Sealey Super Mig 150 Repair

  1. thomp1983 New Member

    Messages:
    13
    Location:
    newark on trent, UK
    Hi Folks,

    first post here looking for some help with my Sealey Supermig 150. I bought it second hand a couple of years ago and at the time the seller mentioned the inverter had failed so he replaced it, no problem the welder worked when he demonstrated it so I bought it, when I got it home I found the torch is always live so I put it on my list of jobs to look at later.

    Fast forward a couple of years and it's now made it to the top of that job list along with tidying up the insides of the unit.

    I don't know a huge amount about welders hence asking you guys for help with what's what, lets start with some pictures of what I've got.

    [​IMG]

    Front Of The Unit

    [​IMG]

    Rear Of The Wire Feed Switch Used To Adjust Wire Speed (I've Unbolted It From The Front)

    [​IMG]

    This Looks To Me Like Another Wire Feed Speed Unit, I Wonder If It's The Original For The Unit And Has Failed In Some Way

    [​IMG]

    Front Of The Wire Speed Feed Unit I Use To Adjust The Feed

    [​IMG]

    A Relay That Hangs Freely Inside The Welder

    [​IMG]

    I Think This Is The Coil That Activates The Wire Feed When The Torch Trigger Is Pulled

    [​IMG]

    This Is The Inverter The Previous Owner Fitted

    [​IMG]

    Don't Know What This Is But I Mention it In The Wiring Shortly

    [​IMG]

    Back Of The Mystery Unit In Picture 3

    [​IMG]

    Don't Laugh, A Very Rough Diagram Of What Wires Connect To Where, The Descriptions Are From The Parts Each Wire Connects To.

    The unit in picture 3 and the black relay both hang and swing around inside the welder, I don't like this so once I understand what they are I either need to remove them or secure and tidy there wiring up properly.

    So I need your help please to identify why the torch is always live and what needs rewiring to make it work correctly and what the unit in picture 3 and the relay are there for and if they are required or can be removed and the wiring done another way?

    Cheers
    Chris
     
  2. pedrobedro

    pedrobedro Man at Matalan

    Messages:
    10,705
    Location:
    CX Derbyshire
    I'm no expert either but it looks like someone has swapped the original wire feed motor for a 12v one and the inverter is there to supply it with power. Picture number 6 looks like a wire feed motor. Does the hanging relay click when you pull the trigger to start welding ? The don't know what it is picture looks like the diodes. Don't know about the permanent live torch it must be a wire that should be switched has been direct connected.
     
  3. eddie49 Member

    This is what the circuit diagram should look like:

    Supermig150.jpg
    The wirefeed control in your Picture 2 is a new addition. The original wirefeed control, auxiliary ( 24v ? ) power source, and on/off relay is in Picture 3. I would guess that the small transformer mounted on that PCB burnt out, and was replaced with the "inverter" - a mains-power 12v LED light driver ( Picture 7 ). The automotive-type relay in Picture 5 is, I think, the key to why the MIG torch is always live.

    Decoding where all these new wires go and what they do won't be easy... I would suggest fixing the original PCB ( Picture 3 ) and going back to standard wiring would be the best plan. Use an Ohmmeter to check the primary and secondary resistance of the transformer. If it is burnt out, they can be obtained quite readily - search eBay for "potted" or "encapsulated" transformer.
     
  4. thomp1983 New Member

    Messages:
    13
    Location:
    newark on trent, UK
    Thanks for the responses guys, Eddie what you've said sounds very much like the case for what's happened, I assume the transformer is the big square lump in the middle of pic 3?

    From reading old threads in this forum it appears the relay and white resistor in pic 3 are also known to fail so I think I'll replace the lot and reflow the rest of the joints in the board.

    Fortunately most of the wiring looks like it has been piggy backed onto the original wiring instead of cutting out and rerouting it to the new components so shouldn't be too hard to remove

    Thanks
    Chris
     
  5. eddie49 Member

    Chris, yes, the transformer is in the centre of Pic 3. The output, as marked, is 12v AC ( not 24v ). The primary resistance may be 1 or 2 K Ohms, and the secondary perhaps 200 Ohms. Note that other components in the circuit may affect these readings.
    A typical replacement for the transformer would be:
    https://www.ebay.co.uk/itm/BVEI3022...-1-5VA-230VAC-12V-125mA-Mounting/312796456247
    The pin spacing may not be an exact match for the original; short pieces of wire may be needed to link up.

    The white resistor looks OK, it is probably supposed to be less than 100 ohms.
    The relay coil should show about 100 Ohms. The contacts have a tough life, handling 1 or 2 KW to the main transformer, so check that they are clean and not fused together.
     
    Last edited: Oct 24, 2019
  6. thomp1983 New Member

    Messages:
    13
    Location:
    newark on trent, UK
    https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/312796458359

    Any reason I can't use the above as it has a higher rating than the original?

    Currently thinking to remove the wire speed pot from the board and mount the board separately on stand off posts with wires to the pot and possibly the transformer if it won't go on the original board.

    The relay also needs replacing, it failed during use yesterday but I've sourced a replacement for that.

    Cheers
    Chris
     
  7. eddie49 Member

    Chris, that transformer with a higher rating ( 3.6 VA, 300mA ) will be fine. The relay coil resistance is probably about 200 Ohms, so it's only going to take 12 / 200 = 60 mA. The small transformer only runs the relay; power for the wirefeed motor comes from the main welding voltage.
     
  8. thomp1983 New Member

    Messages:
    13
    Location:
    newark on trent, UK
    Finally had time to look at this today, both the new relay and transformer were direct fit replacements.

    With the new components fitted and the output to the wire feed motor rewired back to the original pcb everything now seems to work as it should I'll know better when I eventually set up a test piece to weld.

    Thanks for the guidance, now to have a look at the sip unit I have that doesn't work.

    Chris
     
  9. eddie49 Member

    Chris, thank you for the update, and I'm glad to hear that things are looking good.
     
  10. thomp1983 New Member

    Messages:
    13
    Location:
    newark on trent, UK
    Well it seems I'm having more issues, no doubt something i've done.



    Firstly occasionally when starting the arc you get the above sparking in the bottom of the unit, it appears to be from one of the connections to the transformer, is this normal, is it just a case of needing to clean up the connection or is there a fault?

    Secondly since I've repaired the original pcb and rewired it the wire feed pot doesn't seem to have any effect on the wire speed, you can here the motor speed change when changing between the four switches on the front but it doesn't change at all when using the pot for the wire speed, I've checked the pot on the pcb with my meter and the readings vary as the knob is turned so it appears to work, how would I start to check this I'm sure I've got the wiring right according to the diagram
     
  11. eddie49 Member

    There should not be any arcing inside a welder! The transformer secondary windings are probably aluminium ( rather than copper ), and can corrode with steel parts at bolted connections. They can also loosen because the soft metal "creeps". Check by opening each joint in turn, file clean if necessary, and tighten, then re-tighten a day later. Spring washers can help too.

    Since power comes from the welding transformer, the wirefeed motor speed does "step up" as you change power range, but it is also supposed to be fine-tuned by the pot on the PCB. Most of the small speed controllers use an SCR, or a power transistor, as the output stage. Maybe that component has gone short-circuit.
     
  12. thomp1983 New Member

    Messages:
    13
    Location:
    newark on trent, UK
    Thanks Eddie, there is a component on the board marked scr1 looks a bit like a 3 legged fet I'll see if I can get some more details off it it tomorrow and find a way of testing it

    Chris
     
  13. eddie49 Member

    An SCR ( silicon controlled rectifier, or thyristor ) has three leads, and is like a diode, in that it conducts in only one direction - anode to cathode. However, it will only do this after it has been triggered "on" by a small positive pulse or voltage on the Gate with respect to the Cathode. In the absence of a trigger signal, an SCR will not conduct in either direction.

    I think that your SCR1 has a metal mounting plate or tab. If you hold it so that the tab is at the back, from the left the pins are Cathode, Anode, Gate. With no trigger, it should have infinite resistance in both directions between the Anode and the Cathode ( i.e. pins 1 and 2 ). If it is shorted, Anode to Cathode, that would explain why the speed control pot has no effect on the speed of the wirefeed motor. This test can be done with the "Diode Test" range of a normal DVM.

    However, the fault that you now see may not be the SCR, it could be some other component on that PCB, causing the SCR to be permanently triggered "on".

    Your machine had been fitted with a replacement wirefeed motor speed control PCB ( Picture 1 ), and that unit worked. The original PCB had a defective auxiliary 12v transformer. After replacing that transformer ( and the relay ), the original PCB works, in that on pressing the MIG torch trigger, the relay which controls power to the main transformer operates correctly now, and the torch is no longer permanently live. However, the wirefeed speed control part of that PCB does not work. Rather than troubleshoot and fix that circuit, you could re-install the replacement PCB ( Picture 1 ), in addition to the original PCB. The original PCB would only be used for the "torch trigger -> relay" function, and that replacement PCB would again provide the motor speed control. You would wire the screw terminals at the PCB connector: red and black to the welding power output at the large rectifier, and red and yellow to the wirefeed motor.
     
  14. thomp1983 New Member

    Messages:
    13
    Location:
    newark on trent, UK
    Hi Eddie, so had another look at it and I think I must be missing something,

    If I understand you correctly to refit the other pcb with the pot in the first set of pictures I need to do the following,

    Take pin 2 of the original pcb to the input + of the other board,

    Take pin 5 of the original pcb to the input - of the other board.

    Take the output + of the other board to the + wire of the wire feed motor

    Take the output - of the other board to the wire that joins to both the wire feed motor - and the black wire on the left in picture 8.

    With things wired up like that the wire feed motor runs faster than before and strangely the extra board has no effect on the speed bit the original pot adjusts the speed but in reverse so what should be less wire feed is more.
     
  15. thomp1983 New Member

    Messages:
    13
    Location:
    newark on trent, UK
    ok then, we can forget trying to refit the other pcb, I manage to feed 240v into it and it went bang so that's that.

    The scr on the original pcb seems to test fine but what I have found is on the bottom of the pcb there are 2 zener diodes, the one with the blue stripe shows open circuit when tested from both sides whereas the other 1 near it provides two different readings so hopefully that's causing my issues, any advice on a suitable replacement for it?

    [​IMG]

    I also looked into the sparking when striking an arc, upon removing what I think is the transformer I found the following,

    [​IMG]
    [​IMG]

    that silver wire which I assume is the end of one of the windings is supposed to be attached just behind the bottom spade terminal, it fell apart as soon as I touched it.

    [​IMG]

    that's the top terminal of the transformer, the winding is supposed to loop through the terminal next to it but again it just broke up

    Is there a way to repair this? for the bottom one I could use a thick piece of wire and a connector to reattach it to the spade terminal but I'm not sure how I'd fix the top one?
     
  16. Seadog

    Seadog Forum Supporter

    Messages:
    6,973
    Location:
    NE London - UK
    They could be diacs from the look of them. They will conduct in both directions after you exceed its breakover voltage.
     
  17. eddie49 Member

    The "replacement" motor speed control PCB looked like it was a stand-alone component, with just 4 screw terminals. Two - red and black - for power in, and 2 - red and yellow - for output. I had intended for the power input to come from the DC output of the main welding transformer, after the rectifier. This would be about 15v to 25v, depending on the power range switch setting. The power output would just go straight to the motor. I think that in your test, you had the wirefeed control part of the original Sealey board in parallel with the replacement board.
    It is a shame the new board went bang. It has an 8-pin chip on it which may be an NE555 timer, so it was probably a true PWM speed controller.

    Troubleshooting the original Sealey board: testing components in-circuit can give confusing readings, but removing and replacing surface-mount components, without the correct tools, is not easy either. Sometimes cutting, cleaning, and rebridging a PCB track may be easier.

    I am not sure if the two diodes in question are Zeners, Diacs, or just ordinary diodes. As Seadog says, Diacs will conduct only after their breakdown voltage has been exceeded. This is typically 30v. They are used to trigger Triacs in mains-powered light dimmers. A digital voltmeter running on a 9v battery will not trigger a Diac.
    If a diode or a Zener is tested in-circuit, whilst bridged by other components, it should still conduct in one direction, showing "600" or "0.6" on the Diode Test range in a DVM, or less if bridged in parallel by some other low resistance component.

    The "other" diode in your picture above is in parallel with an SMD resistor marked 473, which is 47K Ohms, so that diode may show two values. It is probably OK. The "blue stripe" diode shows open circuit both ways - this is not correct, it must conduct in one direction. Any small diode will do to replace it. The blue stripe is the Anode.
     
  18. eddie49 Member

    Regarding the burnt transformer windings: this is not going to be an easy fix. I am not sure if this is the primary or the secondary. The wire is quite thin, and has tapping points, so I guess it is the primary. **Note: Live AC mains voltages present here !!
    The start and end of each winding, or each tapping point ( for the power range switches ) emerges from the wound transformer core, is crimped to a spade tag, and then goes back into the core for the next part of the winding. Since the wire is aluminium, it cannot be fixed by soldering. As you have suggested, two-terminal screw block connectors, cut from a plastic "barrier terminal strip", would be the way to fix this. The problem is to expose enough of the wire coming out of the transformer winding to be able to grip it, clean off the enamel coating, make the connection, and do all this without more of the wire disintegrating. It's possible that this machine cannot be repaired....!
     
    Last edited: Jan 5, 2020
  19. eddie49 Member

    Perhaps I should have mentioned this before: rather than debugging the motor speed controller, it's possible to upgrade and replace the whole circuit.
    This machine, and many like it, runs the wirefeed motor from the main welding power output, via a simple speed controller. Although this does provide a kind of "synergic" effect of increasing the motor speed as welding power is stepped up, it does mean that when the arc is struck the power input to the speed controller will fluctuate, and so the motor speed and wire feed rate will tend to vary during welding.
    [ There are reputable manufacturers, such as Migatronic, who do use the selected welding power range to alter wire speed, but they do this by adding a bias to a separate motor power supply.]
    Several members of the Forum have added separate stabilised 24v power supplies, and then used generic motor speed controllers - e.g.:
    https://www.ebay.co.uk/itm/PWM-DC-6...-Speed-Control-Switch-Controller/331749125193
     
  20. thomp1983 New Member

    Messages:
    13
    Location:
    newark on trent, UK
    finally this is fixed and working correctly,

    [​IMG]

    I removed the transformer, gently sanded back the coating on the windings enough to allow me to connect a screw terminal to them and then a wire from the other side to the spade tag with this completed on all 3 tags the arc now strikes with no sparks from inside the case.

    To fix the wire speed issue on the original pcb I removed the diode I said was showing continuity in both directions and replaced it with a similer sized diode off the other pcb I damaged last week, with this complete the whole wire speed function works correctly from the original board.

    Thanks for all the help with this it's good to know everything is now how it should have been without all the extra wiring and parts dangling about and it'll be nice to be able to move the torch when setting up without striking up an arc unintentionally.

    Chris
     
    a111r likes this.
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