Transmig 140 PCB component values

  1. stevethegrease New Member

    Messages:
    8
    Location:
    GB
    Does anyone know the part number of the metal cased transistors* on the circuir board? Mine are so rusty that I can't read the numbers. I know its BF something

    I bought my transmig 140 last year and it's often played up, but I had it working reasonably well.
    I decided to re-do the little timer chips so the pulse welding would work . My mate said to solder sockets in as then changing the chips is easy. He was right. I also tidied up a few dry looking joints on the board.
    Upon re-fitting the welder now does the fault described in another post,(54278) after about 2 seconds the contacter pulls in of it's own volition. Its suggested in the post that some of the transistors may have failed , fine ...... but I can't read the part numbers off mine to replace them. When I pull the trigger the feedmotor operates, so is the contactor and the feed motor operated seperately? Does anyone know the pinouts for the board? Or a circuit diagram of the board?
    Advice would be appreciated.
    * or the little black ones
     
  2. eddie49 Member

    The components on the PCB in my Transmig 140 are also dirty/dusty/corroded, so I can only read a few of the numbers:

    The PCB itself is numbered Y 1407934 Issue 1 on the top, 1407933 on the bottom.
    TR101 is a TO-220 power transistor on a heatsink, so is TR107. Both are TIP41A
    TR102 is a metal can, BFX9804 ( ? )
    TR103 is plastic, BC184L
    TR104, TR105 plastic, unreadable
    TR106 metal can, unreadable
    Timer chips TM101, TM102: both 555

    As you know, these early BOC/Murex welders were well-designed and used high quality components, but are let down by very poor soldering on the PCBs, especially the pins for the cable connectors. It's often best to just re-flow every joint.
    The wirefeed motor is controlled by a Variac, so is probably a separate circuit to the Contactor. The Contactor pulling-in by itself implies that the Stitch welding timer has inadvertently been triggered. Does the small relay on the PCB close after 2 seconds, followed by the Contactor? What does the gas valve do?

    EDIT: By magnifying the picture in the other thread you mentioned - https://www.mig-welding.co.uk/forum/threads/murex-transmig-140-wire-always-live.54278/ , I think the metal-can transistors TR102 and TR106 are both BFX85.
     
  3. a111r Member

    Messages:
    903
    Location:
    London
    Hi Steve, I bet it was Chizzel who advised you on the socket!
     
  4. stevethegrease New Member

    Messages:
    8
    Location:
    GB
    Thanks for your advice about the transistor numbers guys, most helpful.
    No, it wasn't Chizzel, but it was very good advice.
     
    a111r likes this.
  5. stevethegrease New Member

    Messages:
    8
    Location:
    GB
    I'm obviously hamfisted with a soldering iron as I chickened out of changing the metal cased transistors on my board, my mate did the job and also removed the plastic cased transisitors to check them . He reckons they are a general purpose NPN type and suggests that they could be similar to a BC546 ,( he was unaware of the comments above ) but the BC 184L mentioned above looks similar to the BC546, the 546 is rated at 65v not 40v so maybe either would do. Hey I'm only trying to help, not my area of knowledge at all. I've not ben able to testmy 'fixed' board yet ( lockdown etc) so I will report back soon.
     
  6. eddie49 Member

    Thank you for the update.
     
  7. stevethegrease New Member

    Messages:
    8
    Location:
    GB
    My Transmig 140 welder is eventually fixed, but apparently one problem that can cause 'the turn on contacter pulls in' problem can be an open circuit or high resistance in the burn back potentiometer circuit. This should be checked from the board as the pins/ connector can give a high resistance. This was the root of the fault on my welder. I can recommend the Ebay circuit board repair service, competent, friendly and helpful.
     
    eddie49 likes this.
  8. eddie49 Member

    That is an interesting and useful bit of knowledge. During burn back the welder keeps going on its own ( minus wire feed ), so that does make sense.
    Was that TecArc, ebay name "yorweldsupplies" ?
     
  9. stevethegrease New Member

    Messages:
    8
    Location:
    GB
    It was indeed 'yorweldsupplies'. The person I dealt with was competent and patient, the customer is not always right and might need gentle suggestions of where additional faults might lie...

    A further update. Since having the crcuit board repaired I decided to do some more investigation, as the welds still seemed poor, and the machine low powered. I removed the leads to the large electrolytic capacitors and removed and cleaned the connections. The old spade connectors go loose so I squeezed them tight with some pliers, some broke , so I replaced those . I took lots of photos so It all went back together correctly ( there are rather a lot of wires , all the same colour)
    There is also a large strip of spade connections, some mains feeds and some to the transformer connections. Many of the male spade connectors were loose on the fixing rivet, or corroded, and again the spade connectors were likewise corroded and nearly all loose. I got two connectors blocks from Ebay - "Weco Terminal Block 4 Barriered Poles Each With 6 Faston Tabs 25A 400V OM0443" and glued them together giving me sufficient male spades to redo all the connections. Each spade connector was again either squeezed tighter or replaced if it was loose or broken. With a couple of photos it was relatively easy to replace all the connections in the correct order. Not all the connections need to be replicated, there are 2 links for the 240/220v connection which duplicate connections and can be discarded. ( the furthest right connections) and the connection made to the appropriate male spade directly.
    What a transformation... the machine is now hugely improved doing lovely runs of weld, as it was supposed to, all for a couple of hours labour, a few spade connectors and these 2 cheap connectors.
    Sorry to go on , but I struggled and this might help someone.
     
    Last edited: Jul 23, 2020
    a111r likes this.
  10. Jpudds New Member

    Messages:
    13
    Location:
    Nuneaton England
    How do I start a new thread, my problem is Transmig not working.
    Relay works, when trigger is pulled contactor pulls in and trips straight out.
    Wire feed and gas start momentarily.while contactor is in.
    Any help would be greatly appreciated
     
  11. a111r Member

    Messages:
    903
    Location:
    London
  12. Jpudds New Member

    Messages:
    13
    Location:
    Nuneaton England
    Thanks for your help.sorry about the delay in responding.
     
Advertisements