How to troubleshoot phone problem

[Android Central Question]

Hi guys

I have 2 Galaxy S7 edge smartphones.

Neither of which work.

1 has a cracked screen and when I power it up the screen flickers green, most of the time I can't see a thing and at times I can see the top 3rd of the screen just about.
When I plug it into my linux laptop it appears in the list of usb devices.

The second is just lifeless. Screen is fine. Glass perfect, no scratches, not dropped. Nothing.
When I plug it into the computer I get nothing.

When I place them on my wireless charging pad both make the pad go blue, like they are charging. Fine.

I disassembled both phones.
I took out the battery, and motherboard.
I swapped these parts around.

Both phones respond as before. Exaclty the same.

The cracked one still turns on green, the other is still dead.

I was hoping to make one working phone.

If the LCD that appears fine is damaged shouldn't the phone go on?
Shouldn't it appear in my usb device list?

Any help troubleshooting the problem is appreciated.

Thanks

 

[VW Maverick]

Welcome.
Will move this to the S7 forum for more visability.

Mav.

 

[Rukbat]

You have one (badly) cracked screen, so that phone won't show anything but what it shows.

The other one could have a dead screen, so no matter which motherboard and battery you put in it, it won't work.

Measure the battery voltages to make sure they're charged. If not, leave them charging overnight.

 

[MadridBill]

You have one (badly) cracked screen, so that phone won't show anything but what it shows.

The other one could have a dead screen, so no matter which motherboard and battery you put in it, it won't work.

Measure the battery voltages to make sure they're charged. If not, leave them charging overnight.

That was the round about detailed way of asking my question...

If it has a dead screen, shouldn't it go on? The lights at the top show? Or at least show up when plugged into my PC and I press to power it up?

And if it isn't a dead screen then I would have thought merging the 2 would make one work....

 

[MadridBill]

Oh, and the batteries are charged, that shows on green screen phone.