Numig 155 wire feed

[Hutcho]

Hi guys - have this welder and it works ok but the wire feed seems to fast even if the pot is at zero - higher the voltage the faster it goes - is they a way to slow it down ?

 

[eddie49]

The fault could be due to a collector - emitter short-circuit on the diamond-shaped 2N3055 power transistor.

The metal case of the transistor is the collector, and the emitter is the left-hand pin when looking at the underside with the two pins below the centreline. If you disconnect the external wires and plugs from the board that should be enough to make the measurement for a short, using the Diode Test range on your meter, but you may need to unsolder the transistor to confirm it.

 

[Hutcho]

The fault could be due to a collector - emitter short-circuit on the diamond-shaped 2N3055 power transistor.

The metal case of the transistor is the collector, and the emitter is the left-hand pin when looking at the underside with the two pins below the centreline. If you disconnect the external wires and plugs from the board that should be enough to make the measurement for a short, using the Diode Test range on your meter, but you may need to unsolder the transistor to confirm it.

Thanks Eddie - will give it a go ,

 

[Hutcho]

Morning guys - checked that and it’s ok all good - from zero on wire feed it starts of at 17v and drops down as you select different power settings - I understand that this is how it is but it’s too fast still

 

[Hutcho]

Gone a different route - put a pwn controller instead - that’s slowed it down - what you think ?

 

[Hutcho]

Pwm even

 

[eddie49]

Looking at the components on the PCB, the 8-pin chip suggests that the speed control is already PWM. The chip may be an LM741, or similar, Op-amp, wired to send pulses to the 2N3055 power transistor. If it is running too fast, that could be due to an out-of-spec capacitor.
However, new stand-alone PWM controllers are so cheap, it is probably better to install one than bother with the cost of troubleshooting the original PCB.

 

[Hutcho]

Looking at the components on the PCB, the 8-pin chip suggests that the speed control is already PWM. The chip may be an LM741, or similar, Op-amp, wired to send pulses to the 2N3055 power transistor. If it is running too fast, that could be due to an out-of-spec capacitor.
However, new stand-alone PWM controllers are so cheap, it is probably better to install one than bother with the cost of troubleshooting the original PCB.

Seems to work ok with it - but yeah from another thread you was replying too you said it was a pwm -