I bought this welder as 'for repair or spares' a few years ago and have spent a lot of time trying to put it into order. I will first say how it behaves now: set to TIG DC the HF is just about absent, just a momentary spark (but by 'scratching' the arc can be started and welding works perfectly); on TIG AC it works well enough for welding. Set to MMA everything looks right for about 7 seconds after switch-on, then the screen shows 3 dashes and the yellow (overheat warning) light flashes at about 1 per second. Does anyone know what the light doing this signifies?
Now an account of repairs and observations to date: On first switching on, a fan came on but nothing showed on the screen. I found that there was no 'logic' power on the main board, but the big capacitors were at about 340v. Applied external DC to the voltage regulators in the supply to the 'logic' area of the main board, and control lights etc lit up. Eventually put right the DC supply to all that (fault was blown PWM components in its small DC - DC converter). Tried welder. It worked, but output power rather feeble, about 40a max. Watched innards when welding, and saw a snubber resistor in main inverter glowing red. Shut down, long period of tracing through circuitry, checking many things. Eventually 'scope on PWM IC controlling inverter showed it running at about 800 kHz. Alarm bell. Snubber glowing explained. Found timing capacitor for PWM IC (UC3524) failed (surface mount component came off board in 2 pieces when un-soldering). Fitted suitable replacement, now runs at about 100kHz. Welder worked perfectly for several months, and quickly became my favourite welder for all TIG jobs. Then failed again. Opened it, saw a snubber resistor glowing again. Soon found that associated diode was short circuit. (Snubber is capacitor in series with parallelled diode + resistor. Still don't understand how shorted diode allowed MORE current to flow through resistor!) Replaced it (with correct part). Now welder behaves as described above.
HF board thoroughly examined and tested. It works perfectly, when fed with suitable signals. Can't properly test small board with controls attached, because it has a 44 pin microcontroller. My theory has been that the welder thinks that the arc has started and so shuts off the HF prematurely. But the rectifier output (about 75v OCV) tapping into the 'logic' board seems intact, and the output of a current transformer before the inverter rectifier seems to send an appropriately low signal into the logic board when no welding current is flowing. (On AC welding the HF gives a spark at each polarity change, explaining why AC welding is possible.)
I have traced circuitry from a thermistor in the inverter rectifier all the way through the logic board to where its output is sensed and would switch a voltage. It does not switch that voltage, but if I simulate an overheat (putting a low resistance in parallel with the thermistor connections) that voltage is switched. So the yellow light flashing is not indicating overheat. I suppose it means something else, but what?
I should add that Fimer in Italy was very helpful at first, giving me some component values and device designations and diagnostic suggestions, but after a time they understandably indicated that they could help no longer over such an old machine (about 12 years I think).
Now an account of repairs and observations to date: On first switching on, a fan came on but nothing showed on the screen. I found that there was no 'logic' power on the main board, but the big capacitors were at about 340v. Applied external DC to the voltage regulators in the supply to the 'logic' area of the main board, and control lights etc lit up. Eventually put right the DC supply to all that (fault was blown PWM components in its small DC - DC converter). Tried welder. It worked, but output power rather feeble, about 40a max. Watched innards when welding, and saw a snubber resistor in main inverter glowing red. Shut down, long period of tracing through circuitry, checking many things. Eventually 'scope on PWM IC controlling inverter showed it running at about 800 kHz. Alarm bell. Snubber glowing explained. Found timing capacitor for PWM IC (UC3524) failed (surface mount component came off board in 2 pieces when un-soldering). Fitted suitable replacement, now runs at about 100kHz. Welder worked perfectly for several months, and quickly became my favourite welder for all TIG jobs. Then failed again. Opened it, saw a snubber resistor glowing again. Soon found that associated diode was short circuit. (Snubber is capacitor in series with parallelled diode + resistor. Still don't understand how shorted diode allowed MORE current to flow through resistor!) Replaced it (with correct part). Now welder behaves as described above.
HF board thoroughly examined and tested. It works perfectly, when fed with suitable signals. Can't properly test small board with controls attached, because it has a 44 pin microcontroller. My theory has been that the welder thinks that the arc has started and so shuts off the HF prematurely. But the rectifier output (about 75v OCV) tapping into the 'logic' board seems intact, and the output of a current transformer before the inverter rectifier seems to send an appropriately low signal into the logic board when no welding current is flowing. (On AC welding the HF gives a spark at each polarity change, explaining why AC welding is possible.)
I have traced circuitry from a thermistor in the inverter rectifier all the way through the logic board to where its output is sensed and would switch a voltage. It does not switch that voltage, but if I simulate an overheat (putting a low resistance in parallel with the thermistor connections) that voltage is switched. So the yellow light flashing is not indicating overheat. I suppose it means something else, but what?
I should add that Fimer in Italy was very helpful at first, giving me some component values and device designations and diagnostic suggestions, but after a time they understandably indicated that they could help no longer over such an old machine (about 12 years I think).