Black moving stripes on the screen. Can it be problem with RAM?

The phone has experienced a series of sudden screen blackouts (black moving stripes on the screen) along with getting significantly hotter. All the blackouts lasted for several seconds and led to a shut down.

Soft reset helped for about 3 shut downs, but after this the phone has stopped responding at all. I got an error when have tried to update it through DFU mode. Also iTunes didn’t show serial number of the phone.

I took it to the local service center. After diagnostic they said that the problem with the RAM and they can’t fix it.

But now I can turn it on and even uploaded firmware. Unfortunately the screen has had blackouts again right over an apple logo and the phone restarts until the battery dies.

Can you please tell me, if this behavior sounds like RAM is damaged indeed? And is it worth trying to fix it or the service guys were right about it?