Guide/Tips to repair Video card

HI, I got videocards here with different problems.

Can somebody help me or give me guidance repairing videocard?

I really want to learn how to find problems on videocar board/chips/Capacitor.

Mostly problems are:

With power but no Display.

Garbled/Garbage display when drivers are installed.

Thank you in advace guys.

I hope you teach me some techniques troubleshooting problems when it comes to video card problems.