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Millermatic 211 Failed Relay CR1

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  • Millermatic 211 Failed Relay CR1

    I have a Millermatic 211 Autoset that was getting power but no response to the mig trigger (no gas relay click, wire feed, or voltage across the output). It is connected to 120V when checked. The Autoset light works, and the thermal overload light will work when I open the circuit. The trigger leads have continuity from the gun connector to the control board. The fan spins slow and only has 120V across it, and the auxiliary power transformer has 13.79VAC across it. I found CR1 always closed when power is not applied to the board. The input relays (CR3 and CR5) are open and closed like they're supposed to be when power is not applied. When power is applied, the white and black leads are at the same voltage (they read 120V AC when measured against the red input lead, and ~0V AC when measured against each other). I will remove CR1 tomorrow and check again on 120V to see if I have the right voltage at the fan, and have a replacement inbound so I can reinstall and check operation. Before I do that, is there a common issue somewhere else on the board that would cause CR1 to fail?
    Thank you,
    Jon

  • #2
    I replaced the CR1 relay and all voltage levels are right when testing on 120V. The wire feed works with the trigger pull, and output voltages match the tech manual. The only problem I have right now is the gas valve stays open after the first trigger pull. It closes at power off, and stays closed at power on until I pull the gun trigger. When it stays on, I measure 120VAC across the gas valve with the trigger open, then 150VAC across the gas valve when I press the trigger. Both relays- CR2 and CR4 stay closed after that first press of the trigger (they are both open at power up). Any ideas why both relays would stay latched closed?

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    • #3
      Please post your serial number. Not sure if the manual will have the level of detailed schematics needed to figure this out, but it's worth a try; need ser no to get the correct manual.

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      • #4
        Thank you! Serial Number is LK151186N. Troubleshooting further into the circuit last night.

        The voltage across the gas valve is 0VAC on power up, then 120VAC at trigger pull and gas valve connected (144VAC when the gas valve is disconnected, and 85-105VAC depending on the output voltage setting when the gas valvle is connected), then it stays at 120VAC whem the trigger is let go (whether gas valve is connected or disconnected).
        One lead on the gas valve is connected to the red input lead through Relay CR1, which is switched on and off by Mosfet Q13, signaled by U1 through a pulldown resistor network (R58,R59). I hear relay CR1 click on at the first trigger pull, and it won't click off until power down. The Q13 Mosfet drain is 20.53VDC when the trigger is open, and ~0VDC when trigger is pulled, measured against the PCB ground. So I think the CR2 relay is getting the right signal. I replaced CR2 last night, and still having the same issues. When I test it out if circuit (33VDC across RC1-1 and RC1-6, then ground the drain on Mosfet Q13) the relay switches on and off without problems.

        The other gas valve lead splits to two places:
        It goes to the black input lead through CR4, which is switched on/by U1 through Mosfet Q16 and R70,R72 pulldown resistor network. The voltage on the Q16 drain stays at 34VDC whether the trigger is closed or not. The output pin on U1 also stays at 0V whether the trigger is pulled or not. I am guessing this relay is used in 230V operation? Should this be switched on when pulling the trigger?

        ​​​​​​It also goes to the Yellow tap on the main transformer through a R73 and C32 (resitor and capacitor in parallel). This seems to be what powers the gas valves in 120V operation? Is this right?

        I talked with Miller Tech, who really couldn't provide me much direction with my original issue (fan spins too slow, welder not responsive to input), but will try again if I can't get this resolved this weekend.

        Thanks Again!
        Jon
        ​​​​​​
        Last edited by jjohn76; 11-11-2018, 10:37 AM.

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        • #5
          Did you find a schematic for the board? there isn't one in the manual.

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          • #6
            So far, I have worked out the PCB power supply and CR1,CR2 relay circuit schematics from the board. From what I can tell, I have ~38.5VDC on the high side CR2 relay signal, and Q13 that connects to ground when it receives a high signal from the microcontroller.
            ​​​​​​

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            • #7
              Nice work! I was hoping to find a schematic in the book but that seldom happens any more. You're doing what I would be doing if it was mine and I had time. I actually have two MM211s of similar vintage, but have been unable to locate a schematic. You seem to be far ahead of where I am at this point. Will read through your posts and look at your diagram later tonight or tomorrow, but you seem to be on track to figure it out. Not your first rodeo, obviously. Hoping one of the Miller techs will see this and join in -- they may have seen a similar problem before. I have to wonder if they might give out a schematic since this is now the obsolete product. Might not hurt to ask, since it's old technology now. Would save a lot of time--I have spent many hours, and on occasion days, trying to draw diagrams from boards. I also keep searching for tech manuals for my welders on ebay; now and then you will find one with the schematic.

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              • #8
                Thank you, I really don't get too much time working on these, but reference a lot of posts from Miller_Kevin, Cruizer, Duane, and ccawgc over many years. Kevin helped me with a Miller Spectrum 2050 (repaired the boost board and replaced the IGBT with a new old stock of the shelf one). I think I just figured it out- Q12 was bad, causing ~10VDC across CR2 when Q13 was open. When I pulled the trigger, it closed Q13, which was enough to switch the relay on. When I let go of the trigger, the Q12 source and Q13 drain would float to ~20VDC from ground (the left side of D17 measured ~30VDC), and the Q12 gate would show ~30VDC. I removed Q13 and confirmed everything works on 120V. I will need to replace Q13 before operating in 230V, as it controls CR1.
                ​​​​​
                For anyone needing to troubleshoot one of these welders, here is what I would do if my gas solenoid sticks open again:
                120V mode:
                Tap relay CR2 (the right one of the two blocks boxes just below the input leads, CR1 is the left one for future reference), if the solenoid closes, replace CR2. If not, check the voltage across the Solenoid (AC). If it reads 0VAC, then the solenoid is likely the issue. If it reads ~120VAC, power down the machine. After powering down and disconnecting from power,
                check both gas solenoid leads for continuity with RC5. If either are connected to RC5, CR2 is still stuck - replace CR2. If neither has continuity, there is an issue on the board. Power on the machine, trigger open, check voltage across diode D17 (just below the bottom right corner of CR1). Which should read 0VDC. If it doesn't, either Q12 or Q13 is leaking current. Check the right side of capacitor C23, which should be close to 0VDC (reference against the board ground, which I use the rivet on Heatsink HS2 that is about 2" below CR1). If it isn't ~0VDC, Q12 is the likely issue. If it does, the issue is likely with Q13 or with the microcontroller. Measure the right side of Q13 (the mosfet drain**. If it is 0VDC, check the upper left lead of Q13 (the gate). If the upper left lead measures 0VDC, or anything other than ~5V, then replace Q13. If it reads 5V, then the microcontroller is triggering it on, or there is some debris on the board connecting R70 to 5VDC.
                There are probably other possible issues with the triggering circuit, but this makes the most sense to me.
                Hope this helps save someone else time and/or money...
                Jon
                Last edited by jjohn76; 11-12-2018, 11:13 AM.

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                • #9
                  Aeronca, what issues do you have with those MM211's?

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                  • #10
                    jjohn, great stuff! Glad you figured it out. Every time I run across an electronics problem like this, I think about buying a Huntron Tracker, but they are a little pricey for a retired guy who left all that troubleshooting stuff behind years ago. Been so many years since I used one I've almost forgotten how, but they sure are great, especially when you don't have a schematic. Now it's just hobby stuff, and helping people out when I can.

                    Thanks for posting that info; I'm printing it out and adding to the back of my MM211 manual. I have not had a bit of trouble with either MM211; just bought the second one as a source of parts since I plan to keep mine forever (however long forever is when you're 70 years old) :-) Found it in pretty nice shape with a good homemade cart, decent hood, almost new gloves, a very nice leather welding jacket, and a small bucket of brand new consumables for the gun as well as some consumables for my TIG torch. For $600 bucks, I took it.

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                    • #11
                      That's a good score!

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                      • #12
                        Glad it was helpful. I wanted to spend a little more time drawing out the phase control circuit for the SCRs on the primary side, and figure out what the feedback circuit for the drive motor, but couldn't get to it. That Huntron Tracker seems like a project in itself just learning how to use it, but looks like it would be very helpful. I have a couple different electronics testers, but an led flashlight, internet for data sheets, and multimeter work for most of what I do for hobby. This PCB is four layer - top and bottom signal/power leads, top middle is ground plane, bottom middle is 5V plane. If I shine the LED flashlight from the bottom and look at the top in a dim room, I can see all the component leads connected to ground (PCB diffuses the shadow from the bottom signal leads and 5V plane). If I shine the LED flashlight from the top and look at the bottom, I can see all if the leads connected to 5V plane. For the signal wires, I just light up whatever side of the PCB I am looking at, and use the multimeter to confirm continuity. This is my first multilayer PCB, so I thought I would share in case someone else was in my same situation. Thank you again for responding, hopefully you never need to troubleshoot, but if so, that this helps you get further a little faster.
                        Last edited by jjohn76; 11-12-2018, 12:53 PM.

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