Hi all,I bought a second hand murex 245 a couple of weeks ago as a non runner.When I got it home I found that the earth would not engage.This was due to a relay on pcb being corroded so I took the relay apart cleaned it put it back in,easy fix.Now after a run of weld the wire stick out is 40mm,there,s no burn back adjustment on this welder.I,v checked all connections leads and come up with nothing.Has anyone else had this problem,any help would be great,thanks.
- Thread starter mofitz
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mike 109444
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Sound like what ever should be doing the motor braking is not working. Relay ?
mike 109444
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There maybe a separate relay for the braking. Pics of pcb ...???
mike 109444
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Is it possible that you have accidentally selected the "Spot" or the "Stitch" mode instead of "Continuous" ??
mike 109444
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If it is still in Spot or Stitch even though it's set to Cont then could be . One way to check would be to ramp the t1 and t2 delays right up or down and see if that changes the amount of run on.
Another point Is there still power at the wire while it is running on ? (you may have a small spark from the capacitor(s) as they may have a little charge in them)
Another point Is there still power at the wire while it is running on ? (you may have a small spark from the capacitor(s) as they may have a little charge in them)
There is no power in the wire while it is running on as for the control stuck on stich or spot Ill check it tomorrow.I had one of these welders a few years ago,it too had a problem with pcb which was a simple enough fix(thanks to this site)I regret selling it now.Will let you know how I get on,thanks mike.
mike 109444
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It may use the same relay that supplies power to the motor by shunting it to 0 volts via a resistor to PULL the voltage down when the relay drop back out.
As the motor is running at say 2000 rpm then through gearing the final output is 20 rpm, the residue voltage may be enough for the motor (2000rpm) to run for a second or so thus giving you a couple of turns at the output.
As the motor is running at say 2000 rpm then through gearing the final output is 20 rpm, the residue voltage may be enough for the motor (2000rpm) to run for a second or so thus giving you a couple of turns at the output.
mike 109444
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NotANormalCoder
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The relay only controls the main contactor on this PCB, that switches on the weld current.
Your problem is with the motor 'Braking' side of the circuit.2 Likely problems - The big resistor at the top of your first picture has failed or has poor soldered connections. It should be 0.56 ohms, so measure it with a meter and if it's open circuit or very high resistance, it will not stop the motor at the end of a weld. It is tempting to replace the resistor with a wire link but doing this will casue too much current through the braking transistor and destroy it. Second problem is the braking transistor on the single finned heatsink (again at the top right of your picture). This switches on at the end of the weld, shorting the motor through the resistor previously mentioned, causing it to stop quickly. The transistor is probably an IRF9530 but check the case markings or the printed value on the pcb as there were a couple of different types.
The transistor is easily available but static sensitive so take care when fitting. If it's neither of these faults, then it's more complex. I have service exchange boards for these and can negotiate price/delivery if you need one. PM me for circuit info if you need it.
Dave
Your problem is with the motor 'Braking' side of the circuit.2 Likely problems - The big resistor at the top of your first picture has failed or has poor soldered connections. It should be 0.56 ohms, so measure it with a meter and if it's open circuit or very high resistance, it will not stop the motor at the end of a weld. It is tempting to replace the resistor with a wire link but doing this will casue too much current through the braking transistor and destroy it. Second problem is the braking transistor on the single finned heatsink (again at the top right of your picture). This switches on at the end of the weld, shorting the motor through the resistor previously mentioned, causing it to stop quickly. The transistor is probably an IRF9530 but check the case markings or the printed value on the pcb as there were a couple of different types.
The transistor is easily available but static sensitive so take care when fitting. If it's neither of these faults, then it's more complex. I have service exchange boards for these and can negotiate price/delivery if you need one. PM me for circuit info if you need it.
Dave
