Smallfry
HE's Spartacus.
- Messages
- 1,298
- Location
- Kent UK
First post about my old Telwin MIG welder that has decided to play up. I bought it new in 1984 from my Mums friends, who ran a welding supply company. It was a lot of money relatively back then, and I distinctly remember him saying "it will last a lifetime". I am very annoyed to discover that he lied !
It is a Mastermig 120, and I cannot find any posts about them on this whole forum, unless I am doing something wrong ! On this model, there is no wire feed adjustment, it is automatically changed along with the power setting. It does have a max/min changeover switch which alters the feed speed, but only marginally.
Main problem is that the 8 position rotary selector switch, apparently correctly called a "Rotary Cam Switch" has partially failed, which caused intermittent contact in some positions, and complete failure in others. Sometimes I get wire feed but no welding current, and sometimes vice versa.
The whole machine and parts is no longer serviced by Telwin, and even the switch manufacturer has changed ownership and direction, and has no info on the switch.
I have worked out how the switch works, and have ordered something to suit. The original incorporated a main on/off switch, but i am going to use a separate switch for this. This is all just mechanical electrics, if you get what I mean, but now we come to the hard part, for me anyway, as I cannot get on with electronics at all, and seem to have a learning block, so although the circuit board is laughably basic to someone who knows electronics, I am a bit stuck !
What makes it complicated, is the automatic wire feed. There is no variable speed control as is normal. There is a couple of resistors and relays/contactors that the wire feed current is switched through, via the rotary switch. It has a min/max switch to alter the feed speed for overhead welding etc, but this never really worked quite right, no matter what I tried the wire speed was always a bit wrong. So...........
I wondered if it is possible to bypass or change this and fit a "normal" rotary control instead ? All the components on the board are big old fashioned stuff like you would find in the back of an old CRT TV back in the days of Radio Rentals.
I assume the wire feed motor is DC, but I cannot see where it changes from the AC output from the transformer to DC. On the highest speed, the motor runs at 44 volts DC, and at the lowest about 19 volts. I thought the easiest way would be to put a rheostat or potentiometer inline on the motor feed cable. Or is there a better way ?
As an aside, because I need a machine to use, and I wanted to explore gasless MIG welding, I bought a little Draper inverter machine which is a lot smaller despite its higher output that does both, plus scratch start TIGand MMA. It also got a Euro torch and connector. I went for this because although I generally like to spend more on quality tools, financial constraints now dictate otherwise, also, now I am getting on a bit, I dont know if I would get the use out of it !
Anyway, it turned up last Friday afternoon, so I unpacked it all, but the 16 amp plug on, and set it up. Switched it on, and NOTHING. Checked the leads and power feed which was all OK. I then rang the supplier to ask about replacement and if I could take the covers off to chase the fault, not wanting to get into a bunfight over warranty, BUT, they had all gone home. So I took the top off anyway. There is power to both sides of the on/off switch, but that is as far as I can go with it.
Overall impression is that it all looks rather flimsy and fragile compared to the old Telwin. There is a lot of tiny components on the circuit boards, which are all unprotected, and I do not feel it would last anything like as long. So yes, I will be able to get a replacement, but should I ? Should I use the opportunity to just get a refund, and fix the old Telwin, which, once fixed, I am sure will see me out ?
It is a Mastermig 120, and I cannot find any posts about them on this whole forum, unless I am doing something wrong ! On this model, there is no wire feed adjustment, it is automatically changed along with the power setting. It does have a max/min changeover switch which alters the feed speed, but only marginally.
Main problem is that the 8 position rotary selector switch, apparently correctly called a "Rotary Cam Switch" has partially failed, which caused intermittent contact in some positions, and complete failure in others. Sometimes I get wire feed but no welding current, and sometimes vice versa.
The whole machine and parts is no longer serviced by Telwin, and even the switch manufacturer has changed ownership and direction, and has no info on the switch.
I have worked out how the switch works, and have ordered something to suit. The original incorporated a main on/off switch, but i am going to use a separate switch for this. This is all just mechanical electrics, if you get what I mean, but now we come to the hard part, for me anyway, as I cannot get on with electronics at all, and seem to have a learning block, so although the circuit board is laughably basic to someone who knows electronics, I am a bit stuck !
What makes it complicated, is the automatic wire feed. There is no variable speed control as is normal. There is a couple of resistors and relays/contactors that the wire feed current is switched through, via the rotary switch. It has a min/max switch to alter the feed speed for overhead welding etc, but this never really worked quite right, no matter what I tried the wire speed was always a bit wrong. So...........
I wondered if it is possible to bypass or change this and fit a "normal" rotary control instead ? All the components on the board are big old fashioned stuff like you would find in the back of an old CRT TV back in the days of Radio Rentals.
I assume the wire feed motor is DC, but I cannot see where it changes from the AC output from the transformer to DC. On the highest speed, the motor runs at 44 volts DC, and at the lowest about 19 volts. I thought the easiest way would be to put a rheostat or potentiometer inline on the motor feed cable. Or is there a better way ?
As an aside, because I need a machine to use, and I wanted to explore gasless MIG welding, I bought a little Draper inverter machine which is a lot smaller despite its higher output that does both, plus scratch start TIGand MMA. It also got a Euro torch and connector. I went for this because although I generally like to spend more on quality tools, financial constraints now dictate otherwise, also, now I am getting on a bit, I dont know if I would get the use out of it !
Anyway, it turned up last Friday afternoon, so I unpacked it all, but the 16 amp plug on, and set it up. Switched it on, and NOTHING. Checked the leads and power feed which was all OK. I then rang the supplier to ask about replacement and if I could take the covers off to chase the fault, not wanting to get into a bunfight over warranty, BUT, they had all gone home. So I took the top off anyway. There is power to both sides of the on/off switch, but that is as far as I can go with it.
Overall impression is that it all looks rather flimsy and fragile compared to the old Telwin. There is a lot of tiny components on the circuit boards, which are all unprotected, and I do not feel it would last anything like as long. So yes, I will be able to get a replacement, but should I ? Should I use the opportunity to just get a refund, and fix the old Telwin, which, once fixed, I am sure will see me out ?