HDMI Output issue


Ok so I have been having issues with output over HDMI. Very often the tv recieves no signal from the STB (9 out of 10 times). However it works fine on AV output. I bought a new HDMI cable suspecting the default one supplied by Airtel might be the culprit. But the issue persist with the new cable as well. As of now I have deactivated my HD pack and using the box as a SD one. But I do wanna get HD working again.Now Airtel informs me that warranty on the box is only upto 6 months and mine is no longer covered. An engineer visit would be charged as well.Now am not sure what the engineer will actually do. Will he open the box and have a soldering iron or something and actually make repairs if something is blown out? How technical are these engineers? And will I still be charged if my issue is unresolved?More than the charges whats putting me off is the fact that I will have to deal with the CC and wait around home hoping the engineer will show up as they will then call last second and reschedule wasting my entire day.Any suggestions?