help with a 300sm powcon

admin

so i recieved a 300 sm powcon from a buddy of mine and when i plug it in the dig read-out sits at around 500 for a while and then drops to -03 aprox and sits there. turning the power knob has no affect on it . but if i change the coarse knob it  will change the "clicking" feq. while the read-out is still rerading in the 500 area and if i switch the toggle (amps/volts) it wil change and then go right back . when i try to weld with it it sparks lightly but that is it not enough power to weld at all so i am at a loss im asuming the -03 is some sort of code but i cant find any info on it and hepl is greatly apreciated