GSM phone suddenly no reception

Hello, until yesterday the integrated phone in my V70 (Bj 10/2001, MY 2002) has always worked (well, sometimes a bit quiet, but otherwise OK). Now it has no reception any more. That means you can turn it on, it recognizes the SIM card, you can operate the menus etc. But with the reception symbol, always zero bars are displayed (normally so 2..4) and there is no net. At the location and on the network (T-Mobile Austria) it is not located, it has tried several times in different places, and everywhere my other phone has received impeccable. For me this looks like if the antenna cable is interrupted. Maybe only one plug has loosened up… Does anyone know the effect? Or knows where the antenna cable runs and is plugged? Then I could try it myself before I drive cumbersomely to the “friendly”… – thanks & warm greetings, Helmut