Black screen, ribbon cables intact, battery OK, restored

my iPhone (used only as iPod, no cell service) has a black screen nearly all the time. Occasionally, on pressing Home or Power buttons, active screen appears. Shows as working when connected to my MacBook via iTunes. I recall 2 or 3 occasions before this when screen was black when I thought the phone was on; this may be the relatively sudden advance of an earlier-begun "disease." I have so far reset it (no help) and restored it--twice. Still (almost always) black screen. Between restores, I popped the back, removed battery, and unhooked and rehooked all the easily accessible cable connectors (they all seemed snug when I pulled them). So I had the battery out for that time. Most I've seen of the screen was when it came on during/after the first restore, and looked normal while it lasted. Doesn't flicker or distort, just goes black. Battery, last checked, seemed to hold decent charge, so I'm suspecting deeper trouble. No major drops that I'm aware of. Saw a YouTube vid about a black screen repair job where someone replaced battery, then some other part, neither helped, then the "digitizer." What's that and could that be the trouble? And worth the repair. I'm comfortable going in again to replace parts. Thank you!