Thermal Arc GM180 wire speed control

[SirDick Diodenob esquire]

Having problems with wire speed , used a stop watch and its doing 1.4m/minute , using 0.8mm wire and will not adjust , I am thinking thats good for nothing as the range on the front plate shows 3m to 15m maximum/minute ?

The pcb board is made by Cigweld dated 10 July 97 type X4811 and have been unable to find a circuit diagram for it . The board is double sided approx 7x10cm and controls the gas valve/contactor coil/fan as well as speed control . In addition to the speed pot there is a 10k ohm pot for burn back . I am thinking the speed control pot has failed but cannot identify it as unlike the burnback pot it has no markings , nearest I can find in the RS catalogue is 263-3135 which looks the same but only goes down to 10k ohm but in addition am not sure of the internal wiring of the pot . I am assuming from the RS catalogue that its a single shaft 11mm ( snap in ? why is it called snap in ? ) . Assuming pin 1 is far left and pin 4 far right is a dummy then the wiper should be pin 2 ? I am getting 2.7k ohm accross 1 and 3 and 2.8k ohm on 1 and 2 no matter what position shaft is in , there could be components in parallel on the other side of the board causing this reading and maybe it could be a 10k ohm pot ? I am planning to short out 1 and 2 to see if it goes to maximum speed , would this be ok or might damage the integrated circuits if I have got it wrong ?

 

[500e]

Having problems with wire speed , used a stop watch and its doing 1.4m/minute , using 0.8mm wire and will not adjust , I am thinking thats good for nothing as the range on the front plate shows 3m to 15m maximum/minute ?

The pcb board is made by Cigweld dated 10 July 97 type X4811 and have been unable to find a circuit diagram for it . The board is double sided approx 7x10cm and controls the gas valve/contactor coil/fan as well as speed control . In addition to the speed pot there is a 10k ohm pot for burn back . I am thinking the speed control pot has failed but cannot identify it as unlike the burnback pot it has no markings , nearest I can find in the RS catalogue is 263-3135 which looks the same but only goes down to 10k ohm but in addition am not sure of the internal wiring of the pot . I am assuming from the RS catalogue that its a single shaft 11mm ( snap in ? why is it called snap in ? ) . Assuming pin 1 is far left and pin 4 far right is a dummy then the wiper should be pin 2 ? I am getting 2.7k ohm across 1 and 3 and 2.8k ohm on 1 and 2 no matter what position shaft is in , there could be components in parallel on the other side of the board causing this reading and maybe it could be a 10k ohm pot ? I am planning to short out 1 and 2 to see if it goes to maximum speed , would this be ok or might damage the integrated circuits if I have got it wrong ?

Snaps into print board then soldered, the 4th leg is likely to be a tap say the pot is 10k the tap could be a fixed tap at 8k or a moving tap 2k away from main slider so the pot could be main 5k tap at 7k or 3k.
Look carefully around blue body edge for faint value.
If nothing unsolder & look at back mite be something there but usually on side,

 

[SirDick Diodenob esquire]

Thanks 500e , I shorted pin 1 to 2 and nothing happened ( put on welding gloves and helmet just in case ) , shorting pin 2 to 3 the motor speeds right up to what could be maximum so I am thinking it is the pot so will try and remove it and have a look underneath for some ID , looks very fiddly to remove but will have a go . With a screwdriver just touching pin no 2 the motor makes a lot of noise , maybe RF signals being picked up by the screwdriver as an arial then somehow being amplified and the output to the motor modulated by it ?