Troubleshooting a dead Maxstar 150 STL for a friend. Plug it into wall power, flip the switch, and nothing happens. Welder acts as if it has no power... front panel is completely unresponsive. This is an old model (SN LE050152M) that doesn't have an inline fuse.I get the cover off and do a visual inspection, no obvious signs of damage.I get the cover off and power it up. Mains switch is working fine. With the cover off I can hear an audible squeal which is either the switching circuit, or a dying component.Looked at the welder with the thermal camera. Only signs of life is two of three (what I believe to be) power resistors and the heat sinked IC adjacent to them getting warm... see imagesThe leftmost white box I can read the printing... says RCD K3-361 on the top line, 10W 15K on the bottom line. Sure enough, I ohm it out and it's 15.1 kohm. I check the other two, and they're not giving a solid reading... moving around like when you put an ohm meter across a capacitor. Google search on the part number turns up nothing. The three parts are jammed so close together, I can't read what values the two rearmost are supposed to be.The adjacent IC that seems to give off heat is the switching IC... PN 1M0680R... datasheet here: https://www.mouser.com/datasheet/2/3...RB-1120775.pdfThe main board has two large caps on it... values check out fine. The positive rail on one is tied to the negative on the other. The next largest cap on the board, quite a bit smaller, also checked out fine.With power on, I measured the following:Rear-most cap: 85 VDCFront-most cap: -79.5 VDC (my positive meter lead was on the negative terminal of the cap, since this is the common terminal between the two caps)Rear-most Power resistor: 72.5 VDC across the leadsMiddle Power resistor: 79.7 VDC across the leadsFront-most power resistor: -6.8 VDC across the leadsSmaller cap (shows orange in thermal image... but wasn't warm, metal face was actually reflecting my IR signature): measured 2.3 VDCI didn't have the pinout for the switcher at the time, so I didn't check VCC on it. Can't get to it right now to see if it's in spec.Anyone have any experience troubleshooting this model, or have any suggestions based on the info I've provided so far?
Reply:Thinking about this for a few minutes, I definitely need to get back in there and check VCC on the switcher and whatever else that I can safely probe.The total voltage across the caps, about 165V, makes sense. The power resistors, I have no idea what they're for, or why the two are behaving as they are. I hope someone here can give me some insight.
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id you check the board close to see if there were some fuses blown, or anything else. These aren't the obvious fuses they are soldered into the board.Arcon Workhorse 300MSPowcon 400SMTPowcon SM400 x 2Powcon SM3001968 SA200 Redface1978 SA250 DieselMiller Super 32P FeederPre 1927 American 14" High Duty LatheK&T Milwaukee 2H Horizontal MillBryan
Reply:Originally Posted by blawlessDid you check the board close to see if there were some fuses blown, or anything else. These aren't the obvious fuses they are soldered into the board.
Reply:If you have power to the pcb either 115 or 230 volts. Follow the wires from the switch.And welder does not light up. no blue light. Power pcb is dead. the whole power pcb will have to be replaced.Trying to repair is near impossible. There are no published diagrams and miller will not give any out.I would have a Miller authorized shop install the power pcb. that way you get some warranty.Self installed Miller pcbs will void any warranty on the new pcb.
Reply:Originally Posted by ccawgcIf you have power to the pcb either 115 or 230 volts. Follow the wires from the switch.And welder does not light up. no blue light. Power pcb is dead. the whole power pcb will have to be replaced.Trying to repair is near impossible. There are no published diagrams and miller will not give any out.I would have a Miller authorized shop install the power pcb. that way you get some warranty.Self installed Miller pcbs will void any warranty on the new pcb.
Reply:Odd that you can hear the switcher, unless you are hearing a harmonic.Those type power supplies are nasty to trouble shoot,too many feedback circuits.They tend to use simple ways to power switcher chips, might have a shorted zener or a shorted cap.Some of the older welders had a low power circuit as the first thing that gets power.It provided plus/minus power to the logic boards and the relays.If it went out nothing would work or light up.I suppose check the power running the switching chip (VCC) and see if a feedback circuit is messing with the chips control lines.Last edited by Bluewelders; 08-18-2018 at 03:17 PM.
Reply:Working through something similar right now. the board is real similar to my Passport Plus, I think those 3 big resistors are all the same value, there is a 0 ohm resistor used as a fuse on mine. get the magnifier out and start lookin around the middle of the board, but I think it may only protect one of the ICs. Ive learned a lot from my repair attempt so far, like my shop teacher used to say: "Dont destroy the evidence" dont start desoldering and poking too hard til youre sure youre on the right track. Youll end up buying a bunch of stuff from Mouser or Digikey that wasnt broken before. Id check all the tiny stuff first, get tech sheets for everything i can get a part number on and look for vcc and gnd on all of it. Theres multiple control voltages depending on the IC in there and way more on the switching section. Just be careful!!!
Reply:I'll buy it off ya, pm me i need to either use two to make one or redeem myself by fixing yours
