Chris Wilson
New Member
- Messages
- 5
After 12 years of sterling low current usage my trusty and dry stored Migatronic 220 MTE Dialog has thrown a wobbler. I run it on UK single phase mains, on a 80 amp supply. I very rrarely run it at all hard, i am a race car engineer and most jobs are thin ali work, and thin stainless. The AC over voltage on the torch socket warning light is on all the time, even when idle and just powered up in AC mode. On AC the current is uncontrolled at the torch when the torch button is pressed. If I turn it to DC with the unit powered up it instantly draws MASSIVE current off the single phase mains, and emits an alarming low hertz buzzing. This is without the torch switch being activated. i just have to switch it to the DC setting. I took the covers off (I am a licenced radio ham, so have some electronics knowledge, and understand good high voltage and high current safety techniques), and had a quick poke about. R1, a 10 ohm wire wound over ceramic resistor with a slidable tap, on top of the cooling fan, has heated to failure. The section from M3 pin 3 to M3 pin 10 is the section that's had extreme heat, and the ceramic former is shattered. The other "half" shows no sign of distress. The overheated section has failed open, and is dangling into the fan blades. I am trying to understand the schematic and work out what would have caused one section of R1 to heat so badly. I suspect a thryristor / rectifier in the secondary has failed, but I am unsure. Are these proprietary, or is it a known commercially available Thyristor? The scematic fails to ID the type. Anyone familiar with the workings of these things? All the (Mark I) control panel functions seem alive and well, the current digital display ramps up and down, gas control, blah blah still responds. it seems a control switch or rectification issue, (I think....). Thanks!