Hi,
You need to post a picture of the component on the board and a picture and part number of the GPU and maybe someone will be able to help you out.
You are unlikely to get a schematic easily.
The only chance you have is to contact the manufacturer of the GPU, for example PowerColor or Sapphire etc. Open a support case and send them a picture of the component along with the id number on the motherboard. They might be able to look up their parts database for you.
If there is a similar component on the board then use a digital multimeter and measure it's value (resistance or capacitance). The component may be an inductor or a fuse which are more difficult to measure and you will usually need a more complex piece of electronic measurement equipment to determine component value.
There used to be Web sites where schematics were "reverse engineered" for laptop motherboards etc so people could repair their own devices. I get the impression some may have been sued out of business, but I do not know for sure. Perhaps not enough people are prepared to attempt to repair their own equipment, and not enough people were buying the reverse engineered schematics so the business simply could not survive.
Now many devices including GPU's are so difficult to take apart that there is a risk of breaking more things during disassembly than what you attempt to fix. Nvidia reference GTX2080 is definitely an example of this. Thankfully AMD Radeon 7 has not followed that trend.
I do not have a HD7870 here, and I would really need an exact matching card from same manufacturer anyhow.
Sorry I cannot be of more help.
Bye.
