Hi We have a vey old Miller Matic 35. We are having wire feed problems. The speed is not adjustable, the knob is not working. One speed fits all...well not really. It is inconsistent. It starts off at a normal speed, stops, then goes really slow. Do you have any suggestions on where to start? Thanks, Lindsay

The problem with your unit is as a result of two things. The first being the power source, if the power source is not meant to support heavy equipment such as your unit then the speed which it goes at will definitely fluctuate and after a time it would drop to a slow pace.
Also the control knob which is not working could be the cause, due to the vibration of the system the inner workings of the knob could adjust itself to the lowest point as the external part doesnt work you dont see any movement on the knob.
Finally the transformer inside the unit might be bad and the symptoms which are being displayed are just pre-pack-up signs which are being displayed. Check out these three options and get back to me.
Hope this solution has been helpful?