Murex Transtig 160 Dc Faulty.

I have a Murex Transtig 160 DC welder that has only 3 to 4 hours use from new , that wont work correctly. Firstly it will work perfectly in the Arc welding setting,but when I set it up for DC TIG welding , all I get is the HF tiny spark, no error codes show on the display . although the internal back up battery must now be over 6 years old,( the manual states a 5 year life expectancy).All the features on the display work fine,

Everything on the welder is still as new IE. the leads +tip holder+earth lead .Maybe Not important but I bought another Murex welder in frustation back then, when i failed to get the above one working. The 2 ND. one is AC- DC 200 amp. and it works faultlessly.The bussiness I bought the 160 DC. from changed ownership, and were not interested. I would like to hear from anyone with experience with This actual problem , in fact any help appreciated.