Strange pattern on black screen

My iPhone 5c fallen into the water.

The next day I brought it to a repair shop and they made the anticorrosive treatment.

After that, my iPhone powered on, but it didn't charge, and the home button and the earpiece speaker were not working.

So I ordered and replaced the speaker, battery, Lightning connector and the home button myself.

After that, my iPhone was charging, and it was recognized by my computer, so the Lightning connector was working good.

But after my fix the screen stopped working! I checked the display connector and tried to disconnect and reconnect it, but the problem is not solved.

Another strange thing is that when I connect the Lightning connector the charging sound loops endlessly every 5/6 seconds.

Now I only see a black screen on the display, and sometimes something like this:

What is your advice? Should I try to also replace the display?

Please note that after my fix the display and digitizer were working without any problem, so I really cannot understand what happened.

This is not my first fix on an iPhone device and I didn't note anything strange during the replacement process.

Could you help me please?

Thank you very much!

Bye