Butters AMT1800

  1. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    hi guys. Bit of advice from the electronically minded guys please.
    Bought this welder as a non runner. It trips breaker when pulling trigger. After looking through various posts I’m thinking maybe rectifier.
    This unit has 12 diodes on four heat sinks.
    One thing I noticed when having a quick nosey. When powering unit on the fan comes on fine and all seems good. I put my multimeter on the copper going into rectifier from transformer and it was reading 0.2v. Turning the power dial altered these readings marginally but not a lot.
    On the DC side of the rectifier the reading was 190mv which stayed constant varying the power setting.
    Is this the sort of output to expect when unit just turned on idle. I assumed but maybe wrong that there would be a higher voltage on the transformer wires.
    All the diodes look intact but I don’t have ability to check them. Any advice on this subject would be greatly appreciated. Thanks.
     
  2. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    Hi. Thanks for reply.
    It’s the mcb not the rcd that’s tripping.
    No trigger not pulled. As soon as the trigger is very very slightly pressed it trips.
    Borrowing a meter with diode test. Will test them then.
    Do you think I’m in the right direction with it being a rectifier fault. Thanks.
     
    tinker jim likes this.
  3. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    Thanks again for your response.
    It’s mb32 breaker on a dedicated circuit.
    A lack of wiring diagrams for this unit don’t make life easy.
    Just taken the pcb off for a look to see if anything stands out. Nothing obvious though.
    It is in poor condition though. The welder although in very good condition externally seems to have been kept somewhere damp as the board and most components inside the unit have a degree off corrosion that doesn’t match the exterior.
    The contractor is the unit which resembles a transformer on the earth line?
    I’ve got a basic understanding of electronics but these days I forget more than I take in.
    I’m trying to figure the best way to disconnect components to try and isolate the fault. Thanks.
     
  4. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    Thanks will post pics in morning. Cheers.
     
  5. Robotstar5

    Robotstar5 Casanunda Staff Member

    Messages:
    16,622
    Location:
    Birmingham
    You could disconnect (and safely isolate) the rectifier then try pulling the trigger, if the mcb holds, it's time to test the rectifier.
     
  6. eddie49 Member

    I agree with Robotstar5, the problem of the breaker tripping when pressing the trigger could be a shorted diode in the rectifier ( or a shorted smoothing capacitor, if this machine has them - large cylinders with two screw terminals connecting to heavy wires or metal strips ). You will probably have to disconnect the rectifier to check each diode, and with multiple diodes in parallel, test each one individually. Make a note of where all the connections go first.
    A diode is like a one-way valve, it will only conduct in one direction, open circuit the other way. A meter on "diode test" should show no conduction, infinity Ohms, or "OL" one way, and, by reversing the probes on the diode, the forward voltage drop across the diode ( about 0.6 to 0.7 V, or 600 to 700 millivolts ) the other way. If you have to dismantle the rectifier, make sure the insulating washers between the heatsinks go back correctly.
     
  7. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    Thanks Eddie and robotstar for that.
    I get very annoyed with myself these days. An illness has left me with problems remembering things and skills I’ve got. Little snippets I get off here just help to keep me sane with things like this and help jog my mind into the right track with things.
    Pdg who has also been very patient and helpful in his replies asked for some pics. I’m posting them soon.
    A sincere thanks to all on here.
     
    Robotstar5 likes this.
  8. bigfellayork

    bigfellayork Member

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    221
    Location:
    York UK
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  9. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    Circuit board was removed for closer inspection. It’s not in the best of condition. It’s suffering exposed tracks underneath which I will clean and lacquer. None of components appear damage just a degree of damage due to oxidising.
     
  10. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    Yes done that. Still trips but see next photo post. As I’ve taken torch handle apart. Thanks.
     
  11. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
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  12. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    Taken torch apart at connector end. Found this blue wire loose inside. Not sure if it’s been touching the crimp on the cable or anything else metallic. Before I go any further can you suggest what it is for does it need reconnecting anywhere or just a spare that needs properly terminating. Thanks.
     
  13. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    Thanks.
    Will try the torch test you mentioned then it’s out of the loop.
    As mentioned still tripped with rectifier disconnected at transformer side.
    Power and feed are all set at minimum when trying these things.
    ive Had a good look at the board and can see no shorts due to debris or corrosion.
     
  14. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    That was my next consideration cutting out the pcb.
    I think your right about the transistor on the heat sink acting as the equivalent to the contactor. Following the tracks by eye on underside it’s running direct from power in on board.
     
  15. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    I know. I’m hoping it’s a cheap fix. It’s for a young lad that’s a friend of my sons. He’s a genuinely decent lad. The sort you go the extra mile for.
    I get sick of people just writing everything off these days and also people who will only do things if it’s for their own gain.
    I’m enjoying the challenge it’s got the neurons firing. Which for me is a good thing.
    Again I must give thanks to yourself and all that has contributed so far to this post.
    It’s heartwarming to not be inundated with “bin it” “buy another” etc.
     
  16. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    Update on state of play so far.
    Disconnected wires from PCB and supplied power direct as suggested. System turned on and appeared fine. No way to check trigger on torch as wires were off pcb. No tripping though.
    While in this state switched through power settings and no tripping.
    Popped meter on wires running to rectifier while in this mode out of curiosity.
    At first it was showing various voltage changes from 2-3.5 volts not always ascending in relation to switch setting then dropped back to .2 volts through all settings.
    Transformer cool. Some heat build up in rear of power level switch where transformer is wired in.
    On the pcb the component in the large heat sink is a triac which from look of tracks runs to small transformer on the board via a couple of resistors.
    Board power is 235v at input side of transformer on pcb coming down to 16v at other side.
    The triac is performing some kind of switching between the main wire inputs on the board. L1, N and N1
    Taken all tie wraps off to follow wiring layout and check for and broken wires or shorts.
    Nothing apparent but it’s unusual to see choc block used joining different coloured wires together.
    Getting little concerned it has been messed with and not wired up right.
    On PCB input wires are;
    L1 = white running to transformer top right hand side.
    Black running to barrel connector then to white wire running to over heat lamp on front of unit.
    N = blue running up to mains switch on front of unit
    Second blue running to fan at rear of unit.
    N1 = grey running to gas valve at rear.
    Brown running to power level switch.
    There is one transistor on the board (BDV 64B) turned flat on the board. No heat sink though.
     
  17. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
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  18. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    The readings were at the transformer side of the rectifier AC side. With them still fastened to rectifier meter set on AC.
     
  19. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
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  20. bigfellayork

    bigfellayork Member

    Messages:
    221
    Location:
    York UK
    I thought this but then wondered if the unit is in a standby state when power on and transformer only fully powers up when trigger is pressed. I’m assuming this is a possibility with the triac on the pcb.
    I was thinking about disconnecting the wires from the power level switch and supplying power direct to transformer then so the level switch is out of the equation. Just not sure which pairs will supply power to transformer.
    I’m assuming from looking that the main transformer has its windings tapped into at different intervals and these feed to power level switch which then uses part or all of the windings to vary the power level that the transformer out puts.
    Sadly there are no idicative markings on the body of the power level switch.
     
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