DTU 300 no current control at pedal

admin

Hi, new to forum. I have an old DTU 300. Problem is- no current control at pedal. It is off or max current at any position other than off. I can control current at panel current control dial with the panel - remote switch in the remote position. The foot pedal check out with ohm meter. It shows varying resistance with travel from off to wfo. Thanks, Mike Krizan
Reply:Hi My name is Orlando and I am helping mike with his Welder. As he said we have checked the pedal pot and it mechanically works and it varies from about 2 ohms to about 1100 Ohms. We followed the wiring of it and penciled it in to the schematic. The fact that the control panel pot works tells me the SCR's and PCB are more or less working correctly. We checked the switch for panel/remote and it seemed flaky at first but then seemed to work OK but to verify we removed the common and the remote wires and connedted them together but still the pedal was on or off. Weather has been too cold to play anymore but next time we will check voltages to PCB as well as the return voltage to the PCB coming from the panel pot thru the pedal pot and back to the PCB. What I would like to understand it how the SCR's / reactor coil circuit actually work. It would appear the schematic shows part of the reactor under the SCR's but then on the left side of the schematic is what looks like the rest of the circuit.


Reply:PCB schematic