Have bars, but can't connect to network A60
 

I got a problem with my A60 form time to time. It can't log into the the network, the signal bar on the left of the screen flashes (it has 3 full lines), it says "Limited service" -can't send text or call or receive calls. Its not the Sim , battery or the carrier (tested all those in other phone and they work fine). What could be the fault here?

Hardware is defekt !!

I did narrow the defect down to a weak contact (since it only occurs from time to time) in the PFO, heating should do the trick. How does a PFO look like in a A60?