Was slightly working now not at all.

I have just got this camera from Facebook marketplace.

When I met with the seller, upon powering it on, briefly the camera settings (such as ISO and Shutter Speed) could be seen in the viewfinder, however the LCD stayed black. The flash too would work during this time.

Everything that was working:

• Camera Settings in the viewfinder
• Flash would actuate, not actually flash
• Auto-focus

Things that weren't working:

• Camera mirror
• LCD

I followed the guide to replace the LCD but instead of replacing it, I unplugged and replugged the screen. When assembling it all again, I now have nothing showing, in the viewfinder or LCD. The flash is now no longer working.

Everything now not working:

• Flash Actuation
• Camera Settings
• Auto-focus maybe??
• Everything that wasn't working originally

I should also mention I have tested that the lens recieves power with a multimeter. I also checked the LCD and it recieves ~4.5V on what I assume is the main power line for it, other components recieve 3.3V and 1.8V. I have checked the battery too and am getting 7.4V+.

I am not too sure where to look now and would like some pointers on where to look next. In the meantime, I will probably end up tracing all the circuits or checking the viewfinder display to find why that stopped working.

Updated: Things Checked/Done:

• Unplugged and replugged all cables on the front panel.
• Checked every capacitor/volatile component.
• Unplugged and replugged all cables to the motherboard, during this found that the on/off switch ribbon was almost out.
• Manually actuated the flash and mirror gearboxes, they reset (and scared me) when reassembled and powered on.
• Tried two different batteries, both fully charged.
• Tried with and without SD card.

Thank you for your time.