The OC (over-current) light is also on and the + and - weld terminals read 0 volts. It seems like there is a short causing the OC LED to come on. I pulled the cover and the left side PCB (viewed facing the front of the machine) has the green LED on and the red LED on going to the OC LED on the front panel.
I diconnected the large steel lead going to the right side of the machine and ohmed the two steel leads on that side. It read infinite so no short on the right side PCBS/alum_block. The left side with the transformers/coils reads almost zero ohms but I think it is because of the input tramsformers in parallel with the switching MOSFETS. The lower PCB MOSFETS on that side read almost zero ohms across the drain and source.
None of the MOSFETS look blown and nothing has a burned smell to it. The machine just stopped working and the previous weld bead was only 1 inch long at 80 amps.
Anyone have a schematic for this thing or have seen this problem? I am going to start disassebling the left side (PCB with green and red LEDs) and check the PCB at the bottom of the machine with two big clear cased relays (24vdc).
For those that dislike the far east machines......yeah I know.......I should throw it away. I like messing with these things. The USA units hardly ever break so they are no fun to play with.
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