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  • Noel
    replied
    My kid called late yesterday afternoon, a daughter, single mom...her truck won't start. My son, having called not 5 minutes before, needs a ride to pick up his kid from day care. No winter tires on the car and the drive way to steep to get traction.
    One to the west, other to the east, stuck in the middle is me.

    Learning as you get older is harder for a reason?

    I don't want you gentleman to think your efforts are in vain? They're not. I'm learning things (I'm sure others as well) , gleaning a much needed understanding of operation and function, and I'm getting it a bit where it's starting to make some sense.

    Thanks again to you both with your explanations. Understandable, adaptable knowledge. I'm sure those following along are thinking heavily as well.

    Stinson108's MM135 issue. I referenced my problems around a HH135. What I need to do is now is bring it to the wiring diagram, peel back the covers of the machine, identify and more clearly recognize components, and make sense of the path currents takes. I have both machines and manuals. I need to find the time.

    I don't mind doing the homework. This MOSFET, IGBT, capacitors, diodes, resisters and board circuits, interesting stuff. I might yet own a Dynasty? While I'm trying hard to simplify the complex, I'm also grasping how the component, it's rating as called for in operational function plays into things. Being a visual learner, I need to see my own picture, and tell myself the story to go with it.

    I remind myself slowly forward is still a forward progression.

    Thanks again!







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  • jjohn76
    replied
    Glad this helped. My S22-12P has a different problem altogether, which is related to the Mosfet driven by the jog button.
    Noel, a Google search for PWM motor control helped me understand the wire feed. Basically, the Mosfet is just a switch that turns on and off power to the motor. Because there is a capacitor across the motor leads (and the motor is inductive) the motor and capacitor create a low pass filter, which smooths out all of the fast on/off transitions from the switching MOSFET to just a steady average voltage (and motor speed, so long as the motor doesn't experience any change in resistance). The average voltage is equal to the max voltage from the power supply times the percentage of MOSFET on time (this is duty cycle). The problem is the variability in motor resistance from kinks in the wire, bending in the liner, or whatever, that require a higher/lower duty cycle to provide an accurate/constant wire speed. This is the reason for measuring the current through the motor as well. An easy way to measure current through a circuit is to add a resistor in that circuit and, knowing the resistance value, just measuring voltage across the resistor (the shunt is this resistor). This controller measures this voltage, takes the input voltage from the wire feed speed dial (potentiometer that varies voltage output based on position of the dial) and uses an algorithm to figure out the correct duty cycle, then signals to the Mosfet when to turn on and off. Microcontrollers have algorithms in written programs coded to memory, whereas the specific motor controllers use onboard comparators/etc and a bunch of resistors and capacitors connected to them for the algorithms. This explanation left out some of the components unique to the welder that isolate/protect the controller or provide more oomph to the controller to properly switch the Mosfet on and off. Hopefully that made sense...
    Last edited by jjohn76; 02-19-2019, 06:46 PM.

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  • Noel
    replied
    Thank you both. Really and truly, I appreciate your efforts and explanations.
    That's a lot to know, absorb, and it's going to take me some time to comprehend it as my brain struggles to learn more. Honestly, I'm going to need some time to digest this because it's over whelming and over my head. But to my benefit, and that of others, you both have watered the seed allowing it to grow, can't thank you enough, but thanks again.



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  • Aeronca41
    replied
    Originally posted by jjohn76 View Post
    The only thing I can add is my frame of reference when troubleshooting a MM 211 Autoset and working through an S-22P12 wire feeder that I received for an understandably good price (it would only feed at full speed, regardless of the trigger pull). Hopefully the next eplanation doesn't confuse too much but follows aeronica's block chart with what I saw on the two machines' PCBs. Pretty much the way those two feeders worked is a single MOSFET (big three legged chip on the heatsink in the upper left PCB of the MM211, on the right in the S22) PWM motor driver with current feedback. The negative lead of the motor connects in series with a shunt (two white cement resistors in the upper left corner of the MM211 PCB, one resistor in the lower right of S-22 PCB), to ground. The positive lead connects to the mosfet (I think it is the center leg of the Mosfet), with the mosfet gate lead connected to controller (network or transistors, capacitors, and resistors between), the other Mosfet lead connects to whatever the positive voltage rail is (there is a big electrolytic capacitor connected between here and ground to help keep the motor running at the right speed). The controller chip senses the voltage across the shunt, which it compares to the reference voltage from the wire feed dial (through a buffer and filter networks of operational amplifiers, resistors, and capacitors to protect the controller as well as provide the right compensation to keep the controller's time response as fast as safely possible) and determines how long to turn on the MOSFET for each pulse. The MM211 uses a microcontroller for the control chip, the S22 uses a specific chip designed for motor control. The only reason for mentioning this is because that network of transistors, capacitors, and resistors between the dial and controller and MOSFET is very different between the two. There is also a protection diode (two legged component, may be on a heatsink) across the Mosfet leads the protects the Mosfet from voltage spikes when it turns off the motor.
    Good stuff, jjohn. Takes it to the next step from my conceptual diagram, and is a great illustration of how you can do the same thing in different ways. The MOSFET drive system you describe is pretty much what I expected for an implementation method. I have an old S22P12 also that I can run with my Trailblazer, and it's nice to have someone already in there describe how it works without figuring it out completely from scratch. So far I haven't cared because I don't use it much, and it works fine, but if it ever breaks, you've already "broken the ice" in the troubleshooting process.
    Last edited by Aeronca41; 02-19-2019, 04:06 PM.

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  • jjohn76
    replied
    One thing I forgot to ask, did the gas solenoid open when you pull the trigger?

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  • jjohn76
    replied
    The only thing I can add is my frame of reference when troubleshooting a MM 211 Autoset and working through an S-22P12 wire feeder that I received for an understandably good price (it would only feed at full speed, regardless of the trigger pull). Hopefully the next eplanation doesn't confuse too much but follows aeronica's block chart with what I saw on the two machines' PCBs. Pretty much the way those two feeders worked is a single MOSFET (big three legged chip on the heatsink in the upper left PCB of the MM211, on the right in the S22) PWM motor driver with current feedback. The negative lead of the motor connects in series with a shunt (two white cement resistors in the upper left corner of the MM211 PCB, one resistor in the lower right of S-22 PCB), to ground. The positive lead connects to the mosfet (I think it is the center leg of the Mosfet), with the mosfet gate lead connected to controller (network or transistors, capacitors, and resistors between), the other Mosfet lead connects to whatever the positive voltage rail is (there is a big electrolytic capacitor connected between here and ground to help keep the motor running at the right speed). The controller chip senses the voltage across the shunt, which it compares to the reference voltage from the wire feed dial (through a buffer and filter networks of operational amplifiers, resistors, and capacitors to protect the controller as well as provide the right compensation to keep the controller's time response as fast as safely possible) and determines how long to turn on the MOSFET for each pulse. The MM211 uses a microcontroller for the control chip, the S22 uses a specific chip designed for motor control. The only reason for mentioning this is because that network of transistors, capacitors, and resistors between the dial and controller and MOSFET is very different between the two. There is also a protection diode (two legged component, may be on a heatsink) across the Mosfet leads the protects the Mosfet from voltage spikes when it turns off the motor.

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  • Aeronca41
    replied
    Noel, The conceptual drawing below might help understanding--I can't say this is how Miller did it or not since their drawings are proprietary, but the concept has to work something like this. Once you have set the wire speed control, when you pull the trigger on the gun, the motor drive circuits turn on and start the motor. (The motor and it's drive circuits may work on either AC or DC--you can design either). Motor RPM is sensed and fed back to the comparator as a voltage (or frequency) directly proportional to motor speed; where it is checked against the desired RPM which is determined by the wire speed setting. The comparator will tell the control circuit to deliver more or less drive power as required to achieve a balance between the two comparator inputs. Now, if you crank down the pressure on the drive rolls (or hold them back with a gloved hand, for that matter), RPM will drop because of the increased load and the comparator will call for more power, so the driver circuits begin to work harder -- and run hotter, reducing their life expectancy. Thus, the experience of welder techs that you see far more bad circuit cards than you do motors. The motor is apparently the more robust part of the design, and the weakest fails first.
    Last edited by Aeronca41; 02-19-2019, 08:48 AM.

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  • Noel
    replied
    Originally posted by Aeronca41 View Post
    1997CST's statement makes a lot of sense. When you crank down the pressure, it makes the motor have to work harder to turn the rollers. The motor can hack it, apparently, but the amplifiers are not designed to continually deliver that much extra drive current, and get hot. Heat is the enemy of virtually everything electronic; in the stint I spent as a Reliability Engineer, we were always about cooling things better. Keep most parts cool enough, and they will last almost forever. Get 'em hot, and they don't like it. Current above design parameters = increased heat = decreased life. I have (thankfully!) forgotten the formulas many years ago, which is probably just as well.

    There we go, a magic word, amplifiers. I do get some of this, just not much. I know enough that some where in the DC side of things the signal is weakening? Gates not opening and closing or something isn't amplified as high or long maybe?

    Cranking down on the drive rolls is like starting a cars engine with thick cold oil. So what's happening, and why? Battery not producing cranking amperage?

    I added the pictures for effect, nothing more. They could mean something or nothing at all?
    In my mind, I see a picture to explain it, I'm not sure if I'm understanding it however? I over came drive roll resistance and it was back working, but I know something is off on the snap crackle crispness. For give the simplicity, but it appears to me, the spring hold the gates closed are weakening?

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  • jjohn76
    replied
    Also, if you're looking for a cheaper alternative than buying a new board, there is a company called Innovat Corporation in Virginia that can repair your board for about $140 plus shipping based on their price listing. I am sure there are other companies that do this too, but I found this company when reading through an old thread on either here or welding web. They're sending me a replacement board for my XMT, which would have been way more trouble than it was worth to me to fix myself.

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  • jjohn76
    replied
    Stinson, if I understand your message right, you are getting voltage (15 VDC) to the motor leads when you pull the trigger? Is this when the motor is still connected? Also, where are you checking the voltage?

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  • Aeronca41
    replied
    1997CST's statement makes a lot of sense. When you crank down the pressure, it makes the motor have to work harder to turn the rollers. The motor can hack it, apparently, but the amplifiers are not designed to continually deliver that much extra drive current, and get hot. Heat is the enemy of virtually everything electronic; in the stint I spent as a Reliability Engineer, we were always about cooling things better. Keep most parts cool enough, and they will last almost forever. Get 'em hot, and they don't like it. Current above design parameters = increased heat = decreased life. I have (thankfully!) forgotten the formulas many years ago, which is probably just as well.

    Leave a comment:


  • Noel
    replied
    When I started in this racket, they were still gas welding air craft fuselages. The home built crowd still does, or at least those that haven't been sold on GTAW as being god's gift to welding everything. I have plans for a 3/4 scale SE5A bi plane. Just saying, you guys who fly...we on the ground hold some envy to you. Not enough life probably but I have the plans.

    Stinson 108, I'm not the gifted one on fixing welders. I gave up what worked for me, and admittedly still have questions that have no answers that I fully understand.

    Now this board failure stuff. My ol man would say, leave the thinking for the horses, they got bigger heads. Well it's easy to say, replace the board. That's the world we live in. The TV...Oven doesn't work, Dish washer, Microwave, Laundry machine, Fridge...welder?

    What I want is something more then that for explanation. What I'm finding is the information that's out there, while available, you have to dig for it to find it, need and have a willingness to learn and digest it, and it comes in small pieces that then have to be applied to understand how it works and is applied to operate and function.

    I didn't loose welding characteristics, I lost low end speed control and drive motor torque.

    Maybe I didn't diagnosis it well? But it worked for me. Would replacing a board put a crispness back in it's step? Maybe? But because I didn't go that route I discovered a degree of resistance in the drive. Hmm?
    I have a buddy who repairs watches and clocks...friction keeps poor time.

    With that working again, it lead me to thinking I have something else electronic on the way out? That something is weakening in function and the only way to know for sure is to understand how it functions and plays a role in making things work?

    What I'm slowly learning is how electronic switching devices work and function. How electronic filters work, resisters, capacitors...all those things on a wiring diagram. How to test them. And then the board to is understandable.
    Not high on my list really, but I retain stuff. Small scraps of paper, the pile is building up.


    -1997CST Board failure is mostly cause by drive rollers cranked down too tight on these small machines. I've seen 1 motor failure to 100 board failures. "

    I have to ask, please tell how that cranked down pressure causes that to occur? And if you have seen 100 board failures, is that where it stopped? I'm thinking your holding out the orange but not giving it a hard enough squeeze?







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  • stinson108
    replied
    Noel... the serial number is LC489437 .
    1997CST... I checked the wires and I'm getting 15 volts . I'm assumming that's alright . I connected a 9 volt battery on the drive motor and it turned the motor over .

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  • Aeronca41
    replied
    Looks like there are at least 2 different part numbers for that board. You'll have to check your machine's serial number, get the proper manual from the SUPPORT link above if you don't already have one, find the part number of the board, and then call Miller for an updated part number since the ones in the manual are no longer available. Looks like 207463 or 207466 in a random serial number manual I looked at. 207466 has been replaced by 226321; not sure about the other one. Looks like $250-$300 bucks or so. Talk with Miller at 920-734-9821. Check at Miller4less.com for pricing once you get a good part number. Miller does not provide schematics to fix the board except to their authorized service folks.

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  • 1997CST
    replied
    Most likely it's the PC board. Don't take the motor apart. Get a meter, disconnect the wires to the motor and check for 12 VDC across the wires. If it isn't there it's your board. Make sure your heat setting isn't in between #'s. Board failure is mostly cause by drive rollers cranked down too tight on these small machines. I've seen 1 motor failure to 100 board failures.

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