This may seem a little long winded but I hope it helps. I had been given Canox Migmaster 250 (Millermatic 250 in red) SN KB164308 that had stopped working for the fellow before me, he had put a new whip on thinking there must have been something wrong with the trigger to no avail. He thought the wire feed was the only issue but as you’ll see the weld output was non-existent as well.
I have verified that the connectors are allowing a low resistance path (0.9ohm) back to the PC1 board at RC4-2 and RC4-11, verified that the motor would spin if voltage applied directly to the input and the scr’s appear to be healthy. I obtained the technical manual and verified that transformer secondary and board logic level voltages are healthy, 24 and 15V respectively. Oh also the input voltages from wire speed and voltage pots work per values in the technical manual.
So all in all this has me to believe that all the hardware outside the board is healthy i just need to get the board to tell it to do it’s job…
Unfortunately the tech manual i got only had the main control schematic for PN 184318 control board and my board currently installed is a 146063, I thought there might be enough similarities between the two revisions that I would be able to troubleshoot effectively but they seems to be different era’s of electronics altogether.
One of the things I found with my board was that when the trigger was pressed the 15V supply to the trigger would be dragged down to around 2.5V when the board was plugged in leading me to believe that there was a short on the board somewhere not allowing the logic levels to tell the weld output or wire feed to start, i think there may have been a ground on the gate of a fet (Q13) which is in the RC4-2 input – V TGR IN STD. In my infinite wisdom i found I could isolate the two trigger inputs so i decided I would eliminate the input to RC4-2 and see if i could get the wire feed motor to spool up. Long story short I think I must have damaged the transistor that drives the wire feed motor when I removed the metal spring clip that holds it against the heatsink because when I energized the machine and pulled the trigger the transistor went up in smoke… dumb ***. I think the body was damaged as the emitter of the PNP was blackened and the current burned out through the body to the metal spring clip then to ground? thereby shorting the motor power supply out.
The gas valve was also intermittent, when machine was powered up and trigger jumpered it would randomly pick up the solenoid now and then
So I hope that sets the stage for you, ultimately my questions are:
Do you think this machine is worth spending time and money on?
Does anyone have any schematics for PN 146063 control board as well as the parts list for board level components? (have a hard time telling what the power transistor model no is after it has burned up…)
Will any version of control board for the MM250 work in any machine as a replacement?
Do you think there is a particular version of PC1 that is better than another?
The machine seems to be really clean, and certainly has not seen a whole lot of working hours in it’s life so I figured since I don’t have anything into it I would try to get it going so my son or daughter would have a mig welder to learn on. And it has a brand new whip…
Thanks in advance.