Dropped phone leading to poor network signal?

I dropped my A70 and the LCD stopped working. No shattering but I had to have the LCD replaced as it would not light up anymore. After repairing the screen with a third party repair shop, I noticed that I now have signal issues I did not have before. I usually have one bar or no signal and my phone will drop calls fairly frequently now. I had the repairshop look inside my phone and they said that the actual antenna was fine but noticed there was a small dent impression in the metal plate covering motherboard. He told me he himself could not tell if there was damage to the motherboard.

I can understand the damage to the motherboard causing an inability to connect completely, but poor connection?

I use my phone for work and so I really want to know if I can fix this and how I would go about this. Could it be the motherboard causing the connectivity issues? Can this be easily replaced/repaired?