Duff Kemppi?

  1. KemppiFrog Member

    Messages:
    3,210
    Location:
    Aquitaine
    Hi all, first time here.
    I have a Kemppi Super Kempomat. 230v aimed at the autobody trade. Probably built in 1988 (stamp on PCB).
    For the last 16yrs it has been excellent on light steel & ss fabrication. Short time ago it suddenly lost power while on a small job i.e. light load.
    The local agent will not help due to it's age. "Bin it" was the comment.
    I have had a good look inside and there is no sign of any burning, loose connections. The PCB looks fine as well. (yes, I know...) The wire feed works OK and it makes contact but sputters as if is on low power with too much wire.
    So, any ideas? or is it time to bite the bullet? If the PCB probably not worth the hassle as €€€€€ even if available. Anything else I might be able to get from Maplins.
    A new unit here is €1,600. :o so, probably a lesser breed from Welders Warehouse.
    Rgs
    Andrew
     
  2. malcolm

    malcolm & Clementine the Cat

    Messages:
    9,106
    Location:
    Bedford UK
    That's a pain - nice machine. If it happened during use it's unlikely to be a bad connection, but well worth cleaning off anything that will undo, especially anything associated with the earth lead. Also worth cycling switches in case there is dirt.

    Does it work with lower wire speed? Might just be something like a diode gone on the rectifier - PCB is more to do with wire speed control.

    There are plenty of independent repair places - could be worth taking it elsewhere.
     
  3. KemppiFrog Member

    Messages:
    3,210
    Location:
    Aquitaine
    Thanks for coming back quickly Malcolm. I will give it a go at low wire speeds.
    The diodes did come to mind, but need to strip it down completely. Several hefty bits on the rectifier plates.
    As for a nice machine, I started MIGing with a cheap 100amp unit. The quality of build in the Kemppi is impressive, which is why I am loth to give up on it.
    A

    Couple of extra comments:
    I tend to use it on max power a lot of the time, as I normally use it on 2/3mm steel, and it is a fairly low amp unit.
    Not sure how much the PCB is involved. But the power is continuously regulated rather than stepped.
     
  4. KemppiFrog Member

    Messages:
    3,210
    Location:
    Aquitaine
    Bit more: From another forum it has been sugested that it might be the diodes. I will test them and report back.
    A
     
  5. KemppiFrog Member

    Messages:
    3,210
    Location:
    Aquitaine
    Well, I looked at the big diodes on the rectifing bit, and all three were open circuit. Now looking to find new ones. Any ideas on where? Odd bit is that they have small wires on the output side, running off to the PCB.
    A
     
  6. mike 109444

    mike 109444 Member

    Messages:
    4,254
    uk Bristol
    Surrly if the diodes were open circuit then you would not get any power at the wire tip. If you are using a multi meter on it's Ohms range then you WILL see no circuit accross the diodes. you need a meter with diode test on it. Or if you are happy (safe) to do so then power on mc and check for DC voltage out of the diodes with ref to the m/c frame is usually good enough for basic check. This won't tell you is the diodes are breaking down under load though.
     
  7. KemppiFrog Member

    Messages:
    3,210
    Location:
    Aquitaine
    Mike, I have a Fluke 70 with diode test. All three were open both ways. But there are six smaller diodes in sets of three linked, that might have given me some power. They test OK. I will do a 'live' test and see if any difference.
    Andrew
     
  8. Fintray

    Fintray Forum Supporter

    Messages:
    780
    Location:
    Aberdeenshire (UK)
    Hopefully they should have some identification on them that will help you locate either direct replacements or a suitable alternative.
     
  9. R Kraft Member

    Messages:
    970
    Wyoming,USA
    If is continuously variable,the diodes you checked,may be SCRs.
    Robert
     
  10. KemppiFrog Member

    Messages:
    3,210
    Location:
    Aquitaine
    R Kraft, sorry, not familiar with the term SCR. These look like stud diodes with tails and have T-151-100 on the side. 151 (amps?) 100 (volts?)
    A
     
  11. Fintray

    Fintray Forum Supporter

    Messages:
    780
    Location:
    Aberdeenshire (UK)
  12. eddie49 Member

    As has been suggested, a MIG with variable ( rather than stepped ) output power may be using thyristors ( or "SCRs" - silicon controlled rectifiers ), rather than simple diodes. This appears to have been confirmed by the part numbers, and the fact that they have a third "thin" wire, in addition to the mounting stud and the heavy braided pigtail. This is the connection to the "gate", which turns the SCR "on" and makes it act like a diode. About 3 volts is needed on that wire to trigger it on; without it there will be no conduction in either direction. That is why your diode tester indicates an open circuit both ways. The welder power is controlled by varying the length of the trigger pulse, in relation to the start and end of each AC half-wave - similar to a light dimmer switch.
    So these components are probably not faulty, the error will be on the PCB which generates the trigger pulses. Further investigation would require the circuit diagram of that board, and an oscilloscope.
     
  13. KemppiFrog Member

    Messages:
    3,210
    Location:
    Aquitaine
    Thanks Eddie, that all makes sense. Problem now is to find someone to check the PCB. As I said in my first post, the local Kempii agent is not interested due to it's age. A local builder is putting me in touch with an electronics guy, fingers crossed here.
    A
     
  14. KemppiFrog Member

    Messages:
    3,210
    Location:
    Aquitaine
    Well, thanks to a link from this forum, Ashley Tinker fixed my PCB and my welder is back in business.
    Thanks to all for your help.
    KF
     
    a111r likes this.
  15. Orn New Member

    Messages:
    4
    Location:
    Iceland
    Hi Andrew. Sorry to revive an old thread but do you happen to know what was wrong in the PCB board? Im having a similar problem with my Kempomat
     
  16. Fintray

    Fintray Forum Supporter

    Messages:
    780
    Location:
    Aberdeenshire (UK)
    Orn likes this.
  17. KemppiFrog Member

    Messages:
    3,210
    Location:
    Aquitaine
    Still about guys:laughing:
    It was a small condenser in the power supply part of the PCB. Easy fix if you know what to look for (which I didn't). I still have the welder, but use only occasionally as a I have a Portamig 285, bought of another member here.
    KF

    By the way, Orn, welcome to the forum.

    If I have a moment later, I will take a photo of the PCB and indicate which bit it was.
     
  18. Dennis Aspö

    Dennis Aspö Member

    Messages:
    1,149
    Location:
    Finland
    I figured it was a condenser (capacitor), probably a yellow RIFA one. I swapped two of those on an old 150A kemppi stick welder from thje 80s and it started welding beatifully. Previously it was really choppy. It was that machine which made me think single phase rectifiers couldn't possibly be any good.
     
  19. Orn New Member

    Messages:
    4
    Location:
    Iceland
    Hey guys, thanks for the warm welcome and quick replies:) I´m glad you still have your old Kempomat, a picture would be greatly appreciated. It would make sense to check and replace the capacitors since they are relatively old and reside in harsh conditions. This is my PCB board, it seems to have Phillips caps instead of RIFA, if I am looking at the right ones...

    Thanks again,
    Orn

    [​IMG]
     
    KemppiFrog likes this.
  20. KemppiFrog Member

    Messages:
    3,210
    Location:
    Aquitaine
    Orn,
    No need for a photo; The part that failed was the component slightly left of the centre of your photo. Gold/yellow ring round the writing with 470163 on the top.
    Ashley charged £50 + postage, sight unseen, to fix it. Very happy with that. The bit is probably 50cents, but he knew how to find and fix it. I didn't.

    Apart from that, I converted the fixed torch to a Euro version with a conversion kit from Welders Warehouse. Very good idea! That was 14 yrs ago. So likely the bits are available much cheaper now.

    Edit: I think Dennis Aspö might have been talking about big caps on the output of a transformer welder, rather than the PCB.
     
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