We have a thyristorised welding machine in our company.The current was not changing on rotating the potentiometer.

I checked the potentiometer, the resistance across its extreme terminal and middle terminal was changing on rotating the potentiometer.

Can anyone suggest something?

 

> Can anyone suggest something?

Sounds like you will have to go further than the pot. Hanging a scope on the gates will give a better idea of what is going on.
Maybe shorted Thyristors? Bad control board?
Best get someone on the scene who is familiar with such circuits.

Cheers
Gerald Beaudoin

 

My suggestion would be to use an oscilloscope to see any type of waveform to help troubleshoot the problem you are having. By probing the wiper you will be able to see the voltage increase and decrease.

trueblue
http://www.magneticencoders.org