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Need help with AMT304

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  • hitnmiss
    replied
    Thanks. I will do this.

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  • jjohn76
    replied
    Can you list out what/where the tech already had you check?

    It seems like since it works when you override the contactor circuit in the electrode hot positions (VS, Stick), something may be preventing the contactor circuit from operating properly in stick and VS mode (same thing in all of the contactor on circuits? Did you try to jumper A and B in VS mode too? Does it work if you jumper A and B in all electrode hot positions (Lift Arc Tig, Scratch Start Tig)? I would first check to see if the contactor signal is dropping out when the voltage drops to 7V while you're welding (might need another person or a test jig, connecting your test leads and putting the case back on so you're out of the way of fragments if something goes).

    I would also recommend putting it in the mig position, jumpering A and B on the remote socket (should give you output power so the VS feeder works) and trying to mig that way - that should let you know if there is something wrong in the voltage feedback circuit.

    Also, measuring the voltage across pin H and pin D should let you know if the feedback circuit is working (voltage should be 1/10th the expected voltage - 0.7V at idle in lift arc; 8V at idle in Stick, VS, Scratch Start Tig; 1/10th of the mig voltage setting when you jumper A and B).

    Hope this helps.
    Jon


    ​​​​​​

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  • Bushytails
    replied
    Sorry for not replying... I've been really busy lately, and haven't had time to dig up a schematic and think about it.

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  • jjohn76
    replied
    Have you tried the lift start? I can't remember off the top of my head if that is a 7V or 15V circuit. Put it in lift start and jumper the A and B in the remote socket. Of it's 7V, something tells me your arc sensing circuit isn't working right.

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  • ryanjones2150
    replied
    Yikes.

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  • hitnmiss
    replied
    That dollar number says it all.

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  • Weld dr
    replied
    P/n 240570 $ 1470.74

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  • ryanjones2150
    replied
    Goodness....how much is a new control board?

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  • hitnmiss
    replied
    Thanks for your information and concerns about the safety issues with capacitors, I have worked with them when I worked in industrial maintenance. They are like electric fences, I learned too respect very quickly.
    I spent over a hour with a technician at Miller support, with the unit powered up we checked voltage at maybe 20 locations . He said all seem okay in main areas. He had me put a jumper wire between the A n B terminal on the 14 connector and see if it would weld okay in the CC position. It did. He said that confirmed that the problem was in the control board .

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  • Bushytails
    replied
    As I said, you also need to pay attention to safety working on these. In addition to mains voltage while you have it plugged in, the big capacitors can store a lethal charge for some time after the unit is unplugged. Any power-off testing that involves the power board or that side of the machine in general needs to be preceded by verifying with a multimeter that both capacitors are discharged to a safe voltage. And, no, don't discharge them with a screwdriver - it's bad for the capacitors, potentially bad for the IGBTs, and you'll need a new screwdriver.

    The first thing I'd check is the + and - 15V supplies. You can measure both of them on the hall effect sensor connector. The temperature of the two voltage regulator heatsinks can also point to something dragging one of them down, which causes all sorts of problems. Since you have an issue related to current control, I'd also try unplugging the hall effect sensor and seeing what changes, and measuring its output and confirming it's correct, at 0v with no weld current.

    Edit: If you haven't done so yet, you might want to run through the pre-power checklist. Since you can weld at full power, I'm not expecting it to find anything, but it's worth a check.
    Last edited by Bushytails; 09-15-2021, 07:34 PM.

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  • ryanjones2150
    replied
    I’m just a tech class (KC5HOZ), but I haven’t been active for years. My first transmitter and receiver were Heath Kits I found, brand new in the box, at a garage sale. Picked up a code practice box and a 2kw linear too, got to build them all. I loved that linear amp, two monster tubes in the middle, very positive “click” and “hum” when you turned it on. She had a warm up a minute. I’ve been thinking about getting involved again. The little I learned way back then has helped me with many things as I’ve been on my travels.

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  • hitnmiss
    replied
    Thanks for helping me with this project.
    I am not a electronic technician but have some experience with circuit boards. I held a general class Ham license (K5CMF. Assemble my gear ( transmitter) from Heath kits, you are probably too young to remember Heath kits. A few weeks ago I installed a capacitor kit in my LG tv. I believe with your expertise and guidance we could make it work.
    I have a multi meter ( Fluke) but not a scope but could borrow one.

    Leave a comment:


  • Bushytails
    replied
    tackit finally got banned? That took about a month longer than it should have. I was worried no one was going to do anything and he was going to be allowed to run the forums into the ground.

    How hot are your voltage regulators after the unit has been on a couple minutes? They're the two big heatsinks on the top board.

    Try unplugging the hall effect sensor on the positive output connector.

    The only relay is the precharge scr trigger relay, that I can think of at least. I haven't done much welder repair lately - will check the schematics when I have more time.

    Most board-level repairs will require a good multimeter, possibly an oscilloscope, a commitment to safety, and some electronics know-how. Do you have these?

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  • hitnmiss
    replied
    Thanks for your help and quick response.
    The serial number is LB186315.
    The voltage flipping occurs in both stick and VS.
    I have done a visual inspection of board with close attention to the Caps. I am using the same power source for years. I forgot to mention that when connected to the wire feeder I hear a clicking sound of maybe a relay that is sync with the flipping.
    Thanks again

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  • Weld dr
    replied
    Originally posted by Helios View Post
    Since when is this a WELDING forum? I thought it was TackIt's "copy and paste every last chain email you receive" forum!
    Lol i think Tackit got BANNED.

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